docs/SkCanvas_Reference.bmh

#Topic Canvas
#Alias Canvas_Reference

Canvas provides an interface for drawing, and how the drawing is clipped and transformed.
Canvas contains a stack of Matrix and Clip values.

Canvas and Paint together provide the state to draw into Surface or Device.
Each Canvas draw call transforms the geometry of the object by the concatenation of all
Matrix values in the stack. The transformed geometry is clipped by the intersection
of all of Clip values in the stack. The Canvas draw calls use Paint to supply drawing
state such as Color, Typeface, text size, stroke width, Shader and so on.

To draw to a pixel-based destination, create Raster_Surface or GPU_Surface. 
Request Canvas from Surface to obtain the interface to draw. 
Canvas generated by Raster_Surface draws to memory visible to the CPU. 
Canvas generated by GPU_Surface uses Vulkan or OpenGL to draw to the GPU.

To draw to a document, obtain Canvas from SVG_Canvas, Document_PDF, or Picture_Recorder.
Document-based Canvas and other Canvas subclasses reference Device describing the
destination.

Canvas can be constructed to draw to Bitmap without first creating Raster_Surface.
This approach may be deprecated in the future.  

#Class SkCanvas

#Topic Overview

#Subtopic Subtopics
#Table
#Legend
# topics                 # description                                 ##
#Legend ##
#ToDo generate a TOC here ##
#Table ##
#Subtopic ##

#Subtopic Constants
#Table
#Legend
# constants                      # description                                 ##
#Legend ##
# Lattice::Flags                 # Controls Lattice transparency. ##
# PointMode                      # Sets drawPoints options. ##
# SaveLayerFlags                 # Sets SaveLayerRec options. ##
# SrcRectConstraint              # Sets drawImageRect options. ##
#Table ##
#Subtopic ##

#Subtopic Structs
#Table
#Legend
# struct                         # description                                 ##
#Legend ##
# Lattice                        # Divides Bitmap, Image into a rectangular grid. ##
# SaveLayerRec                   # Contains state to create the layer offscreen. ##
#Table ##
#Subtopic ##

#Subtopic Constructors

Create the desired type of Surface to obtain its Canvas when possible. Constructors are useful
when no Surface is required, and some helpers implicitly create Raster_Surface.

#Table
#Legend
#                                                               # description                                     ##
#Legend ##
# SkCanvas()                                                    # No Surface, no dimensions.                      ##
# SkCanvas(int width, int height, const SkSurfaceProps* = NULL) # No Surface, set dimensions, Surface_Properties. ##
# SkCanvas(SkBaseDevice* device)                                # Existing Device. (SkBaseDevice is private.)     ##
# SkCanvas(const SkBitmap& bitmap)                              # Uses existing Bitmap.                           ##
# SkCanvas(const SkBitmap& bitmap, const SkSurfaceProps& props) # Uses existing Bitmap and Surface_Properties.    ##
# MakeRasterDirect                                              # Creates from SkImageInfo and Pixel_Storage.     ##
# MakeRasterDirectN32                                           # Creates from image data and Pixel_Storage.      ##
#ToDo incomplete ##
#Table ##
#Subtopic ##

#Subtopic Member_Functions
#Table
#Legend
# function                         # description                                                   ##
#Legend ##
# accessTopLayerPixels             # Returns writable pixel access if available. ##
# accessTopRasterHandle            # Returns context that tracks Clip and Matrix. ##
# clear()                          # Fills Clip with Color. ##
# clipPath                         # Combines Clip with Path. ##
# clipRRect                        # Combines Clip with Round_Rect. ##
# clipRect                         # Combines Clip with Rect. ##
# clipRegion                       # Combines Clip with Region. ##
# concat()                         # Multiplies Matrix by Matrix. ##
# discard()                        # Makes Canvas contents undefined. ##
# drawAnnotation                   # Associates a Rect with a key-value pair.##
# drawArc                          # Draws Arc using Clip, Matrix, and Paint.##
# drawAtlas                        # Draws sprites using Clip, Matrix, and Paint.##
# drawBitmap                       # Draws Bitmap at (x, y) position. ##
# drawBitmapLattice                # Draws differentially stretched Bitmap. ##
# drawBitmapNine                   # Draws Nine_Patch Bitmap. ##
# drawBitmapRect                   # Draws Bitmap, source Rect to destination Rect. ##
# drawCircle                       # Draws Circle using Clip, Matrix, and Paint. ##
# drawColor                        # Fills Clip with Color and Blend_Mode. ##
# drawDRRect                       # Draws double Round_Rect stroked or filled. ##
# drawDrawable                     # Draws Drawable, encapsulated drawing commands. ##
# drawIRect                        # Draws IRect using Clip, Matrix, and Paint. ##
# drawImage                        # Draws Image at (x, y) position. ##
# drawImageLattice                 # Draws differentially stretched Image. ##
# drawImageNine                    # Draws Nine_Patch Image. ##
# drawImageRect                    # Draws Image, source Rect to destination Rect. ##
# drawLine                         # Draws line segment between two points.##
# drawOval                         # Draws Oval using Clip, Matrix, and Paint. ##
# drawPaint                        # Fills Clip with Paint. ##
# drawPatch                        # Draws cubic Coons patch. ##
# drawPath                         # Draws Path using Clip, Matrix, and Paint. ##
# drawPicture                      # Draws Picture using Clip and Matrix. ##
# drawPoint                        # Draws point at (x, y) position. ##
# drawPoints                       # Draws array as points, lines, polygon. ##
# drawPosText                      # Draws text at array of (x, y) positions. ##
# drawPosTextH                     # Draws text at x positions with common baseline. ##
# drawRRect                        # Draws Round_Rect using Clip, Matrix, and Paint. ##
# drawRect                         # Draws Rect using Clip, Matrix, and Paint. ##
# drawRegion                       # Draws Region using Clip, Matrix, and Paint. ##
# drawRoundRect                    # Draws Round_Rect using Clip, Matrix, and Paint. ##
# drawText                         # Draws text at (x, y), using font advance. ##
# drawTextBlob                     # Draws text with arrays of positions and Paint. ##
# drawTextOnPath                   # Draws text following Path contour. ##
# drawTextOnPathHV                 # Draws text following Path with offsets. ##
# drawTextRSXform                  # Draws text with array of RSXform. ##
# drawString                       # Draws null terminated string at (x, y) using font advance. ##
# drawVertices                     # Draws Vertices, a triangle mesh. ##
# flush()                          # Triggers execution of all pending draw operations. ##
# getBaseLayerSize                 # Gets size of base layer in global coordinates. ##
# getDeviceClipBounds              # Returns IRect bounds of Clip. ##
# getDrawFilter                    # Legacy; to be deprecated. ##
# getGrContext                     # Returns GPU_Context of the GPU_Surface. ##
# getLocalClipBounds               # Returns Clip bounds in source coordinates. ##
# getMetaData                      # Associates additional data with the canvas. ##
# getProps                         # Copies Surface_Properties if available. ##
# getSaveCount                     # Returns depth of stack containing Clip and Matrix. ##
# getTotalMatrix                   # Returns Matrix. ##
# imageInfo                        # Returns Image_Info for Canvas. ##
# isClipEmpty                      # Returns if Clip is empty. ##
# isClipRect                       # Returns if Clip is Rect and not empty. ##
# MakeRasterDirect                 # Creates Canvas from SkImageInfo and pixel data. ##
# MakeRasterDirectN32              # Creates Canvas from image specifications and pixel data. ##
# makeSurface                      # Creates Surface matching SkImageInfo and SkSurfaceProps. ##
# peekPixels                       # Returns if Canvas has direct access to its pixels. ##
# quickReject                      # Returns if Rect is outside Clip. ##
# readPixels                       # Copies and converts rectangle of pixels from Canvas. ##
# resetMatrix                      # Resets Matrix to identity. ##
# restore()                        # Restores changes to Clip and Matrix, pops save stack. ##
# restoreToCount                   # Restores changes to Clip and Matrix to given depth. ##
# rotate()                         # Rotates Matrix. ##
# save()                           # Saves Clip and Matrix on stack. ##
# saveLayer                        # Saves Clip and Matrix on stack; creates offscreen. ##
# saveLayerAlpha                   # Saves Clip and Matrix on stack; creates offscreen; sets opacity. ##
# saveLayerPreserveLCDTextRequests # Saves Clip and Matrix on stack; creates offscreen for LCD text. ##
# scale()                          # Scales Matrix. ##
# setAllowSimplifyClip             # Experimental. ##
# setDrawFilter                    # Legacy; to be deprecated. ##
# setMatrix                        # Sets Matrix. ##
# skew()                           # Skews Matrix. #
# translate()                      # Translates Matrix. ##
# writePixels                      # Copies and converts rectangle of pixels to Canvas. ##
#Table ##
#Subtopic ##

#Topic Overview ##

# ------------------------------------------------------------------------------

#Method static std::unique_ptr<SkCanvas> MakeRasterDirect(const SkImageInfo& info,
        void* pixels, size_t rowBytes)

Allocates raster Canvas that will draw directly into pixels.
To access pixels after drawing, call flush() or peekPixels.

Canvas is returned if all parameters are valid.
Valid parameters include:
info dimensions are zero or positive;
info contains Image_Color_Type and Image_Alpha_Type supported by Raster_Surface;
pixels is not nullptr;
rowBytes is zero or large enough to contain info width pixels of Image_Color_Type.

pixel buffer size should be info height times rowBytes times bytes required for
Image_Color_Type.

#Param info  width, height, Image_Color_Type, Image_Alpha_Type, Color_Space, of Raster_Surface;
             width, or height, or both, may be zero
##
#Param pixels  pointer to destination pixels buffer; buffer size should be height
               times rowBytes times four
##
#Param rowBytes  interval from one Surface row to the next; equal to or greater than
                 info width times bytes required for Image_Color_Type
##

#Return  Canvas if all parameters are valid; otherwise, nullptr ##

#Example
    #Description
        Allocates a three by three bitmap, clears it to white, and draws a black pixel
        in the center.
    ##
void draw(SkCanvas* ) {
    SkImageInfo info = SkImageInfo::MakeN32Premul(3, 3);  // device aligned, 32 bpp, premultipled
    const size_t minRowBytes = info.minRowBytes();  // bytes used by one bitmap row
    const size_t size = info.getSafeSize(minRowBytes);  // bytes used by all rows
    SkAutoTMalloc<SkPMColor> storage(size);  // allocate storage for pixels
    SkPMColor* pixels = storage.get();  // get pointer to allocated storage
    // create a SkCanvas backed by a raster device, and delete it when the
    // function goes out of scope.
    std::unique_ptr<SkCanvas> canvas = SkCanvas::MakeRasterDirect(info, pixels, minRowBytes);
    canvas->clear(SK_ColorWHITE);  // white is unpremultiplied, in ARGB order
    canvas->flush();  // ensure that pixels are cleared
    SkPMColor pmWhite = pixels[0];  // the premultiplied format may vary
    SkPaint paint;  // by default, draws black
    canvas->drawPoint(1, 1, paint);  // draw in the center
    canvas->flush();  // ensure that point was drawn
    for (int y = 0; y < info.height(); ++y) {
        for (int x = 0; x < info.width(); ++x) {
            SkDebugf("%c", *pixels++ == pmWhite ? '-' : 'x');
        }
        SkDebugf("\n");
    }
}
    #StdOut
        ---
        -x-
        ---
    ##
##

#ToDo incomplete ##

#SeeAlso MakeRasterDirectN32 SkSurface::MakeRasterDirect
##

# ------------------------------------------------------------------------------

#Method static std::unique_ptr<SkCanvas> MakeRasterDirectN32(int width, int height, SkPMColor* pixels,
                                                         size_t rowBytes) 

Allocates raster Canvas specified by inline image specification. Subsequent Canvas
calls draw into pixels.
Image_Color_Type is set to kN32_SkColorType.
Image_Alpha_Type is set to kPremul_SkAlphaType.
To access pixels after drawing, call flush() or peekPixels.

Canvas is returned if all parameters are valid.
Valid parameters include:
info dimensions are zero or positive;
info contains Image_Color_Type and Image_Alpha_Type supported by Raster_Surface;
pixels is not nullptr;
rowBytes is zero or large enough to contain width pixels of Image_Color_Type.

pixel buffer size should be info height times rowBytes times bytes required for
Image_Color_Type.

#Param width  pixel column count on Raster_Surface created; must be zero or greater ##
#Param height  pixel row count on Raster_Surface created.; must be zero or greater ##
#Param pixels  pointer to destination pixels buffer; buffer size should be height
               times rowBytes times four
##
#Param rowBytes  interval from one Surface row to the next; equal to or greater than
                 width times four
##

#Return  Canvas if all parameters are valid; otherwise, nullptr ##

#Example
    #Description
        Allocates a three by three bitmap, clears it to white, and draws a black pixel
        in the center.
    ##
void draw(SkCanvas* ) {
    const int width = 3;
    const int height = 3;
    SkPMColor pixels[height][width];  // allocate a 3x3 premultiplied bitmap on the stack
    // create a SkCanvas backed by a raster device, and delete it when the
    // function goes out of scope.
    std::unique_ptr<SkCanvas> canvas = SkCanvas::MakeRasterDirectN32(
            width,
            height,
            pixels[0],  // top left of the bitmap
            sizeof(pixels[0]));  // byte width of the each row
    // write a pre-multiplied value for white into all pixels in the bitmap
    canvas->clear(SK_ColorWHITE);
    SkPMColor pmWhite = pixels[0][0];  // the premultiplied format may vary
    SkPaint paint;  // by default, draws black
    canvas->drawPoint(1, 1, paint);  // draw in the center
    canvas->flush();  // ensure that pixels is ready to be read
    for (int y = 0; y < height; ++y) {
        for (int x = 0; x < width; ++x) {
            SkDebugf("%c", pixels[y][x] == pmWhite ? '-' : 'x');
        }
        SkDebugf("\n");
    }
}
    #StdOut
        ---
        -x-
        ---
    ##
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method SkCanvas()

Creates an empty canvas with no backing device/pixels, and zero
dimensions.

#Return  empty canvas ##

#Example

#Description
Passes a placeholder to a function that requires one.
##

#Function
// Returns true if either the canvas rotates the text by 90 degrees, or the paint does.
static void check_for_up_and_down_text(const SkCanvas* canvas, const SkPaint& paint) {
    bool paintHasVertical = paint.isVerticalText();
    const SkMatrix& matrix = canvas->getTotalMatrix();
    bool matrixIsVertical = matrix.preservesRightAngles() && !matrix.isScaleTranslate();
    SkDebugf("paint draws text %s\n", paintHasVertical != matrixIsVertical ?
            "top to bottom" : "left to right");
}

static void check_for_up_and_down_text(const SkPaint& paint) {
    SkCanvas canvas;  // placeholder only, does not have an associated device
    check_for_up_and_down_text(&canvas, paint);
}

##
void draw(SkCanvas* canvas) {
    SkPaint paint;
    check_for_up_and_down_text(paint);  // paint draws text left to right
    paint.setVerticalText(true);
    check_for_up_and_down_text(paint);  // paint draws text top to bottom
    paint.setVerticalText(false);
    canvas->rotate(90);
    check_for_up_and_down_text(canvas, paint);  // paint draws text top to bottom
}

    #StdOut
        paint draws text left to right
        paint draws text top to bottom
        paint draws text top to bottom
    ##
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method SkCanvas(int width, int height, const SkSurfaceProps* props = NULL)

Creates Canvas of the specified dimensions without a Surface.
Used by subclasses with custom implementations for draw methods.

If props equals nullptr, Surface_Properties are created with Surface_Properties_Legacy_Font_Host settings,
which choose the pixel striping direction and order. Since a platform may dynamically
change its direction when the device is rotated, and since a platform may have
multiple monitors with different characteristics, it's best not to rely on this
legacy behavior.

#Param width  zero or greater ##
#Param height zero or greater ##
#Param props  LCD striping orientation and setting for device independent fonts;
              may be nullptr
##

#Return       Canvas placeholder with dimensions ##

#Example
    SkCanvas canvas(10, 20);  // 10 units wide, 20 units high
    canvas.clipRect(SkRect::MakeXYWH(30, 40, 5, 10));  // clip is outside canvas' device
    SkDebugf("canvas %s empty\n", canvas.getDeviceClipBounds().isEmpty() ? "is" : "is not");

    #StdOut
        canvas is empty
    ##
##

#SeeAlso SkSurfaceProps SkPixelGeometry

##

# ------------------------------------------------------------------------------

#Method explicit SkCanvas(SkBaseDevice* device)

Construct a canvas that draws into device.
Used by child classes of SkCanvas.

#ToDo  Since SkBaseDevice is private, shouldn't this be private also? ##

#Param device   specifies a device for the canvas to draw into ##

#Return         Canvas that can be used to draw into device ##

#Example
#Error "Unsure how to create a meaningful example."
 SkPDFCanvas::SkPDFCanvas(const sk_sp<SkPDFDevice>& dev)
    : SkCanvas(dev.get()) {}
##

#ToDo either remove doc of figure out a way to fiddle it ##

##

# ------------------------------------------------------------------------------

#Method explicit SkCanvas(const SkBitmap& bitmap)

Construct a canvas that draws into bitmap.
Sets SkSurfaceProps::kLegacyFontHost_InitType in constructed Surface. 

Bitmap is copied so that subsequently editing bitmap will not affect
constructed Canvas.

May be deprecated in the future.

#ToDo Should be deprecated? ##

#Param bitmap   width, height, Image_Color_Type, Image_Alpha_Type, and pixel
                storage of Raster_Surface
##

#Return         Canvas that can be used to draw into bitmap ##

#Example
#Description
The actual output depends on the installed fonts.
##
    SkBitmap bitmap;
    // create a bitmap 5 wide and 11 high
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(5, 11));
    SkCanvas canvas(bitmap);
    canvas.clear(SK_ColorWHITE);  // white is unpremultiplied, in ARGB order
    SkPixmap pixmap;  // provides guaranteed access to the drawn pixels
    if (!canvas.peekPixels(&pixmap)) {
        SkDebugf("peekPixels should never fail.\n");
    }
    const SkPMColor* pixels = pixmap.addr32();  // points to top left of bitmap
    SkPMColor pmWhite = pixels[0];  // the premultiplied format may vary
    SkPaint paint;  // by default, draws black, 12 point text
    canvas.drawString("!", 1, 10, paint);  // 1 char at baseline (1, 10)
    for (int y = 0; y < bitmap.height(); ++y) {
        for (int x = 0; x < bitmap.width(); ++x) {
            SkDebugf("%c", *pixels++ == pmWhite ? '-' : 'x');
        }
        SkDebugf("\n");
    }

    #StdOut
    -----
    --x--
    --x--
    --x--
    --x--
    --x--
    --x--
    -----
    --x--
    --x--
    -----
    #StdOut ##
##

#ToDo incomplete ##

##

#EnumClass ColorBehavior

#Private
Android framework only.
##

#Code
    enum class ColorBehavior {
        kLegacy,
    };
##
#Const kLegacy 0
    Is a placeholder to allow specialized constructor; has no meaning.
##
##

#Method SkCanvas(const SkBitmap& bitmap, ColorBehavior behavior)

#Private
Android framework only.
##

#Param bitmap    specifies a bitmap for the canvas to draw into ##
#Param behavior  specializes this constructor; value is unused ##
#Return          Canvas that can be used to draw into bitmap ##

#NoExample
##
##

# ------------------------------------------------------------------------------

#Method SkCanvas(const SkBitmap& bitmap, const SkSurfaceProps& props)

Construct a canvas that draws into bitmap.
Use props to match the device characteristics, like LCD striping.

bitmap is copied so that subsequently editing bitmap will not affect
constructed Canvas.

#Param bitmap   width, height, Image_Color_Type, Image_Alpha_Type,
                and pixel storage of Raster_Surface 
##
#Param props    order and orientation of RGB striping; and whether to use
                device independent fonts
##

#Return         Canvas that can be used to draw into bitmap ##

#Example
#Description
The actual output depends on the installed fonts.
##
    SkBitmap bitmap;
    // create a bitmap 5 wide and 11 high
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(5, 11));
    SkCanvas canvas(bitmap, SkSurfaceProps(0, kUnknown_SkPixelGeometry));
    canvas.clear(SK_ColorWHITE);  // white is unpremultiplied, in ARGB order
    SkPixmap pixmap;  // provides guaranteed access to the drawn pixels
    if (!canvas.peekPixels(&pixmap)) {
        SkDebugf("peekPixels should never fail.\n");
    }
    const SkPMColor* pixels = pixmap.addr32();  // points to top left of bitmap
    SkPMColor pmWhite = pixels[0];  // the premultiplied format may vary
    SkPaint paint;  // by default, draws black, 12 point text
    canvas.drawString("!", 1, 10, paint);  // 1 char at baseline (1, 10)
    for (int y = 0; y < bitmap.height(); ++y) {
        for (int x = 0; x < bitmap.width(); ++x) {
            SkDebugf("%c", *pixels++ == pmWhite ? '-' : 'x');
        }
        SkDebugf("\n");
    }

    #StdOut
    -----
    ---x-
    ---x-
    ---x-
    ---x-
    ---x-
    ---x-
    -----
    ---x-
    ---x-
    -----
    #StdOut ##
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method virtual ~SkCanvas()

Draw saved layers, if any.
Free up resources used by Canvas.

#Example
#Description
Canvas offscreen draws into bitmap. saveLayerAlpha sets up an additional
drawing surface that blends with the bitmap. When offscreen goes out of
scope, offscreen destructor is called. The saved layer is restored, drawing
transparent letters.
##
void draw(SkCanvas* canvas) {
    SkBitmap bitmap;
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(200, 200));
    {
        SkCanvas offscreen(bitmap);
        SkPaint paint;
        paint.setTextSize(100);
        offscreen.drawString("ABC", 20, 160, paint);
        SkRect layerBounds = SkRect::MakeXYWH(32, 32, 192, 192);
        offscreen.saveLayerAlpha(&layerBounds, 128);
        offscreen.clear(SK_ColorWHITE);
        offscreen.drawString("DEF", 20, 160, paint);
    }
    canvas->drawBitmap(bitmap, 0, 0, nullptr);
}
##

#SeeAlso State_Stack

##

# ------------------------------------------------------------------------------

#Method SkMetaData& getMetaData()

Associates additional data with the canvas.
The storage is freed when Canvas is deleted.

#Return  storage that can be read from and written to ##

#Example
    const char* kHelloMetaData = "HelloMetaData";
    SkCanvas canvas;
    SkMetaData& metaData = canvas.getMetaData();
    SkDebugf("before: %s\n", metaData.findString(kHelloMetaData));
    metaData.setString(kHelloMetaData, "Hello!");
    SkDebugf("during: %s\n", metaData.findString(kHelloMetaData));
    metaData.removeString(kHelloMetaData);
    SkDebugf("after: %s\n", metaData.findString(kHelloMetaData));

    #StdOut
        before: (null)
        during: Hello!
        after: (null)
    #StdOut ##
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method SkImageInfo imageInfo() const

Returns Image_Info for Canvas. If Canvas is not associated with Raster_Surface or
GPU_Surface, returned Image_Color_Type is set to kUnknown_SkColorType.

#Return  dimensions and Image_Color_Type of Canvas ##

#Example
    SkCanvas emptyCanvas;
    SkImageInfo canvasInfo = emptyCanvas.imageInfo();
    SkImageInfo emptyInfo;
    SkDebugf("emptyInfo %c= canvasInfo\n", emptyInfo == canvasInfo ? '=' : '!');

    #StdOut
        emptyInfo == canvasInfo
    ##
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method bool getProps(SkSurfaceProps* props) const

If Canvas is associated with Raster_Surface or
GPU_Surface, copies Surface_Properties and returns true. Otherwise,
return false and leave props unchanged.

#Param props  storage for writable SkSurfaceProps ##

#Return  true if Surface_Properties was copied ##

#ToDo This seems old style. Deprecate? ##

#Example
    SkBitmap bitmap;
    SkCanvas canvas(bitmap, SkSurfaceProps(0, kRGB_V_SkPixelGeometry));
    SkSurfaceProps surfaceProps(0, kUnknown_SkPixelGeometry);
    SkDebugf("isRGB:%d\n", SkPixelGeometryIsRGB(surfaceProps.pixelGeometry()));
    if (!canvas.getProps(&surfaceProps)) {
        SkDebugf("getProps failed unexpectedly.\n");
    }
    SkDebugf("isRGB:%d\n", SkPixelGeometryIsRGB(surfaceProps.pixelGeometry()));

    #StdOut
        isRGB:0
        isRGB:1
    #StdOut ##
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void flush()

Triggers the immediate execution of all pending draw operations. 
If Canvas is associated with GPU_Surface, resolves all pending GPU operations.

#Example
#Error "haven't thought of a useful example to put here"
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method virtual SkISize getBaseLayerSize() const

Gets the size of the base or root layer in global canvas coordinates. The
origin of the base layer is always (0,0). The current drawable area may be
smaller (due to clipping or saveLayer).

#Return  integral width and height of base layer ##

#Example
    SkBitmap bitmap;
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(20, 30));
    SkCanvas canvas(bitmap, SkSurfaceProps(0, kUnknown_SkPixelGeometry));
    canvas.clipRect(SkRect::MakeWH(10, 40));
    SkIRect clipDeviceBounds = canvas.getDeviceClipBounds();
    if (clipDeviceBounds.isEmpty()) {
        SkDebugf("Empty clip bounds is unexpected!\n");
    }
    SkDebugf("clip=%d,%d\n", clipDeviceBounds.width(), clipDeviceBounds.height());
    SkISize baseLayerSize = canvas.getBaseLayerSize();
    SkDebugf("size=%d,%d\n", baseLayerSize.width(), baseLayerSize.height());

    #StdOut
        clip=10,30
        size=20,30
    ##
##

#ToDo is this the same as the width and height of surface? ##

##

# ------------------------------------------------------------------------------

#Method sk_sp<SkSurface> makeSurface(const SkImageInfo& info, const SkSurfaceProps* props = nullptr)

Creates Surface matching info and props, and associates it with Canvas.
Returns nullptr if no match found.

If props is nullptr, matches Surface_Properties in Canvas. If props is nullptr and Canvas
does not have Surface_Properties, creates Surface with default Surface_Properties.

#Param info  width, height, Image_Color_Type, Image_Alpha_Type, and Color_Space ##
#Param props  Surface_Properties to match; may be nullptr to match Canvas ##

#Return  Surface matching info and props, or nullptr if no match is available ##

#Example
    sk_sp<SkSurface> surface = SkSurface::MakeRasterN32Premul(5, 6);
    SkCanvas* smallCanvas = surface->getCanvas();
    SkImageInfo imageInfo = SkImageInfo::MakeN32Premul(3, 4);
    sk_sp<SkSurface> compatible = smallCanvas->makeSurface(imageInfo);
    SkDebugf("compatible %c= nullptr\n", compatible == nullptr ? '=' : '!');
    SkDebugf("size = %d, %d\n", compatible->width(), compatible->height());

    #StdOut
        compatible != nullptr
        size = 3, 4
    ##
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method virtual GrContext* getGrContext()

Returns GPU_Context of the GPU_Surface associated with Canvas.

#Return GPU_Context, if available; nullptr otherwise ##

#Example
void draw(SkCanvas* canvas) {
    if (canvas->getGrContext()) {
         canvas->clear(SK_ColorRED);
    } else {
         canvas->clear(SK_ColorBLUE);
    }
}
##

#ToDo fiddle should show both CPU and GPU out ##

##

# ------------------------------------------------------------------------------

#Method void* accessTopLayerPixels(SkImageInfo* info, size_t* rowBytes, SkIPoint* origin = NULL)

Returns the pixel base address, Image_Info, rowBytes, and origin if the pixels
can be read directly. The returned address is only valid
while Canvas is in scope and unchanged. Any Canvas call or Surface call
may invalidate the returned address and other returned values.

If pixels are inaccessible, info, rowBytes, and origin are unchanged.

#Param info      storage for writable pixels' Image_Info; may be nullptr ##
#Param rowBytes  storage for writable pixels' row bytes; may be nullptr ##
#Param origin    storage for Canvas top layer origin, its top left corner;
                 may be nullptr
##

#Return  Address of pixels, or nullptr if inaccessible ##

#Example
void draw(SkCanvas* canvas) {
    if (canvas->accessTopLayerPixels(nullptr, nullptr)) {
         canvas->clear(SK_ColorRED);
    } else {
         canvas->clear(SK_ColorBLUE);
    }
}
##

#Example
#Description
Draws "ABC" on the device. Then draws "DEF" in an offscreen layer, and reads the
offscreen to add a large dotted "DEF". Finally blends the offscreen with the
device. 

The offscreen and blended result appear on the CPU and GPU but the large dotted
"DEF" appear only on the CPU.
##
void draw(SkCanvas* canvas) {
  SkPaint paint;
  paint.setTextSize(100);
  canvas->drawString("ABC", 20, 160, paint);
  SkRect layerBounds = SkRect::MakeXYWH(32, 32, 192, 192);
  canvas->saveLayerAlpha(&layerBounds, 128);
  canvas->clear(SK_ColorWHITE);
  canvas->drawString("DEF", 20, 160, paint);
  SkImageInfo imageInfo;
  size_t rowBytes;
  SkIPoint origin;
  uint32_t* access = (uint32_t*) canvas->accessTopLayerPixels(&imageInfo, &rowBytes, &origin);
  if (access) {
    int h = imageInfo.height();
    int v = imageInfo.width();
    int rowWords = rowBytes / sizeof(uint32_t);
    for (int y = 0; y < h; ++y) {
        int newY = (y - h / 2) * 2 + h / 2;
        if (newY < 0 || newY >= h) {
            continue;
        }
        for (int x = 0; x < v; ++x) {
            int newX = (x - v / 2) * 2 + v / 2;
            if (newX < 0 || newX >= v) {
                continue;
            }
            if (access[y * rowWords + x] == SK_ColorBLACK) {
                access[newY * rowWords + newX] = SK_ColorGRAY;
            }
        }
    }

  }
  canvas->restore();
}
##

#ToDo there are no callers of this that I can find. Deprecate? ##
#ToDo fiddle should show both CPU and GPU out ##

##

# ------------------------------------------------------------------------------

#Method SkRasterHandleAllocator::Handle accessTopRasterHandle() const

Returns custom context that tracks the Matrix and Clip.

Use Raster_Handle_Allocator to blend Skia drawing with custom drawing, typically performed
by the host platform's user interface. This accessor returns the custom context generated by
SkRasterHandleAllocator::MakeCanvas, which creates a custom canvas with raster storage for
the drawing destination.

#Return  context of custom allocator ##

#Example
#Description
#ToDo ##
##
#Function
    static void DeleteCallback(void*, void* context) {
        delete (char*) context;
    }

    class CustomAllocator : public SkRasterHandleAllocator {
    public:
        bool allocHandle(const SkImageInfo& info, Rec* rec) override {
            char* context = new char[4]{'s', 'k', 'i', 'a'};
            rec->fReleaseProc = DeleteCallback;
            rec->fReleaseCtx = context;
            rec->fHandle = context;
            rec->fPixels = context;
            rec->fRowBytes = 4;
            return true;
        }

        void updateHandle(Handle handle, const SkMatrix& ctm, const SkIRect& clip_bounds) override {
            // apply canvas matrix and clip to custom environment
        }
    };

##
    void draw(SkCanvas* canvas) {
        const SkImageInfo info = SkImageInfo::MakeN32Premul(1, 1);
        std::unique_ptr<SkCanvas> c2 =
                SkRasterHandleAllocator::MakeCanvas(std::unique_ptr<CustomAllocator>(
                new CustomAllocator()), info);
        char* context = (char*) c2->accessTopRasterHandle();
        SkDebugf("context = %.4s\n", context);

    }
    #StdOut
        context = skia
    ##
    #ToDo skstd::make_unique could not be used because def is private -- note to fix in c++14? ##
##

#SeeAlso SkRasterHandleAllocator

##

# ------------------------------------------------------------------------------

#Method bool peekPixels(SkPixmap* pixmap)

Returns true if Canvas has direct access to its pixels.

Pixels are readable when Device is raster. Pixels are not readable when SkCanvas
is returned from GPU_Surface, returned by SkDocument::beginPage, returned by
SkPictureRecorder::beginRecording, or SkCanvas is the base of a utility class
like SkDumpCanvas.

pixmap pixel address is only valid while Canvas is in scope and unchanged. Any
Canvas or Surface call may invalidate the pixmap values.

#Param pixmap  storage for Canvas pixel state if Canvas pixels are readable;
               otherwise, ignored
##

#Return  true if Canvas has direct access to pixels ##

#Example
    SkPixmap pixmap;
    if (canvas->peekPixels(&pixmap)) {
        SkDebugf("width=%d height=%d\n", pixmap.bounds().width(), pixmap.bounds().height());
    }
    #StdOut
        width=256 height=256
    ##
##

##

# ------------------------------------------------------------------------------

#Method bool readPixels(const SkImageInfo& dstInfo, void* dstPixels, size_t dstRowBytes,
                    int srcX, int srcY)

Copies rectangle of pixels from Canvas into dstPixels, converting their
Image_Color_Type and Image_Alpha_Type. Pixels are readable when Device is
raster. Pixels are not readable when SkCanvas is returned from GPU_Surface,
returned by SkDocument::beginPage, returned by SkPictureRecorder::beginRecording,
or SkCanvas is the base of a utility class like SkDumpCanvas.

Pixel values are converted only if Canvas Image_Color_Type and Image_Alpha_Type
does not match dstInfo. Only pixels within the rectangle that intersect Canvas
pixels are copied. dstPixels outside the rectangle intersection are unchanged.

#Table
#Legend
# source rectangle # value ##
##
# left # srcX ##
# top # srcY ##
# width # dstInfo.width() ##
# height # dstInfo.height() ##
##

 #Table
#Legend
# canvas pixel bounds # value ##
##
# left # 0 ##
# top # 0 ##
# width # imageInfo().width() ##
# height # imageInfo().height() ##
##

Does not copy, and returns false if:

#List
# Source rectangle and canvas pixel bounds do not intersect. ##
# Canvas pixels could not be converted to dstInfo Image_Color_Type or dstInfo Image_Alpha_Type. ##
# Canvas pixels are not readable; for instance, Canvas is not raster, or is document-based. ##
# dstRowBytes is too small to contain one row of pixels. ##
##

#Param dstInfo  dimensions, Image_Color_Type, and Image_Alpha_Type of dstPixels ##
#Param dstPixels  storage for pixels, of size dstInfo.height() times dstRowBytes ##
#Param dstRowBytes  size of one destination row, dstInfo.width() times pixel size ##
#Param srcX  offset into readable pixels in x ##
#Param srcY  offset into readable pixels in y ##

#Return  true if pixels were copied ##

#Example
#Description
    Canvas returned by Raster_Surface has premultiplied pixel values.
    clear() takes unpremultiplied input with Color_Alpha equal 0x80
    and Color_RGB equal 0x55, 0xAA, 0xFF. Color_RGB is multipled by Color_Alpha
    to generate premultipled value 0x802B5580. readPixels converts pixel back
    to unpremultipled value 0x8056A9FF, introducing error.
##
    canvas->clear(0x8055aaff);
    for (SkAlphaType alphaType : { kPremul_SkAlphaType, kUnpremul_SkAlphaType } ) {
        uint32_t pixel = 0;
        SkImageInfo info = SkImageInfo::Make(1, 1, kBGRA_8888_SkColorType, alphaType);
        if (canvas->readPixels(info, &pixel, 4, 0, 0)) {
            SkDebugf("pixel = %08x\n", pixel);
        }
    }

    #StdOut
        pixel = 802b5580
        pixel = 8056a9ff
    ##
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method bool readPixels(const SkPixmap& pixmap, int srcX, int srcY)

Copies rectangle of pixels from Canvas into Pixmap, converting their
Image_Color_Type and Image_Alpha_Type. Pixels are readable when Device is raster.
Pixels are not readable when SkCanvas is returned from GPU_Surface, returned by
SkDocument::beginPage, returned by SkPictureRecorder::beginRecording,
or SkCanvas is the base of a utility class like SkDumpCanvas.

Pixel values are converted only if Canvas Image_Color_Type and Image_Alpha_Type
does not match bitmap Image_Info. Only Pixmap pixels within the rectangle that
intersect Canvas pixels are copied. Pixmap pixels outside the rectangle
intersection are unchanged.

#Table
#Legend
# source rectangle # value ##
##
# left # srcX ##
# top # srcY ##
# width # bitmap.width() ##
# height # bitmap.height() ##
##

 #Table
#Legend
# canvas pixel bounds # value ##
##
# left # 0 ##
# top # 0 ##
# width # imageInfo().width() ##
# height # imageInfo().height() ##
##

Does not copy, and returns false if:

#List
# Source rectangle and canvas pixel bounds do not intersect. ##
# Canvas pixels could not be converted to bitmap Image_Color_Type or bitmap Image_Alpha_Type. ##
# Canvas pixels are not readable; for instance, Canvas is not raster, or is document-based. ##
# bitmap pixels could not be allocated. ##
# Bitmap_Row_Bytes is too small to contain one row of pixels. ##
##

#Param pixmap  storage for pixels copied from Canvas ##
#Param srcX    offset into readable pixels in x ##
#Param srcY    offset into readable pixels in y ##

#Return  true if pixels were copied ##

#Example
void draw(SkCanvas* canvas) {
    canvas->clear(0x8055aaff);
    uint32_t pixels[1] = { 0 };
    SkPixmap pixmap(SkImageInfo::MakeN32Premul(1, 1), pixels, 4);
    canvas->readPixels(pixmap, 0, 0);
    SkDebugf("pixel = %08x\n", pixels[0]);
}
    #StdOut
        pixel = 802b5580
    ##
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method bool readPixels(const SkBitmap& bitmap, int srcX, int srcY)

Copies pixels enclosed by bitmap offset to (x, y) from Canvas into bitmap,
converting their Image_Color_Type and Image_Alpha_Type.
Pixels are readable when Device is raster. Pixels are not readable when SkCanvas
is returned from GPU_Surface, returned by SkDocument::beginPage, returned by
SkPictureRecorder::beginRecording, or SkCanvas is the base of a utility class
like SkDumpCanvas. Allocates pixel storage in bitmap if needed.

Pixel values are converted only if Canvas Image_Color_Type and Image_Alpha_Type
does not match bitmap Image_Info. Only pixels within the rectangle that intersect
Canvas pixels are copied. Bitamp pixels outside the rectangle intersection are
unchanged.

#Table
#Legend
# canvas pixel bounds # value ##
##
# left # 0 ##
# top # 0 ##
# width # imageInfo().width() ##
# height # imageInfo().height() ##
##

Does not copy, and returns false if:

#List
# Bounds formed by (x, y) and bitmap (width, height) and canvas pixel bounds do not intersect. ##
# Canvas pixels could not be converted to bitmap Image_Color_Type or bitmap Image_Alpha_Type. ##
# Canvas pixels are not readable; for instance, Canvas is not raster, or is document-based. ##
# bitmap pixels could not be allocated. ##
# Bitmap_Row_Bytes is too small to contain one row of pixels. ##
##

#Param bitmap  storage for pixels copied from Canvas ##
#Param srcX    offset into readable pixels in x ##
#Param srcY    offset into readable pixels in y ##

#Return  true if pixels were copied ##

#Example
void draw(SkCanvas* canvas) {
    canvas->clear(0x8055aaff);
    SkBitmap bitmap;
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(1, 1));
    canvas->readPixels(bitmap, 0, 0);
    SkDebugf("pixel = %08x\n", bitmap.getAddr32(0, 0)[0]);
}
    #StdOut
        pixel = 802b5580
    ##
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method bool writePixels(const SkImageInfo& info, const void* pixels, size_t rowBytes, int x, int y)

Copies to Canvas pixels, ignoring the Matrix and Clip, converting to match
info Image_Color_Type and info Image_Alpha_Type.

Pixel values are converted only if Canvas Image_Color_Type and Image_Alpha_Type
does not match info. Only pixels within the source rectangle that intersect
Canvas pixel bounds are copied. Canvas pixels outside the rectangle intersection
are unchanged.

#Table
#Legend
# source rectangle # value ##
##
# left # x ##
# top # y ##
# width # info.width() ##
# height # info.height() ##
##

 #Table
#Legend
# canvas pixel bounds # value ##
##
# left # 0 ##
# top # 0 ##
# width # imageInfo().width() ##
# height # imageInfo().height() ##
##

Does not copy, and returns false if:

#List
# Source rectangle and canvas pixel bounds do not intersect. ##
# pixels could not be converted to Canvas Image_Color_Type or Canvas Image_Alpha_Type. ##
# Canvas pixels are not writable; for instance, Canvas is document-based. ##
# rowBytes is too small to contain one row of pixels. ##
##

#Param info    dimensions, Image_Color_Type, and Image_Alpha_Type of pixels ##
#Param pixels  pixels to copy, of size info.height() times rowBytes ##
#Param rowBytes  offset from one row to the next, usually info.width() times pixel size ##
#Param x  offset into Canvas writable pixels in x ##
#Param y  offset into Canvas writable pixels in y ##

#Return  true if pixels were written to Canvas ##

#Example
    SkImageInfo imageInfo = SkImageInfo::MakeN32(256, 1, kPremul_SkAlphaType);
    for (int y = 0; y < 256; ++y) {
        uint32_t pixels[256];
        for (int x = 0; x < 256; ++x) {
            pixels[x] = SkColorSetARGB(x, x + y, x, x - y);
        }
        canvas->writePixels(imageInfo, &pixels, sizeof(pixels), 0, y);
    }
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method bool writePixels(const SkBitmap& bitmap, int x, int y)

Writes to Canvas pixels, ignoring the Matrix and Clip, converting to match
bitmap Image_Color_Type and bitmap Image_Alpha_Type.

Pixel values are converted only if Canvas Image_Color_Type and Image_Alpha_Type
does not match bitmap. Only pixels within the source rectangle that intersect
Canvas pixel bounds are copied. Canvas pixels outside the rectangle intersection
are unchanged.

#Table
#Legend
# source rectangle # value ##
##
# left # x ##
# top # y ##
# width # bitmap.width() ##
# height # bitmap.height() ##
##

 #Table
#Legend
# canvas pixel bounds # value ##
##
# left # 0 ##
# top # 0 ##
# width # imageInfo().width() ##
# height # imageInfo().height() ##
##

Does not copy, and returns false if:

#List
# Source rectangle and Canvas pixel bounds do not intersect. ##
# bitmap does not have allocated pixels. ##
# bitmap pixels could not be converted to Canvas Image_Color_Type or Canvas Image_Alpha_Type. ##
# Canvas pixels are not writable; for instance, Canvas is document-based. ##
# bitmap pixels are inaccessible; for instance, bitmap wraps a texture. ##
##

#Param bitmap  contains pixels copied to Canvas ##
#Param x       offset into Canvas writable pixels in x ##
#Param y       offset into Canvas writable pixels in y ##

#Return  true if pixels were written to Canvas ##

#Example
void draw(SkCanvas* canvas) {
    SkImageInfo imageInfo = SkImageInfo::MakeN32Premul(2, 2);
    SkBitmap bitmap;
    bitmap.setInfo(imageInfo);
    uint32_t pixels[4];
    bitmap.setPixels(pixels);
    for (int y = 0; y < 256; y += 2) {
        for (int x = 0; x < 256;  x += 2) {
            pixels[0] = SkColorSetRGB(x, y, x | y);
            pixels[1] = SkColorSetRGB(x ^ y, y, x);
            pixels[2] = SkColorSetRGB(x, x & y, y);
            pixels[3] = SkColorSetRGB(~x, ~y, x);
            canvas->writePixels(bitmap, x, y);
        }
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------
#Topic State_Stack

Canvas maintains a stack of state that allows hierarchical drawing, commonly used
to implement windows and views. The initial state has an identity matrix and and
an infinite clip. Even with a wide-open clip, drawing is constrained by the
bounds of the Canvas Surface or Device.

Canvas savable state consists of Clip, Matrix, and Draw_Filter.
Clip describes the area that may be drawn to.
Matrix transforms the geometry.
Draw_Filter (deprecated on most platforms) modifies the paint before drawing.

save(), saveLayer, saveLayerPreserveLCDTextRequests, and saveLayerAlpha
save state and return the depth of the stack.

restore(), restoreToCount, and ~SkCanvas() revert state to its value when saved.

Each state on the stack intersects Clip with the previous Clip,
and concatenates Matrix with the previous Matrix.
The intersected Clip makes the drawing area the same or smaller;
the concatenated Matrix may move the origin and potentially scale or rotate
the coordinate space.

Canvas does not require balancing the state stack but it is a good idea
to do so. Calling save() without restore() will eventually cause Skia to fail;
mismatched save() and restore() create hard to find bugs.

It is not possible to use state to draw outside of the clip defined by the
previous state.

#Example
#Description
Draw to ever smaller clips; then restore drawing to full canvas.
Note that the second clipRect is not permitted to enlarge Clip.
##
#Height 160
void draw(SkCanvas* canvas) {
    SkPaint paint;
    canvas->save();                             // records stack depth to restore  
    canvas->clipRect(SkRect::MakeWH(100, 100)); // constrains drawing to clip
    canvas->clear(SK_ColorRED);                 // draws to limit of clip
    canvas->save();                             // records stack depth to restore 
    canvas->clipRect(SkRect::MakeWH(50, 150));  // Rect below 100 is ignored
    canvas->clear(SK_ColorBLUE);                // draws to smaller clip
    canvas->restore();                          // enlarges clip
    canvas->drawLine(20, 20, 150, 150, paint);  // line below 100 is not drawn
    canvas->restore();                          // enlarges clip
    canvas->drawLine(150, 20, 50, 120, paint);  // line below 100 is drawn
}
## 

Each Clip uses the current Matrix for its coordinates.

#Example
#Description
While clipRect is given the same rectangle twice, Matrix makes the second
clipRect draw at half the size of the first.
##
#Height 128
void draw(SkCanvas* canvas) {
    canvas->clipRect(SkRect::MakeWH(100, 100));
    canvas->clear(SK_ColorRED);
    canvas->scale(.5, .5);
    canvas->clipRect(SkRect::MakeWH(100, 100));
    canvas->clear(SK_ColorBLUE);
}
##

#SeeAlso save() saveLayer saveLayerPreserveLCDTextRequests saveLayerAlpha restore() restoreToCount

#Method int save()

Saves Matrix, Clip, and Draw_Filter (Draw_Filter deprecated on most platforms).
Calling restore() discards changes to Matrix, Clip, and Draw_Filter,
restoring the Matrix, Clip, and Draw_Filter to their state when save() was called.

Matrix may be changed by translate(), scale(), rotate(), skew(), concat(), setMatrix,
and resetMatrix. Clip may be changed by clipRect, clipRRect, clipPath, clipRegion.

Saved Canvas state is put on a stack; multiple calls to save() should be balance
by an equal number of calls to restore().

Call restoreToCount with result to restore this and subsequent saves.

#Return depth of saved stack ##

#Example
#Description 
The black square is translated 50 pixels down and to the right.
Restoring Canvas state removes translate() from Canvas stack;
the red square is not translated, and is drawn at the origin.
##
#Height 100
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkRect rect = { 0, 0, 25, 25 };
    canvas->drawRect(rect, paint);
    canvas->save();
    canvas->translate(50, 50);
    canvas->drawRect(rect, paint);
    canvas->restore();
    paint.setColor(SK_ColorRED);
    canvas->drawRect(rect, paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------
#Subtopic Layer

Layer allocates a temporary offscreen Bitmap to draw into. When the drawing is
complete, the Bitmap is drawn into the Canvas. 

Layer is saved in a stack along with other saved state. When state with a Layer
is restored, the offscreen Bitmap is drawn into the previous layer.

Layer may be initialized with the contents of the previous layer. When Layer is
restored, its Bitmap can be modified by Paint passed to Layer to apply
Color_Alpha, Color_Filter, Image_Filter, and Blend_Mode.

#Method int saveLayer(const SkRect* bounds, const SkPaint* paint)

Saves Matrix, Clip, and Draw_Filter (Draw_Filter deprecated on most platforms),
and allocates an offscreen Bitmap for subsequent drawing.
Calling restore() discards changes to Matrix, Clip, and Draw_Filter,
and draws the offscreen bitmap.

Matrix may be changed by translate(), scale(), rotate(), skew(), concat(),
setMatrix, and resetMatrix. Clip may be changed by clipRect, clipRRect, 
clipPath, clipRegion.

Rect bounds suggests but does not define the offscreen size. To clip drawing to
a specific rectangle, use clipRect.

Optional Paint paint applies Color_Alpha, Color_Filter, Image_Filter, and
Blend_Mode when restore() is called.

Call restoreToCount with returned value to restore this and subsequent saves.

#Param bounds  hint to limit the size of the offscreen; may be nullptr ##
#Param paint   graphics state for offscreen; may be nullptr ##

#Return        depth of saved stack ##

#Example
#Description
Rectangles are blurred by Image_Filter when restore() draws offscreen to main
Canvas.
##
#Height 128
void draw(SkCanvas* canvas) {
    SkPaint paint, blur;
    blur.setImageFilter(SkImageFilter::MakeBlur(3, 3, nullptr));
    canvas->saveLayer(nullptr, &blur);
    SkRect rect = { 25, 25, 50, 50};
    canvas->drawRect(rect, paint);
    canvas->translate(50, 50);
    paint.setColor(SK_ColorRED);
    canvas->drawRect(rect, paint);
    canvas->restore();
}
##

#ToDo incomplete ##

##

#Method int saveLayer(const SkRect& bounds, const SkPaint* paint) 

Saves Matrix, Clip, and Draw_Filter (Draw_Filter deprecated on most platforms),
and allocates an offscreen Bitmap for subsequent drawing.
Calling restore() discards changes to Matrix, Clip, and Draw_Filter,
and draws the offscreen Bitmap.

Matrix may be changed by translate(), scale(), rotate(), skew(), concat(),
setMatrix, and resetMatrix. Clip may be changed by clipRect, clipRRect,
clipPath, clipRegion.

Rect bounds suggests but does not define the offscreen size. To clip drawing to
a specific rectangle, use clipRect.

Optional Paint paint applies Color_Alpha, Color_Filter, Image_Filter, and
Blend_Mode when restore() is called.

Call restoreToCount with returned value to restore this and subsequent saves.

#Param bounds  hint to limit the size of the offscreen; may be nullptr ##
#Param paint   graphics state for offscreen; may be nullptr ##

#Return        depth of saved stack ##

#Example
#Description
Rectangles are blurred by Image_Filter when restore() draws offscreen to main Canvas.
The red rectangle is clipped; it does not fully fit on the offscreen Canvas. 
Image_Filter blurs past edge of offscreen so red rectangle is blurred on all sides.
##
#Height 128
void draw(SkCanvas* canvas) {
    SkPaint paint, blur;
    blur.setImageFilter(SkImageFilter::MakeBlur(3, 3, nullptr));
    canvas->saveLayer(SkRect::MakeWH(90, 90), &blur);
    SkRect rect = { 25, 25, 50, 50};
    canvas->drawRect(rect, paint);
    canvas->translate(50, 50);
    paint.setColor(SK_ColorRED);
    canvas->drawRect(rect, paint);
    canvas->restore();
}
##

#ToDo incomplete ##

##

#Method int saveLayerPreserveLCDTextRequests(const SkRect* bounds, const SkPaint* paint)

Saves Matrix, Clip, and Draw_Filter (Draw_Filter deprecated on most platforms),
and allocates an offscreen bitmap for subsequent drawing.
LCD_Text is preserved when the offscreen is drawn to the prior layer.

Calling restore() discards changes to Matrix, Clip, and Draw_Filter,
and draws the offscreen bitmap.

Matrix may be changed by translate(), scale(), rotate(), skew(), concat(),
setMatrix, and resetMatrix. Clip may be changed by clipRect, clipRRect,
clipPath, clipRegion.
  
Rect bounds suggests but does not define the offscreen size. To clip drawing to
a specific rectangle, use clipRect.

Optional Paint paint applies Color_Alpha, Color_Filter, Image_Filter, and
Blend_Mode when restore() is called.

Call restoreToCount with returned value to restore this and subsequent saves.

Draw text on an opaque background so that LCD_Text blends correctly with the
prior layer. LCD_Text drawn on a background with transparency may result in
incorrect banding.

#Param bounds  hint to limit the size of the offscreen; may be nullptr ##
#Param paint   graphics state for offscreen; may be nullptr ##

#Return        depth of saved stack ##

#Example
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setLCDRenderText(true);
    paint.setTextSize(20);
    for (auto preserve : { false, true } ) {
        preserve ? canvas->saveLayerPreserveLCDTextRequests(nullptr, nullptr)
                 : canvas->saveLayer(nullptr, nullptr);
        SkPaint p;
        p.setColor(SK_ColorWHITE);
        // Comment out the next line to draw on a non-opaque background.
        canvas->drawRect(SkRect::MakeLTRB(25, 40, 200, 70), p);
        canvas->drawString("Hamburgefons", 30, 60, paint);

        p.setColor(0xFFCCCCCC);
        canvas->drawRect(SkRect::MakeLTRB(25, 70, 200, 100), p);
        canvas->drawString("Hamburgefons", 30, 90, paint);

        canvas->restore();
        canvas->translate(0, 80);
    }
    ##

#ToDo incomplete ##

##

#Method int saveLayerAlpha(const SkRect* bounds, U8CPU alpha)

Saves Matrix, Clip, and Draw_Filter (Draw_Filter deprecated on most platforms),
and allocates an offscreen bitmap for subsequent drawing.

Calling restore() discards changes to Matrix, Clip, and Draw_Filter,
and blends the offscreen bitmap with alpha opacity onto the prior layer.

Matrix may be changed by translate(), scale(), rotate(), skew(), concat(),
setMatrix, and resetMatrix. Clip may be changed by clipRect, clipRRect,
clipPath, clipRegion.

Rect bounds suggests but does not define the offscreen size. To clip drawing to
a specific rectangle, use clipRect.

alpha of zero is fully transparent, 255 is fully opaque.

Call restoreToCount with returned value to restore this and subsequent saves.

#Param bounds  hint to limit the size of the offscreen; may be nullptr ##
#Param alpha   opacity of the offscreen ##

#Return  depth of saved stack ##

#Example
    SkPaint paint;
    paint.setColor(SK_ColorRED);
    canvas->drawCircle(50, 50, 50, paint);
    canvas->saveLayerAlpha(nullptr, 128);
    paint.setColor(SK_ColorBLUE);
    canvas->drawCircle(100, 50, 50, paint);
    paint.setColor(SK_ColorGREEN);
    paint.setAlpha(128);
    canvas->drawCircle(75, 90, 50, paint);
    canvas->restore();
##

#ToDo incomplete ##

##

#Enum

#Code
    enum {
        kIsOpaque_SaveLayerFlag = 1 << 0,
        kPreserveLCDText_SaveLayerFlag = 1 << 1,
        kInitWithPrevious_SaveLayerFlag = 1 << 2,
        kDontClipToLayer_Legacy_SaveLayerFlag = kDontClipToLayer_PrivateSaveLayerFlag,
    };

    typedef uint32_t SaveLayerFlags;
##

SaveLayerFlags provides options that may be used in any combination in SaveLayerRec,
defining how the offscreen allocated by saveLayer operates.

#Const kIsOpaque_SaveLayerFlag 1
  Creates offscreen without transparency. Flag is ignored if layer Paint contains
  Image_Filter or Color_Filter.
##

#Const kPreserveLCDText_SaveLayerFlag 2
  Creates offscreen for LCD text. Flag is ignored if layer Paint contains
  Image_Filter or Color_Filter.
##

#Const kInitWithPrevious_SaveLayerFlag 4
  Initializes offscreen with the contents of the previous layer.
##

#Const kDontClipToLayer_Legacy_SaveLayerFlag 0x80000000
#Private
  to be deprecated: bug.skia.org/2440
##
  Only present on Android.
  Skips setting a clip to the layer bounds. 
##

#Example
#Height 160
#Description
Canvas layer captures red and blue circles scaled up by four.
scalePaint blends offscreen back with transparency. 
##
void draw(SkCanvas* canvas) {
    SkPaint redPaint, bluePaint, scalePaint;
    redPaint.setColor(SK_ColorRED);
    canvas->drawCircle(21, 21, 8, redPaint);
    bluePaint.setColor(SK_ColorBLUE);
    canvas->drawCircle(31, 21, 8, bluePaint);
    SkMatrix matrix;
    matrix.setScale(4, 4);
    scalePaint.setAlpha(0x40);
    scalePaint.setImageFilter(
            SkImageFilter::MakeMatrixFilter(matrix, kNone_SkFilterQuality, nullptr));
    SkCanvas::SaveLayerRec saveLayerRec(nullptr, &scalePaint,
            SkCanvas::kInitWithPrevious_SaveLayerFlag); 
    canvas->saveLayer(saveLayerRec);
    canvas->restore();
}
##

#ToDo incomplete ##

#Enum ##

#Struct SaveLayerRec

#Code
    struct SaveLayerRec {
        SaveLayerRec*(...

        const SkRect*           fBounds;
        const SkPaint*          fPaint;
        const SkImageFilter*    fBackdrop;
        SaveLayerFlags          fSaveLayerFlags;
    };
##

SaveLayerRec contains the state used to create the layer offscreen. 

#Member const SkRect*           fBounds
    fBounds is used as a hint to limit the size of the offscreen; may be nullptr.
    fBounds suggests but does not define the offscreen size. To clip drawing to
    a specific rectangle, use clipRect.
##

#Member const SkPaint*          fPaint
    fPaint modifies how the offscreen overlays the prior layer; may be nullptr.
    Color_Alpha, Blend_Mode, Color_Filter, Draw_Looper, Image_Filter, and
    Mask_Filter affect the offscreen draw.
##

#Member const SkImageFilter*    fBackdrop
    fBackdrop applies Image_Filter to the prior layer when copying to the layer
    offscreen; may be nullptr. Use kInitWithPrevious_SaveLayerFlag to copy the
    prior layer without an Image_Filter.
##

#Member const SkImage*          fClipMask
  restore() clips the layer offscreen by the alpha channel of fClipMask when
  the offscreen is copied to Device. fClipMask may be nullptr.    .
##

#Member const SkMatrix*         fClipMatrix
  fClipMatrix transforms fClipMask before it clips the layer offscreen. If 
  fClipMask describes a translucent gradient, it may be scaled and rotated
  without introducing artifacts. fClipMatrix may be nullptr.
##

#Member SaveLayerFlags          fSaveLayerFlags
    fSaveLayerFlags are used to create layer offscreen without transparency,
    create layer offscreen for LCD text, and to create layer offscreen with the
    contents of the previous layer.
##

#Example
#Height 160
#Description
Canvas layer captures a red anti-aliased circle and a blue aliased circle scaled
up by four. After drawing another unscaled red circle on top, the offscreen is
transferred to the main canvas. 
##
void draw(SkCanvas* canvas) {
    SkPaint redPaint, bluePaint;
    redPaint.setAntiAlias(true);
    redPaint.setColor(SK_ColorRED);
    canvas->drawCircle(21, 21, 8, redPaint);
    bluePaint.setColor(SK_ColorBLUE);
    canvas->drawCircle(31, 21, 8, bluePaint);
    SkMatrix matrix;
    matrix.setScale(4, 4);
    auto scaler = SkImageFilter::MakeMatrixFilter(matrix, kNone_SkFilterQuality, nullptr);
    SkCanvas::SaveLayerRec saveLayerRec(nullptr, nullptr, scaler.get(), 0); 
    canvas->saveLayer(saveLayerRec);
    canvas->drawCircle(125, 85, 8, redPaint);
    canvas->restore();
}
##

#Method SaveLayerRec()

Sets fBounds, fPaint, and fBackdrop to nullptr. Clears fSaveLayerFlags.

#Return  empty SaveLayerRec ##

#Example
    SkCanvas::SaveLayerRec rec1;
    rec1.fSaveLayerFlags = SkCanvas::kIsOpaque_SaveLayerFlag;
    SkCanvas::SaveLayerRec rec2(nullptr, nullptr, SkCanvas::kIsOpaque_SaveLayerFlag);
    SkDebugf("rec1 %c= rec2\n", rec1.fBounds == rec2.fBounds
            && rec1.fPaint == rec2.fPaint
            && rec1.fBackdrop == rec2.fBackdrop
            && rec1.fSaveLayerFlags == rec2.fSaveLayerFlags ? '=' : '!');
    #StdOut
        rec1 == rec2
    ##
##

##

#Method SaveLayerRec(const SkRect* bounds, const SkPaint* paint, SaveLayerFlags saveLayerFlags = 0)

Sets fBounds, fPaint, and fSaveLayerFlags; sets fBackdrop to nullptr.

#Param bounds  offscreen dimensions; may be nullptr ##
#Param paint  applied to offscreen when overlaying prior layer; may be nullptr ##
#Param saveLayerFlags  SaveLayerRec options to modify offscreen ##

#Return  SaveLayerRec with empty backdrop ##

#Example
    SkCanvas::SaveLayerRec rec1;
    SkCanvas::SaveLayerRec rec2(nullptr, nullptr);
    SkDebugf("rec1 %c= rec2\n", rec1.fBounds == rec2.fBounds
            && rec1.fPaint == rec2.fPaint
            && rec1.fBackdrop == rec2.fBackdrop
            && rec1.fSaveLayerFlags == rec2.fSaveLayerFlags ? '=' : '!');
    #StdOut
        rec1 == rec2
    ##
##

##

#Method SaveLayerRec(const SkRect* bounds, const SkPaint* paint, const SkImageFilter* backdrop,
                     SaveLayerFlags saveLayerFlags)

Sets fBounds, fPaint, fBackdrop, and fSaveLayerFlags.

#Param bounds          offscreen dimensions; may be nullptr ##
#Param paint           applied to offscreen when overlaying prior layer;
                       may be nullptr
##
#Param backdrop        prior layer copied to offscreen with Image_Filter;
                       may be nullptr
##
#Param saveLayerFlags  SaveLayerRec options to modify offscreen ##

#Return  SaveLayerRec fully specified ##

#Example
    SkCanvas::SaveLayerRec rec1;
    SkCanvas::SaveLayerRec rec2(nullptr, nullptr, nullptr, 0);
    SkDebugf("rec1 %c= rec2\n", rec1.fBounds == rec2.fBounds
            && rec1.fPaint == rec2.fPaint
            && rec1.fBackdrop == rec2.fBackdrop
            && rec1.fSaveLayerFlags == rec2.fSaveLayerFlags ? '=' : '!');
    #StdOut
        rec1 == rec2
    ##
##

##

#Method SaveLayerRec(const SkRect* bounds, const SkPaint* paint, const SkImageFilter* backdrop,
                     const SkImage* clipMask, const SkMatrix* clipMatrix,
                     SaveLayerFlags saveLayerFlags)

#Experimental
Not ready for general use.
##

Sets fBounds, fPaint, fBackdrop, fClipMask, fClipMatrix, and fSaveLayerFlags.
clipMatrix uses alpha channel of image, transformed by clipMatrix, to clip layer
when drawn to Canvas.

Implementation is incomplete; has no effect if Device is GPU-backed.

#Param bounds          offscreen dimensions; may be nullptr ##
#Param paint           graphics state applied to offscreen when overlaying prior
                       layer; may be nullptr
##
#Param backdrop        prior layer copied to offscreen with Image_Filter;
                       may be nullptr
##
#Param clipMask        clip applied to layer; may be nullptr ##
#Param clipMatrix      matrix applied to clipMask; may be nullptr to use
                       identity matrix 
##
#Param saveLayerFlags  SaveLayerRec options to modify offscreen ##

#Return                SaveLayerRec fully specified ##

#ToDo  incomplete ##

##

#Struct ##

#Method int saveLayer(const SaveLayerRec& layerRec)

Saves Matrix, Clip, and Draw_Filter (Draw_Filter deprecated on most platforms),
and allocates an offscreen bitmap for subsequent drawing.

Calling restore() discards changes to Matrix, Clip, and Draw_Filter,
and blends the offscreen bitmap with alpha opacity onto the prior layer.

Matrix may be changed by translate(), scale(), rotate(), skew(), concat(),
setMatrix, and resetMatrix. Clip may be changed by clipRect, clipRRect,
clipPath, clipRegion.

SaveLayerRec contains the state used to create the layer offscreen.

Call restoreToCount with returned value to restore this and subsequent saves.

#Param layerRec  offscreen state ##

#Return          depth of save state stack ##

#Example
#Description
The example draws an image, and saves it into a layer with kInitWithPrevious_SaveLayerFlag.
Next it punches a hole in the layer and restore with SkBlendMode::kPlus.
Where the layer was cleared, the original image will draw unchanged.
Outside of the circle the mandrill is brightened.
##
    #Image 3
    // sk_sp<SkImage> image = GetResourceAsImage("mandrill_256.png");
    canvas->drawImage(image, 0, 0, nullptr);
    SkCanvas::SaveLayerRec rec;
    SkPaint paint;
    paint.setBlendMode(SkBlendMode::kPlus);
    rec.fSaveLayerFlags = SkCanvas::kInitWithPrevious_SaveLayerFlag;
    rec.fPaint = &paint;
    canvas->saveLayer(rec);
    paint.setBlendMode(SkBlendMode::kClear);
    canvas->drawCircle(128, 128, 96, paint);
    canvas->restore();
##

#ToDo above example needs to replace GetResourceAsImage with way to select image in fiddle ##

##

#Subtopic Layer ##

# ------------------------------------------------------------------------------

#Method void restore()

Removes changes to Matrix, Clip, and Draw_Filter since Canvas state was
last saved. The state is removed from the stack. 

Does nothing if the stack is empty. 

#Example
void draw(SkCanvas* canvas) {
    SkCanvas simple;
    SkDebugf("depth = %d\n", simple.getSaveCount());
    simple.restore();
    SkDebugf("depth = %d\n", simple.getSaveCount());
}
##

##

# ------------------------------------------------------------------------------

#Method int getSaveCount() const

Returns the number of saved states, each containing: Matrix, Clip, and Draw_Filter.
Equals the number of save() calls less the number of restore() calls plus one. 
The save count of a new canvas is one.

#Return  depth of save state stack ##

#Example
void draw(SkCanvas* canvas) {
    SkCanvas simple;
    SkDebugf("depth = %d\n", simple.getSaveCount());
    simple.save();
    SkDebugf("depth = %d\n", simple.getSaveCount());
    simple.restore();
    SkDebugf("depth = %d\n", simple.getSaveCount());
}
#StdOut
depth = 1
depth = 2
depth = 1
##
##

##

# ------------------------------------------------------------------------------

#Method void restoreToCount(int saveCount)

Restores state to Matrix, Clip, and Draw_Filter values when save(), saveLayer,
saveLayerPreserveLCDTextRequests, or saveLayerAlpha returned saveCount.

Does nothing if saveCount is greater than state stack count. 
Restores state to initial values if saveCount is less than or equal to one.

#Param saveCount    depth of state stack to restore ##

#Example
void draw(SkCanvas* canvas) {
    SkDebugf("depth = %d\n", canvas->getSaveCount());
    canvas->save();
    canvas->save();
    SkDebugf("depth = %d\n", canvas->getSaveCount());
    canvas->restoreToCount(0);
    SkDebugf("depth = %d\n", canvas->getSaveCount());
}
#StdOut
depth = 1
depth = 3
depth = 1
##
##

##

#Topic State_Stack ##

# ------------------------------------------------------------------------------
#Topic Matrix

#Method void translate(SkScalar dx, SkScalar dy)

Translate Matrix by dx along the x-axis and dy along the y-axis.

Mathematically, replace Matrix with a translation matrix
pre-multiplied with Matrix. 

This has the effect of moving the drawing by (dx, dy) before transforming
the result with Matrix.

#Param  dx   distance to translate in x ##
#Param  dy   distance to translate in y ##

#Example
#Height 128
#Description
scale() followed by translate() produces different results from translate() followed
by scale(). 

The blue stroke follows translate of (50, 50); a black
fill follows scale of (2, 1/2.f). After restoring the clip, which resets 
Matrix, a red frame follows the same scale of (2, 1/2.f); a gray fill
follows translate of (50, 50).
##
void draw(SkCanvas* canvas) {
    SkPaint filledPaint;
    SkPaint outlinePaint;
    outlinePaint.setStyle(SkPaint::kStroke_Style);
    outlinePaint.setColor(SK_ColorBLUE);
    canvas->save();
    canvas->translate(50, 50);
    canvas->drawCircle(28, 28, 15, outlinePaint);  // blue center: (50+28, 50+28)
    canvas->scale(2, 1/2.f);
    canvas->drawCircle(28, 28, 15, filledPaint);   // black center: (50+(28*2), 50+(28/2))
    canvas->restore();
    filledPaint.setColor(SK_ColorGRAY);
    outlinePaint.setColor(SK_ColorRED);
    canvas->scale(2, 1/2.f);
    canvas->drawCircle(28, 28, 15, outlinePaint);  // red center: (28*2, 28/2)
    canvas->translate(50, 50);
    canvas->drawCircle(28, 28, 15, filledPaint);   // gray center: ((50+28)*2, (50+28)/2)
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void scale(SkScalar sx, SkScalar sy)

Scale Matrix by sx on the x-axis and sy on the y-axis.

Mathematically, replace Matrix with a scale matrix
pre-multiplied with Matrix. 

This has the effect of scaling the drawing by (sx, sy) before transforming
the result with Matrix.

#Param  sx   amount to scale in x ##
#Param  sy   amount to scale in y ##

#Example
#Height 160
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkRect rect = { 10, 20, 60, 120 };
    canvas->translate(20, 20);
    canvas->drawRect(rect, paint);
    canvas->scale(2, .5f);
    paint.setColor(SK_ColorGRAY);
    canvas->drawRect(rect, paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void rotate(SkScalar degrees)

Rotate Matrix by degrees. Positive degrees rotates clockwise.

Mathematically, replace Matrix with a rotation matrix
pre-multiplied with Matrix. 

This has the effect of rotating the drawing by degrees before transforming
the result with Matrix.

#Param  degrees  amount to rotate, in degrees ##

#Example
#Description
Draw clock hands at time 5:10. The hour hand and minute hand point up and
are rotated clockwise.
##
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setStyle(SkPaint::kStroke_Style);
    canvas->translate(128, 128);
    canvas->drawCircle(0, 0, 60, paint);
    canvas->save();
    canvas->rotate(10 * 360 / 60);   // 10 minutes of 60 scaled to 360 degrees
    canvas->drawLine(0, 0, 0, -50, paint); 
    canvas->restore();
    canvas->rotate((5 + 10.f/60) * 360 / 12); // 5 and 10/60 hours of 12 scaled to 360 degrees
    canvas->drawLine(0, 0, 0, -30, paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void rotate(SkScalar degrees, SkScalar px, SkScalar py)

Rotate Matrix by degrees about a point at (px, py). Positive degrees rotates
clockwise.

Mathematically, construct a rotation matrix. Pre-multiply the rotation matrix by
a translation matrix, then replace Matrix with the resulting matrix
pre-multiplied with Matrix. 

This has the effect of rotating the drawing about a given point before
transforming the result with Matrix.

#Param  degrees  amount to rotate, in degrees ##
#Param  px  x-coordinate of the point to rotate about ##
#Param  py  y-coordinate of the point to rotate about ##

#Example
#Height 192
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setTextSize(96);
    canvas->drawString("A1", 130, 100, paint);
    canvas->rotate(180, 130, 100);
    canvas->drawString("A1", 130, 100, paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void skew(SkScalar sx, SkScalar sy)

Skew Matrix by sx on the x-axis and sy on the y-axis. A positive value of sx
skews the drawing right as y increases; a positive value of sy skews the drawing
down as x increases.

Mathematically, replace Matrix with a skew matrix pre-multiplied with Matrix. 

This has the effect of skewing the drawing by (sx, sy) before transforming
the result with Matrix.

#Param  sx   amount to skew in x ##
#Param  sy   amount to skew in y ##

#Example
    #Description 
        Black text mimics an oblique text style by using a negative skew in x that
        shifts the geometry to the right as the y values decrease.
        Red text uses a positive skew in y to shift the geometry down as the x values
        increase.
        Blue text combines x and y skew to rotate and scale.
    ##
    SkPaint paint;
    paint.setTextSize(128);
    canvas->translate(30, 130);
    canvas->save();
    canvas->skew(-.5, 0);
    canvas->drawString("A1", 0, 0, paint);
    canvas->restore();
    canvas->save();
    canvas->skew(0, .5);
    paint.setColor(SK_ColorRED);
    canvas->drawString("A1", 0, 0, paint);
    canvas->restore();
    canvas->skew(-.5, .5);
    paint.setColor(SK_ColorBLUE);
    canvas->drawString("A1", 0, 0, paint);
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void concat(const SkMatrix& matrix)

Replace Matrix with matrix pre-multiplied with existing Matrix.

This has the effect of transforming the drawn geometry by matrix, before
transforming the result with existing Matrix.

#Param  matrix   matrix to pre-multiply with existing Matrix ##

#Example
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setTextSize(80);
    paint.setTextScaleX(.3);
    SkMatrix matrix;
    SkRect rect[2] = {{ 10, 20, 90, 110 }, { 40, 130, 140, 180 }};
    matrix.setRectToRect(rect[0], rect[1], SkMatrix::kFill_ScaleToFit);
    canvas->drawRect(rect[0], paint);
    canvas->drawRect(rect[1], paint);
    paint.setColor(SK_ColorWHITE);
    canvas->drawString("Here", rect[0].fLeft + 10, rect[0].fBottom - 10, paint);
    canvas->concat(matrix);
    canvas->drawString("There", rect[0].fLeft + 10, rect[0].fBottom - 10, paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void setMatrix(const SkMatrix& matrix)

Replace Matrix with matrix.
Unlike concat(), any prior matrix state is overwritten.

#Param  matrix  matrix to copy, replacing existing Matrix ##

#Example
#Height 128
void draw(SkCanvas* canvas) {
    SkPaint paint;
    canvas->scale(4, 6);
    canvas->drawString("truth", 2, 10, paint);
    SkMatrix matrix;
    matrix.setScale(2.8f, 6);
    canvas->setMatrix(matrix);
    canvas->drawString("consequences", 2, 20, paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void resetMatrix()

Sets Matrix to the identity matrix.
Any prior matrix state is overwritten.

#Example
#Height 128
void draw(SkCanvas* canvas) {
    SkPaint paint;
    canvas->scale(4, 6);
    canvas->drawString("truth", 2, 10, paint);
    canvas->resetMatrix();
    canvas->scale(2.8f, 6);
    canvas->drawString("consequences", 2, 20, paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method const SkMatrix& getTotalMatrix() const

Returns Matrix.
This does not account for translation by Device or Surface.

#Return Matrix in Canvas ##

#Example
    SkDebugf("isIdentity %s\n", canvas->getTotalMatrix().isIdentity() ? "true" : "false");
    #StdOut
        isIdentity true
    ##
##

#ToDo incomplete ##

##

#Topic Matrix ##

# ------------------------------------------------------------------------------
#Topic Clip

Clip is built from a stack of clipping paths. Each Path in the
stack can be constructed from one or more Path_Contour elements. The 
Path_Contour may be composed of any number of Path_Verb segments. Each
Path_Contour forms a closed area; Path_Fill_Type defines the area enclosed
by Path_Contour.

Clip stack of Path elements successfully restrict the Path area. Each
Path is transformed by Matrix, then intersected with or subtracted from the 
prior Clip to form the replacement Clip. Use SkClipOp::kDifference
to subtract Path from Clip; use SkClipOp::kIntersect to intersect Path
with Clip.

A clipping Path may be anti-aliased; if Path, after transformation, is
composed of horizontal and vertical lines, clearing Anti-alias allows whole pixels
to either be inside or outside the clip. The fastest drawing has a aliased,
rectanglar clip.

If clipping Path has Anti-alias set, clip may partially clip a pixel, requiring
that drawing blend partially with the destination along the edge. A rotated 
rectangular anti-aliased clip looks smoother but draws slower.

Clip can combine with Rect and Round_Rect primitives; like
Path, these are transformed by Matrix before they are combined with Clip.

Clip can combine with Region. Region is assumed to be in Device coordinates
and is unaffected by Matrix.

#Example
#Height 90
    #Description
        Draw a red circle with an aliased clip and an anti-aliased clip.
        Use an image filter to zoom into the pixels drawn.
        The edge of the aliased clip fully draws pixels in the red circle.
        The edge of the anti-aliased clip partially draws pixels in the red circle.
    ##
    SkPaint redPaint, scalePaint;
    redPaint.setAntiAlias(true);
    redPaint.setColor(SK_ColorRED);
    canvas->save();
    for (bool antialias : { false, true } ) {
        canvas->save();
        canvas->clipRect(SkRect::MakeWH(19.5f, 11.5f), antialias);
        canvas->drawCircle(17, 11, 8, redPaint);
        canvas->restore();
        canvas->translate(16, 0);
    }
    canvas->restore();
    SkMatrix matrix;
    matrix.setScale(6, 6);
    scalePaint.setImageFilter(
            SkImageFilter::MakeMatrixFilter(matrix, kNone_SkFilterQuality, nullptr));
    SkCanvas::SaveLayerRec saveLayerRec(
            nullptr, &scalePaint, SkCanvas::kInitWithPrevious_SaveLayerFlag); 
    canvas->saveLayer(saveLayerRec);
    canvas->restore();
##

#Method void clipRect(const SkRect& rect, SkClipOp op, bool doAntiAlias)

Replace Clip with the intersection or difference of Clip and rect,
with an aliased or anti-aliased clip edge. rect is transformed by Matrix
before it is combined with Clip.

#Param  rect  Rectangle to combine with Clip ##
#Param  op    Clip_Op to apply to Clip ##
#Param  doAntiAlias  true if Clip is to be anti-aliased ##

#Example
#Height 128
void draw(SkCanvas* canvas) {
    canvas->rotate(10);
    SkPaint paint;
    paint.setAntiAlias(true);
    for (auto alias: { false, true } ) {
        canvas->save();
        canvas->clipRect(SkRect::MakeWH(90, 80), SkClipOp::kIntersect, alias);
        canvas->drawCircle(100, 60, 60, paint);
        canvas->restore();
        canvas->translate(80, 0);
    }
}
##

#ToDo incomplete ##

##

#Method void clipRect(const SkRect& rect, SkClipOp op) 

Replace Clip with the intersection or difference of Clip and rect.
Resulting Clip is aliased; pixels are fully contained by the clip.
rect is transformed by Matrix before it is combined with Clip.

#Param  rect  Rectangle to combine with Clip ##
#Param  op    Clip_Op to apply to Clip ##

#Example
#Height 192
#Width 280
void draw(SkCanvas* canvas) {
    SkPaint paint;
    for (SkClipOp op: { SkClipOp::kIntersect, SkClipOp::kDifference } ) {
        canvas->save();
        canvas->clipRect(SkRect::MakeWH(90, 120), op, false);
        canvas->drawCircle(100, 100, 60, paint);
        canvas->restore();
        canvas->translate(80, 0);
    }
}
##

#ToDo incomplete ##

##

#Method void clipRect(const SkRect& rect, bool doAntiAlias = false) 

Replace Clip with the intersection of Clip and rect.
Resulting Clip is aliased; pixels are fully contained by the clip.
rect is transformed by Matrix
before it is combined with Clip.

#Param  rect  Rectangle to combine with Clip ##
#Param  doAntiAlias  true if Clip is to be anti-aliased ##

#Example
#Height 133
    #Description
        A circle drawn in pieces looks uniform when drawn aliased.
        The same circle pieces blend with pixels more than once when anti-aliased,
        visible as a thin pair of lines through the right circle.
    ##
void draw(SkCanvas* canvas) {
    canvas->clear(SK_ColorWHITE);
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setColor(0x8055aaff);
    SkRect clipRect = { 0, 0, 87.4f, 87.4f };
    for (auto alias: { false, true } ) {
        canvas->save();
        canvas->clipRect(clipRect, SkClipOp::kIntersect, alias);
        canvas->drawCircle(67, 67, 60, paint);
        canvas->restore();
        canvas->save();
        canvas->clipRect(clipRect, SkClipOp::kDifference, alias);
        canvas->drawCircle(67, 67, 60, paint);
        canvas->restore();
        canvas->translate(120, 0);
    }
}
##

#ToDo incomplete ##

##

#Method void androidFramework_setDeviceClipRestriction(const SkIRect& rect)

Sets the max clip rectangle, which can be set by clipRect, clipRRect and
clipPath and intersect the current clip with the specified rect.
The max clip affects only future ops (it is not retroactive).
The clip restriction is not recorded in pictures.

Pass an empty rect to disable max clip. 

#Private
This is private API to be used only by Android framework.
##

#Param  rect   maximum allowed clip in device coordinates
#Param ##

##

#Method void clipRRect(const SkRRect& rrect, SkClipOp op, bool doAntiAlias)

Replace Clip with the intersection or difference of Clip and rrect,
with an aliased or anti-aliased clip edge.
rrect is transformed by Matrix
before it is combined with Clip.

#Param  rrect  Round_Rect to combine with Clip ##
#Param  op  Clip_Op to apply to Clip ##
#Param  doAntiAlias  true if Clip is to be antialiased ##

#Example
#Height 128
void draw(SkCanvas* canvas) {
    canvas->clear(SK_ColorWHITE);
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setColor(0x8055aaff);
    SkRRect oval;
    oval.setOval({10, 20, 90, 100});
    canvas->clipRRect(oval, SkClipOp::kIntersect, true);
    canvas->drawCircle(70, 100, 60, paint);
}
##

#ToDo incomplete ##

##

#Method void clipRRect(const SkRRect& rrect, SkClipOp op) 

Replace Clip with the intersection or difference of Clip and rrect.
Resulting Clip is aliased; pixels are fully contained by the clip.
rrect is transformed by Matrix before it is combined with Clip.

#Param  rrect  Round_Rect to combine with Clip ##
#Param  op  Clip_Op to apply to Clip ##

#Example
#Height 128
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setColor(0x8055aaff);
    auto oval = SkRRect::MakeOval({10, 20, 90, 100});
    canvas->clipRRect(oval, SkClipOp::kIntersect);
    canvas->drawCircle(70, 100, 60, paint);
}
##

#ToDo incomplete ##

##

#Method void clipRRect(const SkRRect& rrect, bool doAntiAlias = false) 

Replace Clip with the intersection of Clip and rrect,
with an aliased or anti-aliased clip edge.
rrect is transformed by Matrix before it is combined with Clip.

#Param  rrect  Round_Rect to combine with Clip ##
#Param  doAntiAlias  true if Clip is to be antialiased ##

#Example
#Height 128
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    auto oval = SkRRect::MakeRectXY({10, 20, 90, 100}, 9, 13);
    canvas->clipRRect(oval, true);
    canvas->drawCircle(70, 100, 60, paint);
}
##

#ToDo incomplete ##

##

#Method void clipPath(const SkPath& path, SkClipOp op, bool doAntiAlias)

Replace Clip with the intersection or difference of Clip and path,
with an aliased or anti-aliased clip edge. Path_Fill_Type determines if path
describes the area inside or outside its contours; and if Path_Contour overlaps
itself or another Path_Contour, whether the overlaps form part of the area.
path is transformed by Matrix before it is combined with Clip.

#Param  path  Path to combine with Clip ##
#Param  op  Clip_Op to apply to Clip ##
#Param  doAntiAlias  true if Clip is to be antialiased ##

#Example
#Description
Top figure uses SkPath::kInverseWinding_FillType and SkClipOp::kDifference;
area outside clip is subtracted from circle.

Bottom figure uses SkPath::kWinding_FillType and SkClipOp::kIntersect;
area inside clip is intersected with circle.
##
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    SkPath path;
    path.addRect({20, 30, 100, 110});
    path.setFillType(SkPath::kInverseWinding_FillType);
    canvas->save();
    canvas->clipPath(path, SkClipOp::kDifference, false);
    canvas->drawCircle(70, 100, 60, paint);
    canvas->restore();
    canvas->translate(100, 100);
    path.setFillType(SkPath::kWinding_FillType);
    canvas->clipPath(path, SkClipOp::kIntersect, false);
    canvas->drawCircle(70, 100, 60, paint);
}
##

#ToDo incomplete ##

##

#Method void clipPath(const SkPath& path, SkClipOp op) 

Replace Clip with the intersection or difference of Clip and path.
Resulting Clip is aliased; pixels are fully contained by the clip.
Path_Fill_Type determines if path
describes the area inside or outside its contours; and if Path_Contour overlaps
itself or another Path_Contour, whether the overlaps form part of the area.
path is transformed by Matrix
before it is combined with Clip.

#Param  path  Path to combine with Clip ##
#Param  op  Clip_Op to apply to Clip ##

#Example
#Description
Overlapping Rects form a clip. When clip's Path_Fill_Type is set to
SkPath::kWinding_FillType, the overlap is included. Set to 
SkPath::kEvenOdd_FillType, the overlap is excluded and forms a hole.
##
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    SkPath path;
    path.addRect({20, 15, 100, 95});
    path.addRect({50, 65, 130, 135});
    path.setFillType(SkPath::kWinding_FillType);
    canvas->save();
    canvas->clipPath(path, SkClipOp::kIntersect);
    canvas->drawCircle(70, 85, 60, paint);
    canvas->restore();
    canvas->translate(100, 100);
    path.setFillType(SkPath::kEvenOdd_FillType);
    canvas->clipPath(path, SkClipOp::kIntersect);
    canvas->drawCircle(70, 85, 60, paint);
}
##

#ToDo incomplete ##

##

#Method void clipPath(const SkPath& path, bool doAntiAlias = false) 

Replace Clip with the intersection of Clip and path.
Resulting Clip is aliased; pixels are fully contained by the clip.
Path_Fill_Type determines if path
describes the area inside or outside its contours; and if Path_Contour overlaps
itself or another Path_Contour, whether the overlaps form part of the area.
path is transformed by Matrix before it is combined with Clip.

#Param  path  Path to combine with Clip ##
#Param  doAntiAlias  true if Clip is to be antialiased ##

#Example
#Height 212
#Description
Clip loops over itself covering its center twice. When clip's Path_Fill_Type 
is set to SkPath::kWinding_FillType, the overlap is included. Set to 
SkPath::kEvenOdd_FillType, the overlap is excluded and forms a hole.
##
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    SkPath path;
    SkPoint poly[] = {{20, 20}, { 80, 20}, { 80,  80}, {40,  80},
                      {40, 40}, {100, 40}, {100, 100}, {20, 100}};
    path.addPoly(poly, SK_ARRAY_COUNT(poly), true);
    path.setFillType(SkPath::kWinding_FillType);
    canvas->save();
    canvas->clipPath(path, SkClipOp::kIntersect);
    canvas->drawCircle(50, 50, 45, paint);
    canvas->restore();
    canvas->translate(100, 100);
    path.setFillType(SkPath::kEvenOdd_FillType);
    canvas->clipPath(path, SkClipOp::kIntersect);
    canvas->drawCircle(50, 50, 45, paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void setAllowSimplifyClip(bool allow) 

#Experimental
Only used for testing.
##

Set to simplify clip stack using path ops.

##

# ------------------------------------------------------------------------------

#Method void clipRegion(const SkRegion& deviceRgn, SkClipOp op = SkClipOp::kIntersect)

Replace Clip with the intersection or difference of Clip and Region deviceRgn.
Resulting Clip is aliased; pixels are fully contained by the clip.
deviceRgn is unaffected by Matrix.

#Param  deviceRgn    Region to combine with Clip ##
#Param  op  Clip_Op to apply to Clip ##

#Example
#Description
    region is unaffected by canvas rotation; rect is affected by canvas rotation.
    Both clips are aliased; this is unnoticable on Region clip because it
    aligns to pixel boundaries.
##
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    SkIRect iRect = {30, 40, 120, 130 };
    SkRegion region(iRect);
    canvas->rotate(10);
    canvas->save();
    canvas->clipRegion(region, SkClipOp::kIntersect);
    canvas->drawCircle(50, 50, 45, paint);
    canvas->restore();
    canvas->translate(100, 100);
    canvas->clipRect(SkRect::Make(iRect), SkClipOp::kIntersect);
    canvas->drawCircle(50, 50, 45, paint);
}
##

#ToDo incomplete ##

##

#Method bool quickReject(const SkRect& rect) const

Return true if Rect rect, transformed by Matrix, can be quickly determined to be
outside of Clip. May return false even though rect is outside of Clip.

Use to check if an area to be drawn is clipped out, to skip subsequent draw calls.

#Param  rect  Rect to compare with Clip ##

#Return  true if rect, transformed by Matrix, does not intersect Clip ##

#Example
void draw(SkCanvas* canvas) {
    SkRect testRect = {30, 30, 120, 129 }; 
    SkRect clipRect = {30, 130, 120, 230 }; 
    canvas->save();
    canvas->clipRect(clipRect);
    SkDebugf("quickReject %s\n", canvas->quickReject(testRect) ? "true" : "false");
    canvas->restore();
    canvas->rotate(10);
    canvas->clipRect(clipRect);
    SkDebugf("quickReject %s\n", canvas->quickReject(testRect) ? "true" : "false");
}
    #StdOut
        quickReject true
        quickReject false
    ##
##

#ToDo incomplete ##

##

#Method bool quickReject(const SkPath& path) const

Return true if path, transformed by Matrix, can be quickly determined to be
outside of Clip. May return false even though path is outside of Clip.

Use to check if an area to be drawn is clipped out, to skip subsequent draw calls.

#Param path  Path to compare with Clip ##

#Return  true if path, transformed by Matrix, does not intersect Clip ##

#Example
void draw(SkCanvas* canvas) {
    SkPoint testPoints[] = {{30,  30}, {120,  30}, {120, 129} }; 
    SkPoint clipPoints[] = {{30, 130}, {120, 130}, {120, 230} }; 
    SkPath testPath, clipPath;
    testPath.addPoly(testPoints, SK_ARRAY_COUNT(testPoints), true);
    clipPath.addPoly(clipPoints, SK_ARRAY_COUNT(clipPoints), true);
    canvas->save();
    canvas->clipPath(clipPath);
    SkDebugf("quickReject %s\n", canvas->quickReject(testPath) ? "true" : "false");
    canvas->restore();
    canvas->rotate(10);
    canvas->clipPath(clipPath);
    SkDebugf("quickReject %s\n", canvas->quickReject(testPath) ? "true" : "false");
    #StdOut
        quickReject true
        quickReject false
    ##
}
##

#ToDo incomplete ##

##

#Method SkRect getLocalClipBounds() const 

Return bounds of Clip, transformed by inverse of Matrix. If Clip is empty,
return SkRect::MakeEmpty, where all Rect sides equal zero.

Rect returned is outset by one to account for partial pixel coverage if Clip
is anti-aliased.

#Return  bounds of Clip in local coordinates ##

#Example
    #Description 
        Initial bounds is device bounds outset by 1 on all sides.
        Clipped bounds is clipPath bounds outset by 1 on all sides.
        Scaling the canvas by two in x and y scales the local bounds by 1/2 in x and y.
    ##
    SkCanvas local(256, 256);
    canvas = &local;
    SkRect bounds = canvas->getLocalClipBounds();
    SkDebugf("left:%g  top:%g  right:%g  bottom:%g\n",
            bounds.fLeft, bounds.fTop, bounds.fRight, bounds.fBottom);
    SkPoint clipPoints[]  = {{30, 130}, {120, 130}, {120, 230} }; 
    SkPath clipPath;
    clipPath.addPoly(clipPoints, SK_ARRAY_COUNT(clipPoints), true);
    canvas->clipPath(clipPath);
    bounds = canvas->getLocalClipBounds();
    SkDebugf("left:%g  top:%g  right:%g  bottom:%g\n",
            bounds.fLeft, bounds.fTop, bounds.fRight, bounds.fBottom);
    canvas->scale(2, 2);
    bounds = canvas->getLocalClipBounds();
    SkDebugf("left:%g  top:%g  right:%g  bottom:%g\n",
            bounds.fLeft, bounds.fTop, bounds.fRight, bounds.fBottom);
    #StdOut
        left:-1  top:-1  right:257  bottom:257
        left:29  top:129  right:121  bottom:231
        left:14.5  top:64.5  right:60.5  bottom:115.5
    ##
##

# local canvas in example works around bug in fiddle ##
#Bug 6524  ##

##

#Method bool getLocalClipBounds(SkRect* bounds) const 

Return bounds of Clip, transformed by inverse of Matrix. If Clip is empty,
return false, and set bounds to SkRect::MakeEmpty, where all Rect sides equal zero.

bounds is outset by one to account for partial pixel coverage if Clip
is anti-aliased.

#Param bounds  Rect of Clip in local coordinates ##

#Return  true if Clip bounds is not empty ##

#Example
    void draw(SkCanvas* canvas) {
        SkCanvas local(256, 256);
        canvas = &local;
        SkRect bounds;
        SkDebugf("local bounds empty = %s\n", canvas->getLocalClipBounds(&bounds)
                 ? "false" : "true");
        SkPath path;
        canvas->clipPath(path);
        SkDebugf("local bounds empty = %s\n", canvas->getLocalClipBounds(&bounds)
                 ? "false" : "true");
    }
    #StdOut
        local bounds empty = false
        local bounds empty = true
    ##
##

# local canvas in example works around bug in fiddle ##
#Bug 6524  ##

##

#Method SkIRect getDeviceClipBounds() const 

Return IRect bounds of Clip, unaffected by Matrix. If Clip is empty,
return SkRect::MakeEmpty, where all Rect sides equal zero.

Unlike getLocalClipBounds, returned IRect is not outset. 

#Return  bounds of Clip in Device coordinates ##

#Example
void draw(SkCanvas* canvas) {
    #Description
        Initial bounds is device bounds, not outset.
        Clipped bounds is clipPath bounds, not outset.
        Scaling the canvas by 1/2 in x and y scales the device bounds by 1/2 in x and y.
    ##
    SkCanvas device(256, 256);
    canvas = &device;
    SkIRect bounds = canvas->getDeviceClipBounds();
    SkDebugf("left:%d  top:%d  right:%d  bottom:%d\n",
            bounds.fLeft, bounds.fTop, bounds.fRight, bounds.fBottom);
    SkPoint clipPoints[]  = {{30, 130}, {120, 130}, {120, 230} }; 
    SkPath clipPath;
    clipPath.addPoly(clipPoints, SK_ARRAY_COUNT(clipPoints), true);
    canvas->save();
    canvas->clipPath(clipPath);
    bounds = canvas->getDeviceClipBounds();
    SkDebugf("left:%d  top:%d  right:%d  bottom:%d\n",
            bounds.fLeft, bounds.fTop, bounds.fRight, bounds.fBottom);
    canvas->restore();
    canvas->scale(1.f/2, 1.f/2);
    canvas->clipPath(clipPath);
    bounds = canvas->getDeviceClipBounds();
    SkDebugf("left:%d  top:%d  right:%d  bottom:%d\n",
            bounds.fLeft, bounds.fTop, bounds.fRight, bounds.fBottom);
    #StdOut
        left:0  top:0  right:256  bottom:256
        left:30  top:130  right:120  bottom:230
        left:15  top:65  right:60  bottom:115
    ##
}
##

#ToDo some confusion on why with an identity Matrix local and device are different ##

# device canvas in example works around bug in fiddle ##
#Bug 6524  ##

##

#Method bool getDeviceClipBounds(SkIRect* bounds) const 

Return IRect bounds of Clip, unaffected by Matrix. If Clip is empty,
return false, and set bounds to SkRect::MakeEmpty, where all Rect sides equal zero.

Unlike getLocalClipBounds, bounds is not outset. 

#Param bounds  Rect of Clip in device coordinates ##

#Return  true if Clip bounds is not empty ##

#Example
    void draw(SkCanvas* canvas) {
        SkIRect bounds;
        SkDebugf("device bounds empty = %s\n", canvas->getDeviceClipBounds(&bounds)
                 ? "false" : "true");
        SkPath path;
        canvas->clipPath(path);
        SkDebugf("device bounds empty = %s\n", canvas->getDeviceClipBounds(&bounds)
                 ? "false" : "true");
    }
    #StdOut
        device bounds empty = false
        device bounds empty = true
    ##
##

#ToDo incomplete ##

##

#Topic Clip ##

# ------------------------------------------------------------------------------

#Method void drawColor(SkColor color, SkBlendMode mode = SkBlendMode::kSrcOver)

Fill Clip with Color color.
mode determines how Color_ARGB is combined with destination.

#Param color    Unpremultiplied Color_ARGB ##
#Param mode  SkBlendMode used to combine source color and destination ##

#Example
    canvas->drawColor(SK_ColorRED);
    canvas->clipRect(SkRect::MakeWH(150, 150));
    canvas->drawColor(SkColorSetARGB(0x80, 0x00, 0xFF, 0x00), SkBlendMode::kPlus);
    canvas->clipRect(SkRect::MakeWH(75, 75));
    canvas->drawColor(SkColorSetARGB(0x80, 0x00, 0x00, 0xFF), SkBlendMode::kPlus);
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void clear(SkColor color) 

Fill Clip with Color color using SkBlendMode::kSrc. 
This has the effect of replacing all pixels contained by Clip with color.

#Param color    Unpremultiplied Color_ARGB ##

#Example
void draw(SkCanvas* canvas) {
    canvas->save();
    canvas->clipRect(SkRect::MakeWH(256, 128));
    canvas->clear(SkColorSetARGB(0x80, 0xFF, 0x00, 0x00)); 
    canvas->restore();
    canvas->save();
    canvas->clipRect(SkRect::MakeWH(150, 192));
    canvas->clear(SkColorSetARGB(0x80, 0x00, 0xFF, 0x00));
    canvas->restore();
    canvas->clipRect(SkRect::MakeWH(75, 256));
    canvas->clear(SkColorSetARGB(0x80, 0x00, 0x00, 0xFF));
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void discard() 

Make Canvas contents undefined. Subsequent calls that read Canvas pixels,
such as drawing with SkBlendMode, return undefined results. discard() does
not change Clip or Matrix.

discard() may do nothing, depending on the implementation of Surface or Device
that created Canvas.

discard() allows optimized performance on subsequent draws by removing
cached data associated with Surface or Device.
It is not necessary to call discard() once done with Canvas;
any cached data is deleted when owning Surface or Device is deleted.

#ToDo example? not sure how to make this meaningful w/o more implementation detail ##

#NoExample 
##

##

# ------------------------------------------------------------------------------

#Method void drawPaint(const SkPaint& paint)

Fill Clip with Paint paint. Paint components Rasterizer, Mask_Filter, Shader,
Color_Filter, Image_Filter, and Blend_Mode affect drawing;
Path_Effect in paint is ignored.

# can Path_Effect in paint ever alter drawPaint?

#Param  paint    graphics state used to fill Canvas ##

#Example
void draw(SkCanvas* canvas) {
    SkColor     colors[] = { SK_ColorRED, SK_ColorGREEN, SK_ColorBLUE };
    SkScalar    pos[] = { 0, SK_Scalar1/2, SK_Scalar1 };
    SkPaint     paint;
    paint.setShader(SkGradientShader::MakeSweep(256, 256, colors, pos, SK_ARRAY_COUNT(colors)));
    canvas->drawPaint(paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Enum PointMode

#Code
    enum PointMode {
        kPoints_PointMode,
        kLines_PointMode,
        kPolygon_PointMode 
    };
##

Selects if an array of points are drawn as discrete points, as lines, or as
an open polygon.

#Const kPoints_PointMode 0
    Draw each point separately.
##

#Const kLines_PointMode 1
    Draw each pair of points as a line segment.
##

#Const kPolygon_PointMode 2
    Draw the array of points as a open polygon.
##

#Example
    #Description 
        The upper left corner shows three squares when drawn as points.
        The upper right corner shows one line; when drawn as lines, two points are required per line.
        The lower right corner shows two lines; when draw as polygon, no miter is drawn at the corner.
        The lower left corner shows two lines with a miter when path contains polygon.
    ##
void draw(SkCanvas* canvas) {
  SkPaint paint;
  paint.setStyle(SkPaint::kStroke_Style);
  paint.setStrokeWidth(10);
  SkPoint points[] = {{64, 32}, {96, 96}, {32, 96}};
  canvas->drawPoints(SkCanvas::kPoints_PointMode, 3, points, paint);
  canvas->translate(128, 0);
  canvas->drawPoints(SkCanvas::kLines_PointMode, 3, points, paint);
  canvas->translate(0, 128);
  canvas->drawPoints(SkCanvas::kPolygon_PointMode, 3, points, paint);
  SkPath path;
  path.addPoly(points, 3, false);
  canvas->translate(-128, 0);
  canvas->drawPath(path, paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawPoints(PointMode mode, size_t count, const SkPoint pts[], const SkPaint& paint)

Draw pts using Clip, Matrix and Paint paint.
count is the number of points; if count is less than one, has no effect.
mode may be one of: kPoints_PointMode, kLines_PointMode, or kPolygon_PointMode.

If mode is kPoints_PointMode, the shape of point drawn depends on paint
Paint_Stroke_Cap. If paint is set to SkPaint::kRound_Cap, each point draws a
circle of diameter Paint_Stroke_Width. If paint is set to SkPaint::kSquare_Cap
or SkPaint::kButt_Cap, each point draws a square of width and height
Paint_Stroke_Width.

If mode is kLines_PointMode, each pair of points draws a line segment.
One line is drawn for every two points; each point is used once. If count is odd,
the final point is ignored. 

If mode is kPolygon_PointMode, each adjacent pair of points draws a line segment.
count minus one lines are drawn; the first and last point are used once.

Each line segment respects paint Paint_Stroke_Cap and Paint_Stroke_Width.
Paint_Style is ignored, as if were set to SkPaint::kStroke_Style.

Always draws each element one at a time; is not affected by
Paint_Stroke_Join, and unlike drawPath, does not create a mask from all points
and lines before drawing. 

#Param  mode     Whether pts draws points or lines ##
#Param  count    The number of points in the array ##
#Param  pts      Array of points to draw ##
#Param  paint    Stroke, blend, color, and so on, used to draw ##

#Example
#Height 200
    #Description 
    #List
    # The first column draws points. ##
    # The second column draws points as lines. ##
    # The third column draws points as a polygon. ##
    # The fourth column draws points as a polygonal path. ##
    # The first row uses a round cap and round join. ##
    # The second row uses a square cap and a miter join. ##
    # The third row uses a butt cap and a bevel join. ##
    ##
    The transparent color makes multiple line draws visible;
    the path is drawn all at once.
    ##
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setStyle(SkPaint::kStroke_Style);
    paint.setStrokeWidth(10);
    paint.setColor(0x80349a45);
    const SkPoint points[] = {{32, 16}, {48, 48}, {16, 32}};
    const SkPaint::Join join[] = { SkPaint::kRound_Join, 
                                   SkPaint::kMiter_Join,
                                   SkPaint::kBevel_Join };
    int joinIndex = 0;
    SkPath path;
    path.addPoly(points, 3, false);
    for (const auto cap : { SkPaint::kRound_Cap, SkPaint::kSquare_Cap, SkPaint::kButt_Cap } ) {
        paint.setStrokeCap(cap);
        paint.setStrokeJoin(join[joinIndex++]);
        for (const auto mode : { SkCanvas::kPoints_PointMode,
                                 SkCanvas::kLines_PointMode,
                                 SkCanvas::kPolygon_PointMode } ) {
            canvas->drawPoints(mode, 3, points, paint);
            canvas->translate(64, 0);
        }
        canvas->drawPath(path, paint);
        canvas->translate(-192, 64);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawPoint(SkScalar x, SkScalar y, const SkPaint& paint)

Draw point at (x, y) using Clip, Matrix and Paint paint.

The shape of point drawn depends on paint Paint_Stroke_Cap.
If paint is set to SkPaint::kRound_Cap, draw a circle of diameter
Paint_Stroke_Width. If paint is set to SkPaint::kSquare_Cap or SkPaint::kButt_Cap, 
draw a square of width and height Paint_Stroke_Width.
Paint_Style is ignored, as if were set to SkPaint::kStroke_Style.

#Param  x        left edge of circle or square ##
#Param  y        top edge of circle or square ##
#Param  paint    stroke, blend, color, and so on, used to draw ##

#Example
void draw(SkCanvas* canvas) {
  SkPaint paint;
  paint.setAntiAlias(true);
  paint.setColor(0x80349a45);
  paint.setStyle(SkPaint::kStroke_Style);
  paint.setStrokeWidth(100);
  paint.setStrokeCap(SkPaint::kRound_Cap);
  canvas->scale(1, 1.2f);
  canvas->drawPoint(64, 96, paint);
  canvas->scale(.6f, .8f);
  paint.setColor(SK_ColorWHITE);
  canvas->drawPoint(106, 120, paint);
}
##

#ToDo incomplete ##

##

#Method void drawPoint(SkPoint p, const SkPaint& paint)

Draw point p using Clip, Matrix and Paint paint.

The shape of point drawn depends on paint Paint_Stroke_Cap.
If paint is set to SkPaint::kRound_Cap, draw a circle of diameter
Paint_Stroke_Width. If paint is set to SkPaint::kSquare_Cap or SkPaint::kButt_Cap, 
draw a square of width and height Paint_Stroke_Width.
Paint_Style is ignored, as if were set to SkPaint::kStroke_Style.

#Param  p        top-left edge of circle or square ##
#Param  paint    stroke, blend, color, and so on, used to draw ##

#Example
void draw(SkCanvas* canvas) {
  SkPaint paint;
  paint.setAntiAlias(true);
  paint.setColor(0x80349a45);
  paint.setStyle(SkPaint::kStroke_Style);
  paint.setStrokeWidth(100);
  paint.setStrokeCap(SkPaint::kSquare_Cap);
  canvas->scale(1, 1.2f);
  canvas->drawPoint({64, 96}, paint);
  canvas->scale(.6f, .8f);
  paint.setColor(SK_ColorWHITE);
  canvas->drawPoint(106, 120, paint);
}
##

#SeeAlso drawPoints drawCircle drawRect

##

# ------------------------------------------------------------------------------

#Method void drawLine(SkScalar x0, SkScalar y0, SkScalar x1, SkScalar y1, const SkPaint& paint)

Draws line segment from (x0, y0) to (x1, y1) using Clip, Matrix, and Paint paint.
In paint: Paint_Stroke_Width describes the line thickness;
Paint_Stroke_Cap draws the end rounded or square;
Paint_Style is ignored, as if were set to SkPaint::kStroke_Style.

#Param  x0    start of line segment on x-axis ##
#Param  y0    start of line segment on y-axis ##
#Param  x1    end of line segment on x-axis ##
#Param  y1    end of line segment on y-axis ##
#Param  paint stroke, blend, color, and so on, used to draw ##

#Example
  SkPaint paint;
  paint.setAntiAlias(true);
  paint.setColor(0xFF9a67be);
  paint.setStrokeWidth(20);
  canvas->skew(1, 0);
  canvas->drawLine(32, 96, 32, 160, paint);
  canvas->skew(-2, 0);
  canvas->drawLine(288, 96, 288, 160, paint);
##

#ToDo incomplete ##

##

#Method void drawLine(SkPoint p0, SkPoint p1, const SkPaint& paint)

Draws line segment from p0 to p1 using Clip, Matrix, and Paint paint.
In paint: Paint_Stroke_Width describes the line thickness;
Paint_Stroke_Cap draws the end rounded or square;
Paint_Style is ignored, as if were set to SkPaint::kStroke_Style.

#Param  p0    start of line segment ##
#Param  p1    end of line segment ##
#Param  paint  stroke, blend, color, and so on, used to draw ##

#Example
  SkPaint paint;
  paint.setAntiAlias(true);
  paint.setColor(0xFF9a67be);
  paint.setStrokeWidth(20);
  canvas->skew(1, 0);
  canvas->drawLine({32, 96}, {32, 160}, paint);
  canvas->skew(-2, 0);
  canvas->drawLine({288, 96}, {288, 160}, paint);
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawRect(const SkRect& rect, const SkPaint& paint)

Draw Rect rect using Clip, Matrix, and Paint paint.
In paint: Paint_Style determines if rectangle is stroked or filled; 
if stroked, Paint_Stroke_Width describes the line thickness, and
Paint_Stroke_Join draws the corners rounded or square.

#Param  rect     rectangle to be drawn ##
#Param  paint    stroke or fill, blend, color, and so on, used to draw ##

#Example
void draw(SkCanvas* canvas) {
    SkPoint rectPts[] = { {64, 48}, {192, 160} };
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setStyle(SkPaint::kStroke_Style);
    paint.setStrokeWidth(20);
    paint.setStrokeJoin(SkPaint::kRound_Join);
    SkMatrix rotator;
    rotator.setRotate(30, 128, 128);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, SK_ColorYELLOW, SK_ColorMAGENTA } ) {
        paint.setColor(color);
        SkRect rect;
        rect.set(rectPts[0], rectPts[1]);
        canvas->drawRect(rect, paint);
        rotator.mapPoints(rectPts, 2);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawIRect(const SkIRect& rect, const SkPaint& paint) 

Draw IRect rect using Clip, Matrix, and Paint paint.
In paint: Paint_Style determines if rectangle is stroked or filled; 
if stroked, Paint_Stroke_Width describes the line thickness, and
Paint_Stroke_Join draws the corners rounded or square.

#Param  rect     rectangle to be drawn ##
#Param  paint    stroke or fill, blend, color, and so on, used to draw ##

#Example
    SkIRect rect = { 64, 48, 192, 160 };
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setStyle(SkPaint::kStroke_Style);
    paint.setStrokeWidth(20);
    paint.setStrokeJoin(SkPaint::kRound_Join);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, SK_ColorYELLOW, SK_ColorMAGENTA } ) {
        paint.setColor(color);
        canvas->drawIRect(rect, paint);
        canvas->rotate(30, 128, 128);
    }
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawRegion(const SkRegion& region, const SkPaint& paint)

Draw Region region using Clip, Matrix, and Paint paint.
In paint: Paint_Style determines if rectangle is stroked or filled; 
if stroked, Paint_Stroke_Width describes the line thickness, and
Paint_Stroke_Join draws the corners rounded or square.

#Param  region   region to be drawn ##
#Param  paint    Paint stroke or fill, blend, color, and so on, used to draw ##

#Example
void draw(SkCanvas* canvas) {
    SkRegion region;
    region.op( 10, 10, 50, 50, SkRegion::kUnion_Op);
    region.op( 10, 50, 90, 90, SkRegion::kUnion_Op);
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setStyle(SkPaint::kStroke_Style);
    paint.setStrokeWidth(20);
    paint.setStrokeJoin(SkPaint::kRound_Join);
    canvas->drawRegion(region, paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawOval(const SkRect& oval, const SkPaint& paint)

Draw Oval oval using Clip, Matrix, and Paint.
In paint: Paint_Style determines if Oval is stroked or filled; 
if stroked, Paint_Stroke_Width describes the line thickness.

#Param  oval     Rect bounds of Oval ##
#Param  paint    Paint stroke or fill, blend, color, and so on, used to draw ##

#Example
void draw(SkCanvas* canvas) {
    canvas->clear(0xFF3f5f9f);
    SkColor  kColor1 = SkColorSetARGB(0xff, 0xff, 0x7f, 0);
    SkColor  g1Colors[] = { kColor1, SkColorSetA(kColor1, 0x20) };
    SkPoint  g1Points[] = { { 0, 0 }, { 0, 100 } };
    SkScalar pos[] = { 0.2f, 1.0f };
    SkRect bounds = SkRect::MakeWH(80, 70);
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setShader(SkGradientShader::MakeLinear(g1Points, g1Colors, pos, SK_ARRAY_COUNT(g1Colors),
            SkShader::kClamp_TileMode));
    canvas->drawOval(bounds , paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawRRect(const SkRRect& rrect, const SkPaint& paint)

Draw Round_Rect rrect using Clip, Matrix, and Paint paint.
In paint: Paint_Style determines if rrect is stroked or filled; 
if stroked, Paint_Stroke_Width describes the line thickness.

rrect may represent a rectangle, circle, oval, uniformly rounded rectangle, or
may have any combination of positive non-square radii for the four corners.

#Param  rrect    Round_Rect with up to eight corner radii to draw ##
#Param  paint    Paint stroke or fill, blend, color, and so on, used to draw ##

#Example
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    SkRect outer = {30, 40, 210, 220};
    SkRect radii = {30, 50, 70, 90 };
    SkRRect rRect;
    rRect.setNinePatch(outer, radii.fLeft, radii.fTop, radii.fRight, radii.fBottom);
    canvas->drawRRect(rRect, paint);
    paint.setColor(SK_ColorWHITE);
    canvas->drawLine(outer.fLeft + radii.fLeft, outer.fTop,
                     outer.fLeft + radii.fLeft, outer.fBottom, paint);
    canvas->drawLine(outer.fRight - radii.fRight, outer.fTop, 
                     outer.fRight - radii.fRight, outer.fBottom, paint);
    canvas->drawLine(outer.fLeft,  outer.fTop + radii.fTop, 
                     outer.fRight, outer.fTop + radii.fTop, paint);
    canvas->drawLine(outer.fLeft,  outer.fBottom - radii.fBottom, 
                     outer.fRight, outer.fBottom - radii.fBottom, paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawDRRect(const SkRRect& outer, const SkRRect& inner, const SkPaint& paint)

Draw Round_Rect outer and inner
using Clip, Matrix, and Paint paint. 
outer must contain inner or the drawing is undefined.
In paint: Paint_Style determines if rrect is stroked or filled; 
if stroked, Paint_Stroke_Width describes the line thickness.
If stroked and Round_Rect corner has zero length radii, Paint_Stroke_Join can
draw corners rounded or square. 

GPU-backed platforms optimize drawing when both outer and inner are
concave and outer contains inner. These platforms may not be able to draw
Path built with identical data as fast. 

#Param  outer    Round_Rect outer bounds to draw ##
#Param  inner    Round_Rect inner bounds to draw ##
#Param  paint    Paint stroke or fill, blend, color, and so on, used to draw ##

#Example
void draw(SkCanvas* canvas) {
   SkRRect outer = SkRRect::MakeRect({20, 40, 210, 200});
   SkRRect inner = SkRRect::MakeOval({60, 70, 170, 160});
   SkPaint paint;
   canvas->drawDRRect(outer, inner, paint);
}
##

#Example
#Description
    Outer Rect has no corner radii, but stroke join is rounded.
    Inner Round_Rect has corner radii; outset stroke increases radii of corners.
    Stroke join does not affect inner Round_Rect since it has no sharp corners.
##
void draw(SkCanvas* canvas) {
   SkRRect outer = SkRRect::MakeRect({20, 40, 210, 200});
   SkRRect inner = SkRRect::MakeRectXY({60, 70, 170, 160}, 10, 10);
   SkPaint paint;
   paint.setAntiAlias(true);
   paint.setStyle(SkPaint::kStroke_Style);
   paint.setStrokeWidth(20);
   paint.setStrokeJoin(SkPaint::kRound_Join);
   canvas->drawDRRect(outer, inner, paint);
   paint.setStrokeWidth(1);
   paint.setColor(SK_ColorWHITE);
   canvas->drawDRRect(outer, inner, paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawCircle(SkScalar cx, SkScalar cy, SkScalar radius, const SkPaint& paint)

Draw Circle at (cx, cy) with radius using Clip, Matrix, and Paint paint.
If radius is zero or less, nothing is drawn.
In paint: Paint_Style determines if Circle is stroked or filled; 
if stroked, Paint_Stroke_Width describes the line thickness.

#Param  cx       Circle center on the x-axis ##
#Param  cy       Circle center on the y-axis ##
#Param  radius   half the diameter of Circle ##
#Param  paint    Paint stroke or fill, blend, color, and so on, used to draw ##

#Example
    void draw(SkCanvas* canvas) {
        SkPaint paint;
        paint.setAntiAlias(true);
        canvas->drawCircle(128, 128, 90, paint);
        paint.setColor(SK_ColorWHITE);
        canvas->drawCircle(86, 86, 20, paint);
        canvas->drawCircle(160, 76, 20, paint);
        canvas->drawCircle(140, 150, 35, paint);
    }
##

#ToDo incomplete ##

##

#Method void drawCircle(SkPoint center, SkScalar radius, const SkPaint& paint)

Draw Circle at (cx, cy) with radius using Clip, Matrix, and Paint paint.
If radius is zero or less, nothing is drawn.
In paint: Paint_Style determines if Circle is stroked or filled; 
if stroked, Paint_Stroke_Width describes the line thickness.

#Param  center   Circle center ##
#Param  radius   half the diameter of Circle ##
#Param  paint    Paint stroke or fill, blend, color, and so on, used to draw ##

#Example
    void draw(SkCanvas* canvas) {
        SkPaint paint;
        paint.setAntiAlias(true);
        canvas->drawCircle(128, 128, 90, paint);
        paint.setColor(SK_ColorWHITE);
        canvas->drawCircle({86, 86}, 20, paint);
        canvas->drawCircle({160, 76}, 20, paint);
        canvas->drawCircle({140, 150}, 35, paint);
    }
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawArc(const SkRect& oval, SkScalar startAngle, SkScalar sweepAngle,
                 bool useCenter, const SkPaint& paint)

Draw Arc using Clip, Matrix, and Paint paint.

Arc is part of Oval bounded by oval, sweeping from startAngle to startAngle plus
sweepAngle. startAngle and sweepAngle are in degrees.

startAngle of zero places start point at the right middle edge of oval.
A positive sweepAngle places Arc end point clockwise from start point;
a negative sweepAngle places Arc end point counterclockwise from start point.
sweepAngle may exceed 360 degrees, a full circle.
If useCenter is true, draw a wedge that includes lines from oval
center to Arc end points. If useCenter is false, draw Arc between end points.

If Rect oval is empty or sweepAngle is zero, nothing is drawn.

#Param  oval     Rect bounds of Oval containing Arc to draw ##
#Param  startAngle angle in degrees where Arc begins ##
#Param  sweepAngle sweep angle in degrees; positive is clockwise ##
#Param  useCenter if true, include the center of the oval ##
#Param  paint    Paint stroke or fill, blend, color, and so on, used to draw ##

#Example
    void draw(SkCanvas* canvas) {
        SkPaint paint;
        paint.setAntiAlias(true);
        SkRect oval = { 4, 4, 60, 60};
        for (auto useCenter : { false, true } ) {
            for (auto style : { SkPaint::kFill_Style, SkPaint::kStroke_Style } ) {
                paint.setStyle(style);
                for (auto degrees : { 45, 90, 180, 360} ) {
                    canvas->drawArc(oval, 0, degrees , useCenter, paint);
                    canvas->translate(64, 0);
                }
                canvas->translate(-256, 64);
            }
        }
    }
##

#Example
#Height 64
    void draw(SkCanvas* canvas) {
        SkPaint paint;
        paint.setAntiAlias(true);
        paint.setStyle(SkPaint::kStroke_Style);
        paint.setStrokeWidth(4);
        SkRect oval = { 4, 4, 60, 60};
        float intervals[] = { 5, 5 };
        paint.setPathEffect(SkDashPathEffect::Make(intervals, 2, 2.5f));
        for (auto degrees : { 270, 360, 540, 720 } ) {
            canvas->drawArc(oval, 0, degrees, false, paint);
            canvas->translate(64, 0);
        }
    }
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawRoundRect(const SkRect& rect, SkScalar rx, SkScalar ry, const SkPaint& paint)

Draw Round_Rect bounded by Rect rect, with corner radii (rx, ry) using Clip,
Matrix, and Paint paint.

In paint: Paint_Style determines if Round_Rect is stroked or filled; 
if stroked, Paint_Stroke_Width describes the line thickness.
If rx or ry are less than zero, they are treated as if they are zero.
If rx plus ry exceeds rect width or rect height, radii are scaled down to fit.
If rx and ry are zero, Round_Rect is drawn as Rect and if stroked is affected by
Paint_Stroke_Join.

#Param  rect     Rect bounds of Round_Rect to draw ##
#Param  rx       semiaxis length in x of oval describing rounded corners ##
#Param  ry       semiaxis length in y of oval describing rounded corners ##
#Param  paint    stroke, blend, color, and so on, used to draw ##

#Example
#Description
    Top row has a zero radius a generates a rectangle.
    Second row radii sum to less than sides.
    Third row radii sum equals sides.
    Fourth row radii sum exceeds sides; radii are scaled to fit.
##
    void draw(SkCanvas* canvas) {
        SkVector radii[] = { {0, 20}, {10, 10}, {10, 20}, {10, 40} };
        SkPaint paint;
        paint.setStrokeWidth(15);
        paint.setStrokeJoin(SkPaint::kRound_Join);
        paint.setAntiAlias(true);
        for (auto style : { SkPaint::kStroke_Style, SkPaint::kFill_Style  } ) {
            paint.setStyle(style );
            for (size_t i = 0; i < SK_ARRAY_COUNT(radii); ++i) {
               canvas->drawRoundRect({10, 10, 60, 40}, radii[i].fX, radii[i].fY, paint);
               canvas->translate(0, 60);
            }
            canvas->translate(80, -240);
        }
    }
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawPath(const SkPath& path, const SkPaint& paint)

Draw Path path using Clip, Matrix, and Paint paint.
Path contains an array of Path_Contour, each of which may be open or closed.

In paint: Paint_Style determines if Round_Rect is stroked or filled:
if filled, Path_Fill_Type determines whether Path_Contour describes inside or
outside of fill; if stroked, Paint_Stroke_Width describes the line thickness,
Paint_Stroke_Cap describes line ends, and Paint_Stroke_Join describes how
corners are drawn.

#Param  path     Path to draw ##
#Param  paint    stroke, blend, color, and so on, used to draw ##

#Example
#Description
    Top rows draw stroked path with combinations of joins and caps. The open contour
    is affected by caps; the closed contour is affected by joins.
    Bottom row draws fill the same for open and closed contour. 
    First bottom column shows winding fills overlap.
    Second bottom column shows even odd fills exclude overlap.
    Third bottom column shows inverse winding fills area outside both contours.
##
void draw(SkCanvas* canvas) {
    SkPath path;
    path.moveTo(20, 20);
    path.quadTo(60, 20, 60, 60);
    path.close();
    path.moveTo(60, 20);
    path.quadTo(60, 60, 20, 60);
    SkPaint paint;
    paint.setStrokeWidth(10);
    paint.setAntiAlias(true);
    paint.setStyle(SkPaint::kStroke_Style);
    for (auto join: { SkPaint::kBevel_Join, SkPaint::kRound_Join, SkPaint::kMiter_Join } ) {
        paint.setStrokeJoin(join);
        for (auto cap: { SkPaint::kButt_Cap, SkPaint::kSquare_Cap, SkPaint::kRound_Cap  } ) {
            paint.setStrokeCap(cap);
            canvas->drawPath(path, paint);
            canvas->translate(80, 0);
        }
        canvas->translate(-240, 60);
    }
    paint.setStyle(SkPaint::kFill_Style);
    for (auto fill : { SkPath::kWinding_FillType, 
                       SkPath::kEvenOdd_FillType, 
                       SkPath::kInverseWinding_FillType } ) {
        path.setFillType(fill);
        canvas->save();
        canvas->clipRect({0, 10, 80, 70});
        canvas->drawPath(path, paint);
        canvas->restore();
        canvas->translate(80, 0);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------
#Topic Draw_Image

drawImage, drawImageRect, and drawImageNine can be called with a bare pointer or
a smart pointer as a convenience. The pairs of calls are otherwise identical.

#Method void drawImage(const SkImage* image, SkScalar left, SkScalar top, const SkPaint* paint = NULL)

Draw Image image, with its top-left corner at (left, top),
using Clip, Matrix, and optional Paint paint.

If paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter, Blend_Mode,
and Draw_Looper. If image is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from image bounds. If generated
mask extends beyond image bounds, replicate image edge colors, just as Shader
made from SkImage::makeShader with SkShader::kClamp_TileMode set replicates the
image's edge color when it samples outside of its bounds. 

#Param  image    uncompressed rectangular map of pixels ##
#Param  left     left side of image ##
#Param  top      top side of image ##
#Param  paint    Paint containing Blend_Mode, Color_Filter, Image_Filter,
                 and so on; or nullptr
##

#Example
#Height 64
#Image 4
void draw(SkCanvas* canvas) {
   // sk_sp<SkImage> image;
   SkImage* imagePtr = image.get();
   canvas->drawImage(imagePtr, 0, 0);
   SkPaint paint;
   canvas->drawImage(imagePtr, 80, 0, &paint);
   paint.setAlpha(0x80);
   canvas->drawImage(imagePtr, 160, 0, &paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawImage(const sk_sp<SkImage>& image, SkScalar left, SkScalar top,
                   const SkPaint* paint = NULL) 

Draw Image image, with its top-left corner at (left, top),
using Clip, Matrix, and optional Paint paint.

If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If image is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from image bounds. If generated
mask extends beyond image bounds, replicate image edge colors, just as Shader
made from SkImage::makeShader with SkShader::kClamp_TileMode set replicates the
image's edge color when it samples outside of its bounds. 

#Param  image    uncompressed rectangular map of pixels ##
#Param  left     left side of image ##
#Param  top      pop side of image ##
#Param  paint    Paint containing Blend_Mode, Color_Filter, Image_Filter,
                 and so on; or nullptr
##

#Example
#Height 64
#Image 4
void draw(SkCanvas* canvas) {
   // sk_sp<SkImage> image;
   canvas->drawImage(image, 0, 0);
   SkPaint paint;
   canvas->drawImage(image, 80, 0, &paint);
   paint.setAlpha(0x80);
   canvas->drawImage(image, 160, 0, &paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Enum SrcRectConstraint

#Code
    enum SrcRectConstraint {
        kStrict_SrcRectConstraint, 
        kFast_SrcRectConstraint, 
    };
##

SrcRectConstraint controls the behavior at the edge of the Rect src, provided to
drawImageRect, trading off speed for precision.

Image_Filter in Paint may sample multiple pixels in the image. Rect src
restricts the bounds of pixels that may be read. Image_Filter may slow down if
it cannot read outside the bounds, when sampling near the edge of Rect src. 
SrcRectConstraint specifies whether an Image_Filter is allowed to read pixels
outside Rect src.

#Const kStrict_SrcRectConstraint
    Requires Image_Filter to respect Rect src,
    sampling only inside of its bounds, possibly with a performance penalty.
##

#Const kFast_SrcRectConstraint
    Permits Image_Filter to sample outside of Rect src
    by half the width of Image_Filter, permitting it to run faster but with
    error at the image edges.
##

#Example
#Height 64
#Description
    redBorder contains a black and white checkerboard bordered by red.
    redBorder is drawn scaled by 16 on the left.
    The middle and right bitmaps are filtered checkboards.
    Drawing the checkerboard with kStrict_SrcRectConstraint shows only a blur of black and white.
    Drawing the checkerboard with kFast_SrcRectConstraint allows red to bleed in the corners.
##
void draw(SkCanvas* canvas) {
    SkBitmap redBorder;
    redBorder.allocPixels(SkImageInfo::MakeN32Premul(4, 4));
    SkCanvas checkRed(redBorder);
    checkRed.clear(SK_ColorRED);
    uint32_t checkers[][2] = { { SK_ColorBLACK, SK_ColorWHITE },
                               { SK_ColorWHITE, SK_ColorBLACK } };
    checkRed.writePixels(
            SkImageInfo::MakeN32Premul(2, 2), (void*) checkers, sizeof(checkers[0]), 1, 1);
    canvas->scale(16, 16);
    canvas->drawBitmap(redBorder, 0, 0, nullptr);
    canvas->resetMatrix();
    sk_sp<SkImage> image = SkImage::MakeFromBitmap(redBorder);
    SkPaint lowPaint;
    lowPaint.setFilterQuality(kLow_SkFilterQuality);
    for (auto constraint : { SkCanvas::kStrict_SrcRectConstraint,
                             SkCanvas::kFast_SrcRectConstraint } ) {
        canvas->translate(80, 0);
        canvas->drawImageRect(image.get(), SkRect::MakeLTRB(1, 1, 3, 3),
                SkRect::MakeLTRB(16, 16, 48, 48), &lowPaint, constraint);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawImageRect(const SkImage* image, const SkRect& src, const SkRect& dst,
                       const SkPaint* paint,
                       SrcRectConstraint constraint = kStrict_SrcRectConstraint)

Draw Rect src of Image image, scaled and translated to fill Rect dst.
Additionally transform draw using Clip, Matrix, and optional Paint paint.

If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If image is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from image bounds.

If generated mask extends beyond image bounds, replicate image edge colors, just
as Shader made from SkImage::makeShader with SkShader::kClamp_TileMode set
replicates the image's edge color when it samples outside of its bounds.

constraint set to kStrict_SrcRectConstraint limits Paint Filter_Quality to
sample within src; set to kFast_SrcRectConstraint allows sampling outside to
improve performance.

#Param  image      Image containing pixels, dimensions, and format ##
#Param  src        source Rect of image to draw from ##
#Param  dst        destination Rect of image to draw to ##
#Param  paint      Paint containing Blend_Mode, Color_Filter, Image_Filter,
                   and so on; or nullptr
##
#Param  constraint filter strictly within src or draw faster ##

#Example
#Height 64
#Description
    The left bitmap draws with Paint default kNone_SkFilterQuality, and stays within
    its bounds; there's no bleeding with kFast_SrcRectConstraint.
    the middle and right bitmaps draw with kLow_SkFilterQuality; with
    kStrict_SrcRectConstraint, the filter remains within the checkerboard, and
    with kFast_SrcRectConstraint red bleeds on the edges.
##
void draw(SkCanvas* canvas) {
    uint32_t pixels[][4] = { 
            { 0xFFFF0000, 0xFFFF0000, 0xFFFF0000, 0xFFFF0000 },
            { 0xFFFF0000, 0xFF000000, 0xFFFFFFFF, 0xFFFF0000 },
            { 0xFFFF0000, 0xFFFFFFFF, 0xFF000000, 0xFFFF0000 },
            { 0xFFFF0000, 0xFFFF0000, 0xFFFF0000, 0xFFFF0000 } };
    SkBitmap redBorder;
    redBorder.installPixels(SkImageInfo::MakeN32Premul(4, 4), 
            (void*) pixels, sizeof(pixels[0]));
    sk_sp<SkImage> image = SkImage::MakeFromBitmap(redBorder);
    SkPaint lowPaint;
    for (auto constraint : {
            SkCanvas::kFast_SrcRectConstraint,
            SkCanvas::kStrict_SrcRectConstraint,
            SkCanvas::kFast_SrcRectConstraint } ) {
        canvas->drawImageRect(image.get(), SkRect::MakeLTRB(1, 1, 3, 3),
                SkRect::MakeLTRB(16, 16, 48, 48), &lowPaint, constraint);
        lowPaint.setFilterQuality(kLow_SkFilterQuality);
        canvas->translate(80, 0);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawImageRect(const SkImage* image, const SkIRect& isrc, const SkRect& dst,
                       const SkPaint* paint, SrcRectConstraint constraint = kStrict_SrcRectConstraint)

Draw IRect isrc of Image image, scaled and translated to fill Rect dst.
Note that isrc is on integer pixel boundaries; dst may include fractional
boundaries. Additionally transform draw using Clip, Matrix, and optional Paint
paint. 

If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If image is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from image bounds.

If generated mask extends beyond image bounds, replicate image edge colors, just
as Shader made from SkImage::makeShader with SkShader::kClamp_TileMode set
replicates the image's edge color when it samples outside of its bounds.

constraint set to kStrict_SrcRectConstraint limits Paint Filter_Quality to
sample within src; set to kFast_SrcRectConstraint allows sampling outside to
improve performance.

#Param  image      Image containing pixels, dimensions, and format ##
#Param  isrc       source IRect of image to draw from ##
#Param  dst        destination Rect of image to draw to ##
#Param  paint      Paint containing Blend_Mode, Color_Filter, Image_Filter,
                   and so on; or nullptr
##
#Param  constraint filter strictly within src or draw faster ##

#Example
#Image 4
void draw(SkCanvas* canvas) {
    // sk_sp<SkImage> image;
    for (auto i : { 1, 2, 4, 8 } ) {
        canvas->drawImageRect(image.get(), SkIRect::MakeLTRB(0, 0, 100, 100), 
                SkRect::MakeXYWH(i * 20, i * 20, i * 20, i * 20), nullptr);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawImageRect(const SkImage* image, const SkRect& dst, const SkPaint* paint,
                       SrcRectConstraint constraint = kStrict_SrcRectConstraint)

Draw Image image, scaled and translated to fill Rect dst, using Clip, Matrix,
and optional Paint paint.

If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If image is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from image bounds.

If generated mask extends beyond image bounds, replicate image edge colors, just
as Shader made from SkImage::makeShader with SkShader::kClamp_TileMode set
replicates the image's edge color when it samples outside of its bounds.

constraint set to kStrict_SrcRectConstraint limits Paint Filter_Quality to
sample within src; set to kFast_SrcRectConstraint allows sampling outside to
improve performance.

#Param  image      Image containing pixels, dimensions, and format ##
#Param  dst        destination Rect of image to draw to ##
#Param  paint      Paint containing Blend_Mode, Color_Filter, Image_Filter,
                   and so on; or nullptr
##
#Param  constraint filter strictly within src or draw faster ##

#Example
#Image 4
void draw(SkCanvas* canvas) {
    // sk_sp<SkImage> image;
    for (auto i : { 20, 40, 80, 160 } ) {
        canvas->drawImageRect(image.get(), SkRect::MakeXYWH(i, i, i, i), nullptr);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawImageRect(const sk_sp<SkImage>& image, const SkRect& src, const SkRect& dst,
                       const SkPaint* paint,
                       SrcRectConstraint constraint = kStrict_SrcRectConstraint) 

Draw Rect src of Image image, scaled and translated to fill Rect dst.
Additionally transform draw using Clip, Matrix, and optional Paint paint.

If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If image is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from image bounds.

If generated mask extends beyond image bounds, replicate image edge colors, just
as Shader made from SkImage::makeShader with SkShader::kClamp_TileMode set
replicates the image's edge color when it samples outside of its bounds.

constraint set to kStrict_SrcRectConstraint limits Paint Filter_Quality to
sample within src; set to kFast_SrcRectConstraint allows sampling outside to
improve performance.

#Param  image      Image containing pixels, dimensions, and format ##
#Param  src        source Rect of image to draw from ##
#Param  dst        destination Rect of image to draw to ##
#Param  paint      Paint containing Blend_Mode, Color_Filter, Image_Filter,
                   and so on; or nullptr
##
#Param  constraint filter strictly within src or draw faster ##

#Example
#Height 64
#Description
    Canvas scales and translates; transformation from src to dst also scales.
    The two matrices are concatenated to create the final transformation.
##
void draw(SkCanvas* canvas) {
    uint32_t pixels[][2] = { { SK_ColorBLACK, SK_ColorWHITE },
                             { SK_ColorWHITE, SK_ColorBLACK } };
    SkBitmap bitmap;
    bitmap.installPixels(SkImageInfo::MakeN32Premul(2, 2), 
            (void*) pixels, sizeof(pixels[0]));
    sk_sp<SkImage> image = SkImage::MakeFromBitmap(bitmap);
    SkPaint paint;
    canvas->scale(4, 4);
    for (auto alpha : { 50, 100, 150, 255 } ) {
        paint.setAlpha(alpha);
        canvas->drawImageRect(image, SkRect::MakeWH(2, 2), SkRect::MakeWH(8, 8), &paint);
        canvas->translate(8, 0);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawImageRect(const sk_sp<SkImage>& image, const SkIRect& isrc, const SkRect& dst,
                       const SkPaint* paint, SrcRectConstraint constraint = kStrict_SrcRectConstraint) 

Draw IRect isrc of Image image, scaled and translated to fill Rect dst.
isrc is on integer pixel boundaries; dst may include fractional boundaries.
Additionally transform draw using Clip, Matrix, and optional Paint paint.

If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If image is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from image bounds.

If generated mask extends beyond image bounds, replicate image edge colors, just
as Shader made from SkImage::makeShader with SkShader::kClamp_TileMode set
replicates the image's edge color when it samples outside of its bounds.

constraint set to kStrict_SrcRectConstraint limits Paint Filter_Quality to
sample within src; set to kFast_SrcRectConstraint allows sampling outside to
improve performance.

#Param  image      Image containing pixels, dimensions, and format ##
#Param  isrc       source IRect of image to draw from ##
#Param  dst        destination Rect of image to draw to ##
#Param  paint      Paint containing Blend_Mode, Color_Filter, Image_Filter,
                   and so on; or nullptr
##
#Param  constraint filter strictly within src or draw faster ##

#Example
#Height 64
void draw(SkCanvas* canvas) {
    uint32_t pixels[][2] = { { 0x00000000, 0x55555555},
                             { 0xAAAAAAAA, 0xFFFFFFFF} };
    SkBitmap bitmap;
    bitmap.installPixels(SkImageInfo::MakeN32Premul(2, 2), 
            (void*) pixels, sizeof(pixels[0]));
    sk_sp<SkImage> image = SkImage::MakeFromBitmap(bitmap);
    SkPaint paint;
    canvas->scale(4, 4);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, SK_ColorGREEN } ) {
        paint.setColorFilter(SkColorFilter::MakeModeFilter(color, SkBlendMode::kPlus));
        canvas->drawImageRect(image, SkIRect::MakeWH(2, 2), SkRect::MakeWH(8, 8), &paint);
        canvas->translate(8, 0);
    }
}
##

#ToDo incomplete ##
##

# ------------------------------------------------------------------------------

#Method void drawImageRect(const sk_sp<SkImage>& image, const SkRect& dst, const SkPaint* paint,
                       SrcRectConstraint constraint = kStrict_SrcRectConstraint) 

Draw Image image, scaled and translated to fill Rect dst,
using Clip, Matrix, and optional Paint paint.

If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If image is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from image bounds.

If generated mask extends beyond image bounds, replicate image edge colors, just
as Shader made from SkImage::makeShader with SkShader::kClamp_TileMode set
replicates the image's edge color when it samples outside of its bounds.

constraint set to kStrict_SrcRectConstraint limits Paint Filter_Quality to
sample within src; set to kFast_SrcRectConstraint allows sampling outside to
improve performance.

#Param  image      Image containing pixels, dimensions, and format ##
#Param  dst        destination Rect of image to draw to ##
#Param  paint      Paint containing Blend_Mode, Color_Filter, Image_Filter,
                   and so on; or nullptr
##
#Param  constraint filter strictly within src or draw faster ##

#Example
#Height 64
void draw(SkCanvas* canvas) {
    uint32_t pixels[][2] = { { 0x00000000, 0x55550000},
                             { 0xAAAA0000, 0xFFFF0000} };
    SkBitmap bitmap;
    bitmap.installPixels(SkImageInfo::MakeN32Premul(2, 2), 
            (void*) pixels, sizeof(pixels[0]));
    sk_sp<SkImage> image = SkImage::MakeFromBitmap(bitmap);
    SkPaint paint;
    canvas->scale(4, 4);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, SK_ColorGREEN } ) {
        paint.setColorFilter(SkColorFilter::MakeModeFilter(color, SkBlendMode::kPlus));
        canvas->drawImageRect(image, SkRect::MakeWH(8, 8), &paint);
        canvas->translate(8, 0);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawImageNine(const SkImage* image, const SkIRect& center, const SkRect& dst,
                       const SkPaint* paint = nullptr)

Draw Image image stretched differentially to fit into Rect dst.
IRect center divides the image into nine sections: four sides, four corners, and
the center. Corners are unscaled or scaled down proportionately if their sides
are larger than dst; center and four sides are scaled to fit remaining space, if any.

Additionally transform draw using Clip, Matrix, and optional Paint paint.

If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If image is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from image bounds.

If generated mask extends beyond image bounds, replicate image edge colors, just
as Shader made from SkImage::makeShader with SkShader::kClamp_TileMode set
replicates the image's edge color when it samples outside of its bounds.

#Param  image      Image containing pixels, dimensions, and format ##
#Param  center     IRect edge of image corners and sides ##
#Param  dst        destination Rect of image to draw to ##
#Param  paint      Paint containing Blend_Mode, Color_Filter, Image_Filter,
                   and so on; or nullptr
##

#Example
#Height 128
#Description
    The leftmost image is smaller than center; only corners are drawn, all scaled to fit.
    The second image equals the size of center; only corners are drawn, unscaled.
    The remaining images are larger than center. All corners draw unscaled. The sides
    and center are scaled if needed to take up the remaining space.
##
void draw(SkCanvas* canvas) {
    SkIRect center = { 20, 10, 50, 40 };
    SkBitmap bitmap;
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(60, 60));
    SkCanvas bitCanvas(bitmap);
    SkPaint paint;
    SkColor gray = 0xFF000000;
    int left = 0;
    for (auto right: { center.fLeft, center.fRight, bitmap.width() } ) {
        int top = 0;
        for (auto bottom: { center.fTop, center.fBottom, bitmap.height() } ) {
            paint.setColor(gray);
            bitCanvas.drawIRect(SkIRect::MakeLTRB(left, top, right, bottom), paint);
            gray += 0x001f1f1f;
            top = bottom;
        }
        left = right; 
    }
    sk_sp<SkImage> image = SkImage::MakeFromBitmap(bitmap);
    SkImage* imagePtr = image.get();
    for (auto dest: { 20, 30, 40, 60, 90 } ) {
        canvas->drawImageNine(imagePtr, center, SkRect::MakeWH(dest, dest), nullptr);
        canvas->translate(dest + 4, 0);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawImageNine(const sk_sp<SkImage>& image, const SkIRect& center, const SkRect& dst,
                       const SkPaint* paint = nullptr) 

Draw Image image stretched differentially to fit into Rect dst.
IRect center divides the image into nine sections: four sides, four corners, and
the center. Corners are unscaled or scaled down proportionately if their sides
are larger than dst; center and four sides are scaled to fit remaining space, if any.

Additionally transform draw using Clip, Matrix, and optional Paint paint.

If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If image is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from image bounds.

If generated mask extends beyond image bounds, replicate image edge colors, just
as Shader made from SkImage::makeShader with SkShader::kClamp_TileMode set
replicates the image's edge color when it samples outside of its bounds.

#Param  image      Image containing pixels, dimensions, and format ##
#Param  center     IRect edge of image corners and sides ##
#Param  dst        destination Rect of image to draw to ##
#Param  paint      Paint containing Blend_Mode, Color_Filter, Image_Filter,
                   and so on; or nullptr
##

#Example
#Height 128
#Description
    The two leftmost images has four corners and sides to the left and right of center.
    The leftmost image scales the width of corners proportionately to fit.
    The third and fourth image corners are unscaled; the sides and center are scaled to 
    fill the remaining space.
    The rightmost image has four corners scaled vertically to fit, and uses sides above
    and below center to fill the remaining space.
##
void draw(SkCanvas* canvas) {
    SkIRect center = { 20, 10, 50, 40 };
    SkBitmap bitmap;
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(60, 60));
    SkCanvas bitCanvas(bitmap);
    SkPaint paint;
    SkColor gray = 0xFF000000;
    int left = 0;
    for (auto right: { center.fLeft, center.fRight, bitmap.width() } ) {
        int top = 0;
        for (auto bottom: { center.fTop, center.fBottom, bitmap.height() } ) {
            paint.setColor(gray);
            bitCanvas.drawIRect(SkIRect::MakeLTRB(left, top, right, bottom), paint);
            gray += 0x001f1f1f;
            top = bottom;
        }
        left = right; 
    }
    sk_sp<SkImage> image = SkImage::MakeFromBitmap(bitmap);
    for (auto dest: { 20, 30, 40, 60, 90 } ) {
        canvas->drawImageNine(image, center, SkRect::MakeWH(dest, 110 - dest), nullptr);
        canvas->translate(dest + 4, 0);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawBitmap(const SkBitmap& bitmap, SkScalar left, SkScalar top,
                    const SkPaint* paint = NULL)

Draw Bitmap bitmap, with its top-left corner at (left, top),
using Clip, Matrix, and optional Paint paint.

If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If bitmap is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from bitmap bounds.

If generated mask extends beyond bitmap bounds, replicate bitmap edge colors,
just as Shader made from SkShader::MakeBitmapShader with
SkShader::kClamp_TileMode set replicates the bitmap's edge color when it samples
outside of its bounds. 

#Param  bitmap   Bitmap containing pixels, dimensions, and format ##
#Param  left     left side of bitmap ##
#Param  top      top side of bitmap ##
#Param  paint    Paint containing Blend_Mode, Color_Filter, Image_Filter,
                 and so on; or nullptr
##

#Example
#Height 64
void draw(SkCanvas* canvas) {
    uint8_t pixels[][8] = { { 0x00, 0x00, 0x00, 0xFF, 0xFF, 0x00, 0x00, 0x00},
                            { 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00},
                            { 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00},
                            { 0xFF, 0xFF, 0x00, 0xFF, 0xFF, 0x00, 0xFF, 0xFF},
                            { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF},
                            { 0x00, 0x00, 0xFF, 0x00, 0x00, 0xFF, 0x00, 0x00},
                            { 0x00, 0xFF, 0x00, 0xFF, 0xFF, 0x00, 0xFF, 0x00},
                            { 0xFF, 0x00, 0xFF, 0x00, 0x00, 0xFF, 0x00, 0xFF} };
    SkBitmap bitmap;
    bitmap.installPixels(SkImageInfo::MakeA8(8, 8), 
            (void*) pixels, sizeof(pixels[0]));
    SkPaint paint;
    canvas->scale(4, 4);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, 0xFF007F00} ) {
        paint.setColor(color);
        canvas->drawBitmap(bitmap, 0, 0, &paint);
        canvas->translate(12, 0);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawBitmapRect(const SkBitmap& bitmap, const SkRect& src, const SkRect& dst,
                        const SkPaint* paint, SrcRectConstraint constraint = kStrict_SrcRectConstraint)

Draw Rect src of Bitmap bitmap, scaled and translated to fill Rect dst.
Additionally transform draw using Clip, Matrix, and optional Paint paint.

If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If bitmap is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from bitmap bounds.

If generated mask extends beyond bitmap bounds, replicate bitmap edge colors,
just as Shader made from SkShader::MakeBitmapShader with
SkShader::kClamp_TileMode set replicates the bitmap's edge color when it samples
outside of its bounds.

constraint set to kStrict_SrcRectConstraint limits Paint Filter_Quality to
sample within src; set to kFast_SrcRectConstraint allows sampling outside to
improve performance.

#Param  bitmap   Bitmap containing pixels, dimensions, and format ##
#Param  src      source Rect of image to draw from ##
#Param  dst      destination Rect of image to draw to ##
#Param  paint    Paint containing Blend_Mode, Color_Filter, Image_Filter,
                 and so on; or nullptr
##
#Param  constraint filter strictly within src or draw faster ##

#Example
#Height 64
void draw(SkCanvas* canvas) {
    uint8_t pixels[][8] = { { 0x00, 0x00, 0x00, 0xFF, 0xFF, 0x00, 0x00, 0x00},
                            { 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00},
                            { 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00},
                            { 0xFF, 0xFF, 0x00, 0xFF, 0xFF, 0x00, 0xFF, 0xFF},
                            { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF},
                            { 0x00, 0x00, 0xFF, 0x00, 0x00, 0xFF, 0x00, 0x00},
                            { 0x00, 0xFF, 0x00, 0x00, 0x00, 0x00, 0xFF, 0x00},
                            { 0x00, 0x00, 0xFF, 0x00, 0x00, 0xFF, 0x00, 0x00} };
    SkBitmap bitmap;
    bitmap.installPixels(SkImageInfo::MakeA8(8, 8), 
            (void*) pixels, sizeof(pixels[0]));
    SkPaint paint;
    paint.setMaskFilter(SkBlurMaskFilter::Make(kSolid_SkBlurStyle, 6));
    for (auto color : { SK_ColorRED, SK_ColorBLUE, 0xFF007F00} ) {
        paint.setColor(color);
        canvas->drawBitmapRect(bitmap, SkRect::MakeWH(8, 8), SkRect::MakeWH(32, 32), &paint);
        canvas->translate(48, 0);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawBitmapRect(const SkBitmap& bitmap, const SkIRect& isrc, const SkRect& dst,
                        const SkPaint* paint, SrcRectConstraint constraint = kStrict_SrcRectConstraint)

Draw IRect isrc of Bitmap bitmap, scaled and translated to fill Rect dst.
isrc is on integer pixel boundaries; dst may include fractional boundaries.
Additionally transform draw using Clip, Matrix, and optional Paint paint.

If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If bitmap is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from bitmap bounds.

If generated mask extends beyond bitmap bounds, replicate bitmap edge colors,
just as Shader made from SkShader::MakeBitmapShader with
SkShader::kClamp_TileMode set replicates the bitmap's edge color when it samples
outside of its bounds.

constraint set to kStrict_SrcRectConstraint limits Paint Filter_Quality to
sample within src; set to kFast_SrcRectConstraint allows sampling outside to
improve performance.

#Param  bitmap   Bitmap containing pixels, dimensions, and format ##
#Param  isrc     source IRect of image to draw from ##
#Param  dst      destination Rect of image to draw to ##
#Param  paint    Paint containing Blend_Mode, Color_Filter, Image_Filter,
                 and so on; or nullptr
##
#Param  constraint Filter strictly within src or draw faster ##

#Example
#Height 64
void draw(SkCanvas* canvas) {
    uint8_t pixels[][8] = { { 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00},
                            { 0x00, 0xFF, 0x00, 0x00, 0x00, 0x00, 0xFF, 0x00},
                            { 0xFF, 0x00, 0xFF, 0x00, 0xFF, 0x00, 0x00, 0xFF},
                            { 0xFF, 0x00, 0xFF, 0x00, 0xFF, 0x00, 0x00, 0xFF},
                            { 0xFF, 0x00, 0x00, 0x00, 0x00, 0xFF, 0x00, 0xFF},
                            { 0xFF, 0x00, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0xFF},
                            { 0x00, 0xFF, 0x00, 0x00, 0x00, 0x00, 0xFF, 0x00},
                            { 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00} };
    SkBitmap bitmap;
    bitmap.installPixels(SkImageInfo::MakeA8(8, 8), 
            (void*) pixels, sizeof(pixels[0]));
    SkPaint paint;
    paint.setFilterQuality(kHigh_SkFilterQuality);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, 0xFF007F00, 0xFF7f007f} ) {
        paint.setColor(color);
        canvas->drawBitmapRect(bitmap, SkIRect::MakeWH(8, 8), SkRect::MakeWH(32, 32), &paint);
        canvas->translate(48.25f, 0);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawBitmapRect(const SkBitmap& bitmap, const SkRect& dst, const SkPaint* paint,
                        SrcRectConstraint constraint = kStrict_SrcRectConstraint)

Draw Bitmap bitmap, scaled and translated to fill Rect dst.
isrc is on integer pixel boundaries; dst may include fractional boundaries.
Additionally transform draw using Clip, Matrix, and optional Paint paint.

If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If bitmap is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from bitmap bounds.

If generated mask extends beyond bitmap bounds, replicate bitmap edge colors,
just as Shader made from SkShader::MakeBitmapShader with
SkShader::kClamp_TileMode set replicates the bitmap's edge color when it samples
outside of its bounds.

constraint set to kStrict_SrcRectConstraint limits Paint Filter_Quality to
sample within src; set to kFast_SrcRectConstraint allows sampling outside to
improve performance.

#Param  bitmap   Bitmap containing pixels, dimensions, and format ##
#Param  dst      destination Rect of image to draw to ##
#Param  paint    Paint containing Blend_Mode, Color_Filter, Image_Filter,
                 and so on; or nullptr
##
#Param  constraint filter strictly within src or draw faster ##

#Example
#Height 64
void draw(SkCanvas* canvas) {
    uint32_t pixels[][2] = { { 0x00000000, 0x55550000},
                             { 0xAAAA0000, 0xFFFF0000} };
    SkBitmap bitmap;
    bitmap.installPixels(SkImageInfo::MakeN32Premul(2, 2), 
            (void*) pixels, sizeof(pixels[0]));
    SkPaint paint;
    canvas->scale(4, 4);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, SK_ColorGREEN } ) {
        paint.setColorFilter(SkColorFilter::MakeModeFilter(color, SkBlendMode::kPlus));
        canvas->drawBitmapRect(bitmap, SkRect::MakeWH(8, 8), &paint);
        canvas->translate(8, 0);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawBitmapNine(const SkBitmap& bitmap, const SkIRect& center, const SkRect& dst,
                        const SkPaint* paint = NULL)

Draw Bitmap bitmap stretched differentially to fit into Rect dst.
IRect center divides the bitmap into nine sections: four sides, four corners,
and the center. Corners are unscaled or scaled down proportionately if their
sides are larger than dst; center and four sides are scaled to fit remaining
space, if any.

Additionally transform draw using Clip, Matrix, and optional Paint paint.

If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If bitmap is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from bitmap bounds.

If generated mask extends beyond bitmap bounds, replicate bitmap edge colors,
just as Shader made from SkShader::MakeBitmapShader with
SkShader::kClamp_TileMode set replicates the bitmap's edge color when it samples
outside of its bounds.

#Param  bitmap     Bitmap containing pixels, dimensions, and format ##
#Param  center     IRect edge of image corners and sides ##
#Param  dst        destination Rect of image to draw to ##
#Param  paint    Paint containing Blend_Mode, Color_Filter, Image_Filter,
                 and so on; or nullptr
##

#Example
#Height 128
#Description
    The two leftmost bitmap draws has four corners and sides to the left and right of center.
    The leftmost bitmap draw scales the width of corners proportionately to fit.
    The third and fourth draw corners are unscaled; the sides and center are scaled to 
    fill the remaining space.
    The rightmost bitmap draw has four corners scaled vertically to fit, and uses sides above
    and below center to fill the remaining space.
##
void draw(SkCanvas* canvas) {
    SkIRect center = { 20, 10, 50, 40 };
    SkBitmap bitmap;
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(60, 60));
    SkCanvas bitCanvas(bitmap);
    SkPaint paint;
    SkColor gray = 0xFF000000;
    int left = 0;
    for (auto right: { center.fLeft, center.fRight, bitmap.width() } ) {
        int top = 0;
        for (auto bottom: { center.fTop, center.fBottom, bitmap.height() } ) {
            paint.setColor(gray);
            bitCanvas.drawIRect(SkIRect::MakeLTRB(left, top, right, bottom), paint);
            gray += 0x001f1f1f;
            top = bottom;
        }
        left = right; 
    }
    for (auto dest: { 20, 30, 40, 60, 90 } ) {
        canvas->drawBitmapNine(bitmap, center, SkRect::MakeWH(dest, 110 - dest), nullptr);
        canvas->translate(dest + 4, 0);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------
#Struct Lattice

    Lattice divides Bitmap or Image into a rectangular grid.
    Grid entries on even columns and even rows are fixed; these entries are
    always drawn at their original size if the destination is large enough.
    If the destination side is too small to hold the fixed entries, all fixed
    entries are proportionately scaled down to fit.
    The grid entries not on even columns and rows are scaled to fit the
    remaining space, if any.

#Code
    struct Lattice {
        enum Flags {...

        const int*     fXDivs;
        const int*     fYDivs;
        const Flags*   fFlags;
        int            fXCount;
        int            fYCount;
        const SkIRect* fBounds;
    };
##

    #Enum Flags
        #Code
            enum Flags : uint8_t {
                kTransparent_Flags = 1 << 0,
            };
        ##

        Optional setting per rectangular grid entry to make it transparent.

        #Const kTransparent_Flags 1
            Set to skip lattice rectangle by making it transparent.
        ##
    ##

    #Member const int*   fXDivs
        Array of x-coordinates that divide the bitmap vertically.
        Array entries must be unique, increasing, greater than or equal to
        fBounds left edge, and less than fBounds right edge.
        Set the first element to fBounds left to collapse the left column of
        fixed grid entries.
    ##

    #Member const int*   fYDivs
        Array of y-coordinates that divide the bitmap horizontally.
        Array entries must be unique, increasing, greater than or equal to
        fBounds top edge, and less than fBounds bottom edge.
        Set the first element to fBounds top to collapse the top row of fixed
        grid entries.
    ##

    #Member const Flags*  fFlags
        Optional array of Flags, one per rectangular grid entry:
        array length must be
    #Formula
        (fXCount + 1) * (fYCount + 1)
    ##
        .
        Array entries correspond to the rectangular grid entries, ascending
        left to right and then top to bottom.
    ##

    #Member int   fXCount
        Number of entries in fXDivs array; one less than the number of
        horizontal divisions.
    ##

    #Member int   fYCount
        Number of entries in fYDivs array; one less than the number of vertical
        divisions.
    ##

    #Member const SkIRect*   fBounds
       Optional subset IRect source to draw from.
       If nullptr, source bounds is dimensions of Bitmap or Image.
    ##

#Struct Lattice ##

#Method void drawBitmapLattice(const SkBitmap& bitmap, const Lattice& lattice, const SkRect& dst,
                           const SkPaint* paint = nullptr)

Draw Bitmap bitmap stretched differentially to fit into Rect dst.

Lattice lattice divides bitmap into a rectangular grid.
Each intersection of an even-numbered row and column is fixed; like the corners
of drawBitmapNine, fixed lattice elements never scale larger than their initial
size and shrink proportionately when all fixed elements exceed the bitmap's
dimension. All other grid elements scale to fill the available space, if any.

Additionally transform draw using Clip, Matrix, and optional Paint paint.

If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If bitmap is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from bitmap bounds.

If generated mask extends beyond bitmap bounds, replicate bitmap edge colors,
just as Shader made from SkShader::MakeBitmapShader with
SkShader::kClamp_TileMode set replicates the bitmap's edge color when it samples
outside of its bounds.

#Param  bitmap     Bitmap containing pixels, dimensions, and format ##
#Param  lattice    division of bitmap into fixed and variable rectangles ##
#Param  dst        destination Rect of image to draw to ##
#Param  paint    Paint containing Blend_Mode, Color_Filter, Image_Filter,
                 and so on; or nullptr
##

#Example
#Height 128
#Description
    The two leftmost bitmap draws has four corners and sides to the left and right of center.
    The leftmost bitmap draw scales the width of corners proportionately to fit.
    The third and fourth draw corners are unscaled; the sides are scaled to 
    fill the remaining space; the center is transparent.
    The rightmost bitmap draw has four corners scaled vertically to fit, and uses sides above
    and below center to fill the remaining space.
##
void draw(SkCanvas* canvas) {
    SkIRect center = { 20, 10, 50, 40 };
    SkBitmap bitmap;
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(60, 60));
    SkCanvas bitCanvas(bitmap);
    SkPaint paint;
    SkColor gray = 0xFF000000;
    int left = 0;
    for (auto right: { center.fLeft, center.fRight, bitmap.width() } ) {
        int top = 0;
        for (auto bottom: { center.fTop, center.fBottom, bitmap.height() } ) {
            paint.setColor(gray);
            bitCanvas.drawIRect(SkIRect::MakeLTRB(left, top, right, bottom), paint);
            gray += 0x001f1f1f;
            top = bottom;
        }
        left = right; 
    }
    const int xDivs[] = { center.fLeft, center.fRight };
    const int yDivs[] = { center.fTop, center.fBottom };
    SkCanvas::Lattice::Flags flags[3][3];
    memset(flags, 0, sizeof(flags));  
    flags[1][1] = SkCanvas::Lattice::kTransparent_Flags;
    SkCanvas::Lattice lattice = { xDivs, yDivs, flags[0], SK_ARRAY_COUNT(xDivs),
         SK_ARRAY_COUNT(yDivs), nullptr };
    for (auto dest: { 20, 30, 40, 60, 90 } ) {
        canvas->drawBitmapLattice(bitmap, lattice , SkRect::MakeWH(dest, 110 - dest), nullptr);
        canvas->translate(dest + 4, 0);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawImageLattice(const SkImage* image, const Lattice& lattice, const SkRect& dst,
                          const SkPaint* paint = nullptr)

Draw Image image stretched differentially to fit into Rect dst.

Lattice lattice divides image into a rectangular grid.
Each intersection of an even-numbered row and column is fixed; like the corners
of drawBitmapNine, fixed lattice elements never scale larger than their initial
size and shrink proportionately when all fixed elements exceed the bitmap's
dimension. All other grid elements scale to fill the available space, if any.

Additionally transform draw using Clip, Matrix, and optional Paint paint.

If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If bitmap is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from bitmap bounds.

If generated mask extends beyond bitmap bounds, replicate bitmap edge colors,
just as Shader made from SkShader::MakeBitmapShader with
SkShader::kClamp_TileMode set replicates the bitmap's edge color when it samples
outside of its bounds.

#Param  image      Image containing pixels, dimensions, and format ##
#Param  lattice    division of bitmap into fixed and variable rectangles ##
#Param  dst        destination Rect of image to draw to ##
#Param  paint    Paint containing Blend_Mode, Color_Filter, Image_Filter,
                 and so on; or nullptr
##

#Example
#Height 128
#Description
    The leftmost image is smaller than center; only corners are drawn, all scaled to fit.
    The second image equals the size of center; only corners are drawn, unscaled.
    The remaining images are larger than center. All corners draw unscaled. The sides
    are scaled if needed to take up the remaining space; the center is transparent.
##
void draw(SkCanvas* canvas) {
    SkIRect center = { 20, 10, 50, 40 };
    SkBitmap bitmap;
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(60, 60));
    SkCanvas bitCanvas(bitmap);
    SkPaint paint;
    SkColor gray = 0xFF000000;
    int left = 0;
    for (auto right: { center.fLeft, center.fRight, bitmap.width() } ) {
        int top = 0;
        for (auto bottom: { center.fTop, center.fBottom, bitmap.height() } ) {
            paint.setColor(gray);
            bitCanvas.drawIRect(SkIRect::MakeLTRB(left, top, right, bottom), paint);
            gray += 0x001f1f1f;
            top = bottom;
        }
        left = right; 
    }
    const int xDivs[] = { center.fLeft, center.fRight };
    const int yDivs[] = { center.fTop, center.fBottom };
    SkCanvas::Lattice::Flags flags[3][3];
    memset(flags, 0, sizeof(flags));  
    flags[1][1] = SkCanvas::Lattice::kTransparent_Flags;
    SkCanvas::Lattice lattice = { xDivs, yDivs, flags[0], SK_ARRAY_COUNT(xDivs),
         SK_ARRAY_COUNT(yDivs), nullptr };
    sk_sp<SkImage> image = SkImage::MakeFromBitmap(bitmap);
    SkImage* imagePtr = image.get();
    for (auto dest: { 20, 30, 40, 60, 90 } ) {
        canvas->drawImageNine(imagePtr, center, SkRect::MakeWH(dest, dest), nullptr);
        canvas->translate(dest + 4, 0);
    }
}
##

#ToDo incomplete ##

##

#Topic Draw_Image ##

# ------------------------------------------------------------------------------

#Method void drawText(const void* text, size_t byteLength, SkScalar x, SkScalar y,
                  const SkPaint& paint)

Draw text, with origin at (x, y), using Clip, Matrix, and Paint paint.

text's meaning depends on Paint_Text_Encoding; by default, text encoding is
UTF-8.

x and y meaning depends on Paint_Text_Align and Paint_Vertical_Text; by default
text draws left to right, positioning the first glyph's left side bearing at x
and its baseline at y. Text size is affected by Matrix and Paint_Text_Size. 

All elements of paint: Path_Effect, Rasterizer, Mask_Filter, Shader,
Color_Filter, Image_Filter, and Draw_Looper; apply to text. By default, draws
filled 12 point black glyphs.

#Param  text     character code points or glyphs drawn ##
#Param  byteLength   byte length of text array ##
#Param  x        start of text on x-axis ##
#Param  y        start of text on y-axis ##
#Param  paint    text size, blend, color, and so on, used to draw ##

#Example
#Height 200
#Description
    The same text is drawn varying Paint_Text_Size and varying
    Matrix. 
##
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    float textSizes[] = { 12, 18, 24, 36 };
    for (auto size: textSizes ) {
        paint.setTextSize(size);
        canvas->drawText("Aa", 2, 10, 20, paint);
        canvas->translate(0, size * 2);
    }
    paint.reset();
    paint.setAntiAlias(true);
    float yPos = 20;
    for (auto size: textSizes ) {
        float scale = size / 12.f;
        canvas->resetMatrix();
        canvas->translate(100, 0);
        canvas->scale(scale, scale);
        canvas->drawText("Aa", 2, 10 / scale, yPos / scale, paint);
        yPos += size * 2; 
    }
}
##

#ToDo incomplete ##

##

#Method void drawString(const char* string, SkScalar x, SkScalar y, const SkPaint& paint)

Draw null terminated string, with origin at (x, y), using Clip, Matrix, and
Paint paint.

string's meaning depends on Paint_Text_Encoding; by default, string encoding is
UTF-8. Other values of Paint_Text_Encoding are unlikely to produce the desired
results, since zero bytes may be embedded in the string.

x and y meaning depends on Paint_Text_Align and Paint_Vertical_Text; by default
string draws left to right, positioning the first glyph's left side bearing at x
and its baseline at y. Text size is affected by Matrix and Paint_Text_Size. 

All elements of paint: Path_Effect, Rasterizer, Mask_Filter, Shader,
Color_Filter, Image_Filter, and Draw_Looper; apply to text. By default, draws
filled 12 point black glyphs.

#Param  string   character code points or glyphs drawn,
                 ending with a char value of zero
##
#Param  x        start of string on x-axis ##
#Param  y        start of string on y-axis ##
#Param  paint    text size, blend, color, and so on, used to draw ##

#Example
   SkPaint paint;
   canvas->drawString("a small hello", 20, 20, paint);
##

#SeeAlso drawText

##

#Method void drawString(const SkString& string, SkScalar x, SkScalar y, const SkPaint& paint)

Draw null terminated string, with origin at (x, y), using Clip, Matrix, and
Paint paint.

string's meaning depends on Paint_Text_Encoding; by default, string encoding is
UTF-8. Other values of Paint_Text_Encoding are unlikely to produce the desired
results, since zero bytes may be embedded in the string.

x and y meaning depends on Paint_Text_Align and Paint_Vertical_Text; by default
string draws left to right, positioning the first glyph's left side bearing at x
and its baseline at y. Text size is affected by Matrix and Paint_Text_Size. 

All elements of paint: Path_Effect, Rasterizer, Mask_Filter, Shader,
Color_Filter, Image_Filter, and Draw_Looper; apply to text. By default, draws
filled 12 point black glyphs.

#Param  string   character code points or glyphs drawn,
                 ending with a char value of zero
##
#Param  x        start of string on x-axis ##
#Param  y        start of string on y-axis ##
#Param  paint    text size, blend, color, and so on, used to draw ##

#Example
   SkPaint paint;
   SkString string("a small hello");
   canvas->drawString(string, 20, 20, paint);
##

#SeeAlso drawText

##

# ------------------------------------------------------------------------------

#Method void drawPosText(const void* text, size_t byteLength, const SkPoint pos[],
                     const SkPaint& paint)

Draw each glyph in text with the origin in pos array, using Clip, Matrix, and
Paint paint. The number of entries in pos array must match the number of glyphs
described by byteLength of text.

text's meaning depends on Paint_Text_Encoding; by default, text encoding is
UTF-8. pos elements' meaning depends on Paint_Text_Align and Paint_Vertical_Text;
by default each glyph's left side bearing is positioned at x and its
baseline is positioned at y. Text size is affected by Matrix and
Paint_Text_Size. 

All elements of paint: Path_Effect, Rasterizer, Mask_Filter, Shader,
Color_Filter, Image_Filter, and Draw_Looper; apply to text. By default, draws
filled 12 point black glyphs.

Layout engines such as Harfbuzz typically position each glyph
rather than using the font's advance widths.

#Param  text     character code points or glyphs drawn ##
#Param  byteLength   byte length of text array ##
#Param  pos      array of glyph origins ##
#Param  paint    text size, blend, color, and so on, used to draw ##

#Example
#Height 120
void draw(SkCanvas* canvas) {
  const char hello[] = "HeLLo!";
  const SkPoint pos[] = { {40, 100}, {82, 95}, {115, 110}, {130, 95}, {145, 85},
    {172, 100} };
  SkPaint paint;
  paint.setTextSize(60);
  canvas->drawPosText(hello, strlen(hello), pos, paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawPosTextH(const void* text, size_t byteLength, const SkScalar xpos[], SkScalar constY,
                      const SkPaint& paint)

Draw each glyph in text with its (x, y) origin composed from xpos array and
constY, using Clip, Matrix, and Paint paint. The number of entries in xpos array
must match the number of glyphs described by byteLength of text.

text's meaning depends on Paint_Text_Encoding; by default, text encoding is
UTF-8. pos elements' meaning depends on Paint_Text_Align and Paint_Vertical_Text;
by default each glyph's left side bearing is positioned at an xpos element and
its baseline is positioned at constY. Text size is affected by Matrix and
Paint_Text_Size. 

All elements of paint: Path_Effect, Rasterizer, Mask_Filter, Shader,
Color_Filter, Image_Filter, and Draw_Looper; apply to text. By default, draws
filled 12 point black glyphs.

Layout engines such as Harfbuzz typically position each glyph
rather than using the font's advance widths if all glyphs share the same
baseline.

#Param  text     character code points or glyphs drawn ##
#Param  byteLength   byte length of text array ##
#Param  xpos     array of x positions, used to position each glyph ##
#Param  constY   shared y coordinate for all of x positions ##
#Param  paint    text size, blend, color, and so on, used to draw ##

#Example
#Height 40
    void draw(SkCanvas* canvas) {
        SkScalar xpos[] = { 20, 40, 80, 160 };
        SkPaint paint;
        canvas->drawPosTextH("XXXX", 4, xpos, 20, paint);
    }
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawTextOnPathHV(const void* text, size_t byteLength, const SkPath& path, SkScalar hOffset,
                          SkScalar vOffset, const SkPaint& paint)

Draw text on Path path, using Clip, Matrix, and Paint paint.

Origin of text is at distance hOffset along the path, offset by a perpendicular
vector of length vOffset. If the path section corresponding the glyph advance is
curved, the glyph is drawn curved to match; control points in the glyph are
mapped to projected points parallel to the path. If the text's advance is larger
than the path length, the excess text is clipped.

text's meaning depends on Paint_Text_Encoding; by default, text encoding is
UTF-8. Origin meaning depends on Paint_Text_Align and Paint_Vertical_Text; by
default text positions the first glyph's left side bearing at origin x and its
baseline at origin y. Text size is affected by Matrix and Paint_Text_Size. 

All elements of paint: Path_Effect, Rasterizer, Mask_Filter, Shader,
Color_Filter, Image_Filter, and Draw_Looper; apply to text. By default, draws
filled 12 point black glyphs.

#Param  text         character code points or glyphs drawn ##
#Param  byteLength   byte length of text array ##
#Param  path         Path providing text baseline ##
#Param  hOffset      distance along path to offset origin ##
#Param  vOffset      offset of text above (if negative) or below (if positive) the path ##
#Param  paint        text size, blend, color, and so on, used to draw ##

#Example
    void draw(SkCanvas* canvas) { 
        const char aero[] = "correo a" "\xC3" "\xA9" "reo";
        const size_t len = sizeof(aero) - 1;
        SkPath path;
        path.addOval({43-26, 43-26, 43+26, 43+26}, SkPath::kCW_Direction, 3);
        SkPaint paint;
        paint.setTextSize(24);
        for (auto offset : { 0, 10, 20 } ) {
            canvas->drawTextOnPathHV(aero, len, path, 0, -offset, paint);
            canvas->translate(70 + offset, 70 + offset);
        }
    }
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawTextOnPath(const void* text, size_t byteLength, const SkPath& path,
                        const SkMatrix* matrix, const SkPaint& paint)

Draw text on Path path, using Clip, Matrix, and Paint paint.

Origin of text is at beginning of path offset by matrix, if provided, before it
is mapped to path. If the path section corresponding the glyph advance is
curved, the glyph is drawn curved to match; control points in the glyph are
mapped to projected points parallel to the path. If the text's advance is larger
than the path length, the excess text is clipped.

text's meaning depends on Paint_Text_Encoding; by default, text encoding is
UTF-8. Origin meaning depends on Paint_Text_Align and Paint_Vertical_Text; by
default text positions the first glyph's left side bearing at origin x and its
baseline at origin y. Text size is affected by Matrix and Paint_Text_Size. 

All elements of paint: Path_Effect, Rasterizer, Mask_Filter, Shader,
Color_Filter, Image_Filter, and Draw_Looper; apply to text. By default, draws
filled 12 point black glyphs.

#Param  text         character code points or glyphs drawn ##
#Param  byteLength   byte length of text array ##
#Param  path         Path providing text baseline ##
#Param  matrix       transform of glyphs before mapping to path; may be nullptr
                     to use identity Matrix.
##
#Param  paint        text size, blend, color, and so on, used to draw ##

#Example
    void draw(SkCanvas* canvas) { 
        const char roller[] = "rollercoaster";
        const size_t len = sizeof(roller) - 1;
        SkPath path;
        path.cubicTo(40, -80, 120, 80, 160, -40);
        SkPaint paint;
        paint.setTextSize(32);
        paint.setStyle(SkPaint::kStroke_Style);
        SkMatrix matrix;
        matrix.setIdentity();
        for (int i = 0; i < 3; ++i) {
            canvas->translate(25, 60);
            canvas->drawPath(path, paint);
            canvas->drawTextOnPath(roller, len, path, &matrix, paint);
            matrix.preTranslate(0, 10);
        }
    }
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawTextRSXform(const void* text, size_t byteLength, const SkRSXform xform[],
                         const SkRect* cullRect, const SkPaint& paint)

Draw text, transforming each glyph by the corresponding SkRSXform,
using Clip, Matrix, and Paint paint.

RSXform array specifies a separate square scale, rotation, and translation for 
each glyph.

Optional Rect cullRect is a conservative bounds of text, taking into account
RSXform and paint. If cullrect is outside of Clip, canvas can skip drawing.

All elements of paint: Path_Effect, Rasterizer, Mask_Filter, Shader,
Color_Filter, Image_Filter, and Draw_Looper; apply to text. By default, draws
filled 12 point black glyphs.

#Param  text         character code points or glyphs drawn ##
#Param  byteLength   byte length of text array ##
#Param  xform        RSXform rotates, scales, and translates each glyph individually ##
#Param  cullRect     Rect bounds of text for efficient clipping; or nullptr ##
#Param  paint        text size, blend, color, and so on, used to draw ##

#Example
void draw(SkCanvas* canvas) {  
    const int iterations = 26;
    SkRSXform transforms[iterations];
    char alphabet[iterations];
    SkScalar angle = 0;
    SkScalar scale = 1;
    for (size_t i = 0; i < SK_ARRAY_COUNT(transforms); ++i) {
        const SkScalar s = SkScalarSin(angle) * scale;
        const SkScalar c = SkScalarCos(angle) * scale;
        transforms[i] = SkRSXform::Make(-c, -s, -s * 16, c * 16);
        angle += .45;
        scale += .2;
        alphabet[i] = 'A' + i;
    }
    SkPaint paint;
    paint.setTextAlign(SkPaint::kCenter_Align);
    canvas->translate(110, 138);
    canvas->drawTextRSXform(alphabet, sizeof(alphabet), transforms, nullptr, paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawTextBlob(const SkTextBlob* blob, SkScalar x, SkScalar y, const SkPaint& paint)

Draw Text_Blob blob at (x, y), using Clip, Matrix, and Paint paint.

blob contains glyphs, their positions, and paint attributes specific to text:
Typeface, Paint_Text_Size, Paint_Text_Scale_X, Paint_Text_Skew_X,
Paint_Text_Align, Paint_Hinting, Anti-alias, Paint_Fake_Bold,
Font_Embedded_Bitmaps, Full_Hinting_Spacing, LCD_Text, Linear_Text,
Subpixel_Text, and Paint_Vertical_Text.

Elements of paint: Path_Effect, Rasterizer, Mask_Filter, Shader, Color_Filter, 
Image_Filter, and Draw_Looper; apply to blob.

#Param  blob     glyphs, positions, and their paints' text size, typeface, and so on ##
#Param  x        horizontal offset applied to blob ##
#Param  y        vertical offset applied to blob ##
#Param  paint    blend, color, stroking, and so on, used to draw ##

#Example
#Height 120
    void draw(SkCanvas* canvas) {
        SkTextBlobBuilder textBlobBuilder;
        const char bunny[] = "/(^x^)\\";
        const int len = sizeof(bunny) - 1;
        uint16_t glyphs[len];
        SkPaint paint;
        paint.textToGlyphs(bunny, len, glyphs);
        int runs[] = { 3, 1, 3 };
        SkPoint textPos = { 20, 100 };
        int glyphIndex = 0;
        for (auto runLen : runs) {
            paint.setTextSize(1 == runLen ? 20 : 50);
            const SkTextBlobBuilder::RunBuffer& run = 
                    textBlobBuilder.allocRun(paint, runLen, textPos.fX, textPos.fY);
            memcpy(run.glyphs, &glyphs[glyphIndex], sizeof(glyphs[0]) * runLen);
            textPos.fX += paint.measureText(&bunny[glyphIndex], runLen, nullptr);
            glyphIndex += runLen;
        }
        sk_sp<const SkTextBlob> blob = textBlobBuilder.make();
        paint.reset();
        canvas->drawTextBlob(blob.get(), 0, 0, paint);
    }
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawTextBlob(const sk_sp<SkTextBlob>& blob, SkScalar x, SkScalar y, const SkPaint& paint) 

Draw Text_Blob blob at (x, y), using Clip, Matrix, and Paint paint.

blob contains glyphs, their positions, and paint attributes specific to text:
Typeface, Paint_Text_Size, Paint_Text_Scale_X, Paint_Text_Skew_X,
Paint_Text_Align, Paint_Hinting, Anti-alias, Paint_Fake_Bold,
Font_Embedded_Bitmaps, Full_Hinting_Spacing, LCD_Text, Linear_Text,
Subpixel_Text, and Paint_Vertical_Text.

Elements of paint: Path_Effect, Rasterizer, Mask_Filter, Shader, Color_Filter, 
Image_Filter, and Draw_Looper; apply to blob.

#Param  blob     glyphs, positions, and their paints' text size, typeface, and so on ##
#Param  x        horizontal offset applied to blob ##
#Param  y        vertical offset applied to blob ##
#Param  paint    blend, color, stroking, and so on, used to draw ##

#Example
#Height 120
#Description
Paint attributes unrelated to text, like color, have no effect on paint in allocated Text_Blob.
Paint attributes related to text, like text size, have no effect on paint passed to drawTextBlob.
##
    void draw(SkCanvas* canvas) {
        SkTextBlobBuilder textBlobBuilder;
        SkPaint paint;
        paint.setTextSize(50);
        paint.setColor(SK_ColorRED);
        const SkTextBlobBuilder::RunBuffer& run = 
                textBlobBuilder.allocRun(paint, 1, 20, 100);
        run.glyphs[0] = 20;
        sk_sp<const SkTextBlob> blob = textBlobBuilder.make();
        paint.setTextSize(10);
        paint.setColor(SK_ColorBLUE);
        canvas->drawTextBlob(blob.get(), 0, 0, paint);
    }
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawPicture(const SkPicture* picture) 

Draw Picture picture, using Clip and Matrix.
Clip and Matrix are unchanged by picture contents, as if
save() was called before and restore() was called after drawPicture.

Picture records a series of draw commands for later playback.

#Param  picture  recorded drawing commands to play ##

#Example
void draw(SkCanvas* canvas) {  
    SkPictureRecorder recorder;
    SkCanvas* recordingCanvas = recorder.beginRecording(50, 50);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, 0xff007f00 } ) {
        SkPaint paint;
        paint.setColor(color);
        recordingCanvas->drawRect({10, 10, 30, 40}, paint);
        recordingCanvas->translate(10, 10);
        recordingCanvas->scale(1.2f, 1.4f);
    }
    sk_sp<SkPicture> playback = recorder.finishRecordingAsPicture();
    const SkPicture* playbackPtr = playback.get();
    canvas->drawPicture(playback);
    canvas->scale(2, 2);
    canvas->translate(50, 0);
    canvas->drawPicture(playback);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawPicture(const sk_sp<SkPicture>& picture) 

Draw Picture picture, using Clip and Matrix.
Clip and Matrix are unchanged by picture contents, as if
save() was called before and restore() was called after drawPicture.

Picture records a series of draw commands for later playback.

#Param  picture  recorded drawing commands to play ##

#Example
void draw(SkCanvas* canvas) {  
    SkPictureRecorder recorder;
    SkCanvas* recordingCanvas = recorder.beginRecording(50, 50);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, 0xff007f00 } ) {
        SkPaint paint;
        paint.setColor(color);
        recordingCanvas->drawRect({10, 10, 30, 40}, paint);
        recordingCanvas->translate(10, 10);
        recordingCanvas->scale(1.2f, 1.4f);
    }
    sk_sp<SkPicture> playback = recorder.finishRecordingAsPicture();
    canvas->drawPicture(playback);
    canvas->scale(2, 2);
    canvas->translate(50, 0);
    canvas->drawPicture(playback);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawPicture(const SkPicture* picture, const SkMatrix* matrix, const SkPaint* paint)

Draw Picture picture, using Clip and Matrix; transforming picture with
Matrix matrix, if provided; and use Paint paint Color_Alpha, Color_Filter,
Image_Filter, and Blend_Mode, if provided.

matrix transformation is equivalent to: save(), concat(), drawPicture, restore().
paint use is equivalent to: saveLayer, drawPicture, restore().

#Param  picture  recorded drawing commands to play ##
#Param  matrix   Matrix to rotate, scale, translate, and so on; may be nullptr ##
#Param  paint    Paint to apply transparency, filtering, and so on; may be nullptr ##

#Example
void draw(SkCanvas* canvas) {  
    SkPaint paint;
    SkPictureRecorder recorder;
    SkCanvas* recordingCanvas = recorder.beginRecording(50, 50);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, 0xff007f00 } ) {
        paint.setColor(color);
        recordingCanvas->drawRect({10, 10, 30, 40}, paint);
        recordingCanvas->translate(10, 10);
        recordingCanvas->scale(1.2f, 1.4f);
    }
    sk_sp<SkPicture> playback = recorder.finishRecordingAsPicture();
    const SkPicture* playbackPtr = playback.get();
    SkMatrix matrix;
    matrix.reset();
    for (auto alpha : { 70, 140, 210 } ) {
    paint.setAlpha(alpha);
    canvas->drawPicture(playbackPtr, &matrix, &paint);
    matrix.preTranslate(70, 70);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawPicture(const sk_sp<SkPicture>& picture, const SkMatrix* matrix, const SkPaint* paint) 

Draw Picture picture, using Clip and Matrix; transforming picture with
Matrix matrix, if provided; and use Paint paint Color_Alpha, Color_Filter,
Image_Filter, and Blend_Mode, if provided.

matrix transformation is equivalent to: save(), concat(), drawPicture, restore().
paint use is equivalent to: saveLayer, drawPicture, restore().

#Param  picture  recorded drawing commands to play ##
#Param  matrix   Matrix to rotate, scale, translate, and so on; may be nullptr ##
#Param  paint    Paint to apply transparency, filtering, and so on; may be nullptr ##

#Example
void draw(SkCanvas* canvas) {  
    SkPaint paint;
    SkPictureRecorder recorder;
    SkCanvas* recordingCanvas = recorder.beginRecording(50, 50);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, 0xff007f00 } ) {
        paint.setColor(color);
        recordingCanvas->drawRect({10, 10, 30, 40}, paint);
        recordingCanvas->translate(10, 10);
        recordingCanvas->scale(1.2f, 1.4f);
    }
    sk_sp<SkPicture> playback = recorder.finishRecordingAsPicture();
    SkMatrix matrix;
    matrix.reset();
    for (auto alpha : { 70, 140, 210 } ) {
    paint.setAlpha(alpha);
    canvas->drawPicture(playback, &matrix, &paint);
    matrix.preTranslate(70, 70);
    }
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawVertices(const SkVertices* vertices, SkBlendMode mode, const SkPaint& paint)

Draw Vertices vertices, a triangle mesh, using Clip and Matrix.
If Vertices_Texs and Vertices_Colors are defined in vertices, and Paint paint
contains Shader, Blend_Mode mode combines Vertices_Colors with Shader.

#Param  vertices  triangle mesh to draw ##
#Param  mode      combines Vertices_Colors with Shader, if both are present ##
#Param  paint     specifies the Shader, used as Vertices texture; may be nullptr ##

#Example
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkPoint points[] = { { 0, 0 }, { 250, 0 }, { 100, 100 }, { 0, 250 } };
    SkColor colors[] = { SK_ColorRED, SK_ColorBLUE, SK_ColorYELLOW, SK_ColorCYAN };
    auto vertices = SkVertices::MakeCopy(SkVertices::kTriangleFan_VertexMode,
            SK_ARRAY_COUNT(points), points, nullptr, colors);
    canvas->drawVertices(vertices.get(), SkBlendMode::kSrc, paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawVertices(const sk_sp<SkVertices>& vertices, SkBlendMode mode, const SkPaint& paint)

Draw Vertices vertices, a triangle mesh, using Clip and Matrix.
If Vertices_Texs and Vertices_Colors are defined in vertices, and Paint paint
contains Shader, Blend_Mode mode combines Vertices_Colors with Shader.

#Param  vertices  triangle mesh to draw ##
#Param  mode      combines Vertices_Colors with Shader, if both are present ##
#Param  paint     specifies the Shader, used as Vertices texture, may be nullptr ##

#Example
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkPoint points[] = { { 0, 0 }, { 250, 0 }, { 100, 100 }, { 0, 250 } };
    SkPoint texs[] = { { 0, 0 }, { 0, 250 }, { 250, 250 }, { 250, 0 } };
    SkColor colors[] = { SK_ColorRED, SK_ColorBLUE, SK_ColorYELLOW, SK_ColorCYAN };
    paint.setShader(SkGradientShader::MakeLinear(points, colors, nullptr, 4,
            SkShader::kClamp_TileMode));
    auto vertices = SkVertices::MakeCopy(SkVertices::kTriangleFan_VertexMode,
            SK_ARRAY_COUNT(points), points, texs, colors);
    canvas->drawVertices(vertices.get(), SkBlendMode::kDarken, paint);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawPatch(const SkPoint cubics[12], const SkColor colors[4],
                   const SkPoint texCoords[4], SkBlendMode mode, const SkPaint& paint)

Draw a cubic Coons patch: the interpolation of four cubics with shared corners, 
associating a color, and optionally a texture coordinate, with each corner.

The Coons patch uses Clip and Matrix, Paint paint's Shader, Color_Filter,
Color_Alpha, Image_Filter, and Blend_Mode. If Shader is provided it is treated
as the Coons patch texture; Blend_Mode mode combines Color colors and Shader if
both are provided.

Point array cubics specifies four cubics starting at the top left corner, 
in clockwise order, sharing every fourth point. The last cubic ends at the
first point.

Color array color associates colors with corners in top left, top right,
bottom right, bottom left order.

If paint contains Shader, Point array texCoords maps Shader as texture to
corners in top left, top right, bottom right, bottom left order.

#Param cubics     Cubic array, sharing common points ##
#Param colors     Color array, one for each corner ##
#Param texCoords  Point array of texure coordinates, mapping Shader to corners;
                  may be nullptr 
#Param ##
#Param mode       Blend_Mode for colors, and for Shader if paint has one ##
#Param paint      Shader, Color_Filter, Blend_Mode, used to draw ##

#Example
#Image 5
void draw(SkCanvas* canvas) {
    // SkBitmap source = cmbkygk;
    SkPaint paint;
    paint.setFilterQuality(kLow_SkFilterQuality);
    paint.setAntiAlias(true);
    SkPoint cubics[] = { { 3, 1 },    { 4, 2 }, { 5, 1 },    { 7, 3 },
                      /* { 7, 3 }, */ { 6, 4 }, { 7, 5 },    { 5, 7 },
                      /* { 5, 7 }, */ { 4, 6 }, { 3, 7 },    { 1, 5 },
                      /* { 1, 5 }, */ { 2, 4 }, { 1, 3 }, /* { 3, 1 } */ };
    SkColor colors[] = { 0xbfff0000, 0xbf0000ff, 0xbfff00ff, 0xbf00ffff };
    SkPoint texCoords[] = { { -30, -30 }, { 162, -30}, { 162, 162}, { -30, 162} };
    paint.setShader(SkShader::MakeBitmapShader(source, SkShader::kClamp_TileMode,
                                                       SkShader::kClamp_TileMode, nullptr));
    canvas->scale(15, 15);
    for (auto blend : { SkBlendMode::kSrcOver, SkBlendMode::kModulate, SkBlendMode::kXor } ) {
        canvas->drawPatch(cubics, colors, texCoords, blend, paint);
        canvas->translate(4, 4);
    }
}
##

#ToDo incomplete; can patch use image filter? ##

##

# ------------------------------------------------------------------------------

#Method void drawPatch(const SkPoint cubics[12], const SkColor colors[4],
                   const SkPoint texCoords[4], const SkPaint& paint) 

Draw a cubic Coons patch: the interpolation of four cubics with shared corners, 
associating a color, and optionally a texture coordinate, with each corner.

The Coons patch uses Clip and Matrix, Paint paint's Shader, Color_Filter,
Color_Alpha, Image_Filter, and Blend_Mode. If Shader is provided it is treated
as the Coons patch texture; Blend_Mode mode combines Color colors and Shader if
both are provided.

Point array cubics specifies four cubics starting at the top left corner, 
in clockwise order, sharing every fourth point. The last cubic ends at the
first point.

Color array color associates colors with corners in top left, top right,
bottom right, bottom left order.

If paint contains Shader, Point array texCoords maps Shader as texture to
corners in top left, top right, bottom right, bottom left order.

#Param cubics     Cubic array, sharing common points ##
#Param colors     Color array, one for each corner ##
#Param texCoords  Point array of texure coordinates, mapping Shader to corners;
                  may be nullptr 
#Param ##
#Param paint      Shader, Color_Filter, Blend_Mode, used to draw ##

#Example
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    SkPoint cubics[] = { { 3, 1 },    { 4, 2 }, { 5, 1 },    { 7, 3 },
                      /* { 7, 3 }, */ { 6, 4 }, { 7, 5 },    { 5, 7 },
                      /* { 5, 7 }, */ { 4, 6 }, { 3, 7 },    { 1, 5 },
                      /* { 1, 5 }, */ { 2, 4 }, { 1, 3 }, /* { 3, 1 } */ };
    SkColor colors[] = { SK_ColorRED, SK_ColorBLUE, SK_ColorYELLOW, SK_ColorCYAN };
    canvas->scale(30, 30);
    canvas->drawPatch(cubics, colors, nullptr, paint);
    SkPoint text[] = { {3,0.9f}, {4,2.5f}, {5,0.9f}, {7.5f,3.2f}, {5.5f,4.2f},
            {7.5f,5.2f}, {5,7.5f}, {4,5.9f}, {3,7.5f}, {0.5f,5.2f}, {2.5f,4.2f},
            {0.5f,3.2f} };
    paint.setTextSize(18.f / 30);
    paint.setTextAlign(SkPaint::kCenter_Align);
    for (int i = 0; i< 10; ++i) {
       char digit = '0' + i;
       canvas->drawText(&digit, 1, text[i].fX, text[i].fY, paint);
    }
    canvas->drawString("10", text[10].fX, text[10].fY, paint);
    canvas->drawString("11", text[11].fX, text[11].fY, paint);
    paint.setStyle(SkPaint::kStroke_Style);
    canvas->drawPoints(SkCanvas::kPolygon_PointMode, 12, cubics, paint);
    canvas->drawLine(cubics[11].fX, cubics[11].fY, cubics[0].fX, cubics[0].fY, paint);
}
##

#Example
#Image 6
void draw(SkCanvas* canvas) {
    // SkBitmap source = checkerboard;
    SkPaint paint;
    paint.setFilterQuality(kLow_SkFilterQuality);
    paint.setAntiAlias(true);
    SkPoint cubics[] = { { 3, 1 },    { 4, 2 }, { 5, 1 },    { 7, 3 },
                      /* { 7, 3 }, */ { 6, 4 }, { 7, 5 },    { 5, 7 },
                      /* { 5, 7 }, */ { 4, 6 }, { 3, 7 },    { 1, 5 },
                      /* { 1, 5 }, */ { 2, 4 }, { 1, 3 }, /* { 3, 1 } */ };
    SkPoint texCoords[] = { { 0, 0 }, { 0, 62}, { 62, 62}, { 62, 0 } };
    paint.setShader(SkShader::MakeBitmapShader(source, SkShader::kClamp_TileMode,
                                                       SkShader::kClamp_TileMode, nullptr));
    canvas->scale(30, 30);
    canvas->drawPatch(cubics, nullptr, texCoords, paint);
}
##

#ToDo incomplete; can patch use image filter? ##

##

# ------------------------------------------------------------------------------

#Method void drawAtlas(const SkImage* atlas, const SkRSXform xform[], const SkRect tex[],
                   const SkColor colors[], int count, SkBlendMode mode, const SkRect* cullRect,
                   const SkPaint* paint)

Draw a set of sprites from atlas, using Clip, Matrix, and optional Paint paint.
paint uses Anti-alias, Color_Alpha, Color_Filter, Image_Filter, and Blend_Mode
to draw, if present. For each entry in the array, Rect tex locates sprite in
atlas, and RSXform xform transforms it into destination space.

xform, text, and colors if present, must contain count entries.
Optional colors are applied for each sprite using Blend_Mode.
Optional cullRect is a conservative bounds of all transformed sprites. 
If cullrect is outside of Clip, canvas can skip drawing.

#Param atlas  Image containing sprites ##
#Param xform  RSXform mappings for sprites in atlas ##
#Param tex    Rect locations of sprites in atlas ##
#Param colors  Color, one per sprite, blended with sprite using Blend_Mode; may be nullptr ##
#Param count  number of sprites to draw ##
#Param mode   Blend_Mode combining colors and sprites ##
#Param cullRect  Rect bounds of transformed sprites for efficient clipping; may be nullptr ##
#Param paint  Paint Color_Filter, Image_Filter, Blend_Mode, and so on; may be nullptr ##

#Example
#Image 3
void draw(SkCanvas* canvas) {
  // SkBitmap source = mandrill;
  SkRSXform xforms[] = { { .5f, 0, 0, 0 }, {0, .5f, 200, 100 } };
  SkRect tex[] = { { 0, 0, 250, 250 }, { 0, 0, 250, 250 } };
  SkColor colors[] = { 0x7f55aa00, 0x7f3333bf };
  const SkImage* imagePtr = image.get();
  canvas->drawAtlas(imagePtr, xforms, tex, colors, 2, SkBlendMode::kSrcOver, nullptr, nullptr);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawAtlas(const sk_sp<SkImage>& atlas, const SkRSXform xform[], const SkRect tex[],
                   const SkColor colors[], int count, SkBlendMode mode, const SkRect* cullRect,
                   const SkPaint* paint) 

Draw a set of sprites from atlas, using Clip, Matrix, and optional Paint paint.
paint uses Anti-alias, Color_Alpha, Color_Filter, Image_Filter, and Blend_Mode
to draw, if present. For each entry in the array, Rect tex locates sprite in
atlas, and RSXform xform transforms it into destination space.

xform, text, and colors if present, must contain count entries.
Optional colors is applied for each sprite using Blend_Mode.
Optional cullRect is a conservative bounds of all transformed sprites. 
If cullrect is outside of Clip, canvas can skip drawing.

#Param atlas  Image containing sprites ##
#Param xform  RSXform mappings for sprites in atlas ##
#Param tex    Rect locations of sprites in atlas ##
#Param colors  Color, one per sprite, blended with sprite using Blend_Mode; may be nullptr ##
#Param count  number of sprites to draw ##
#Param mode   Blend_Mode combining colors and sprites ##
#Param cullRect  Rect bounds of transformed sprites for efficient clipping; may be nullptr ##
#Param paint  Paint Color_Filter, Image_Filter, Blend_Mode, and so on; may be nullptr ##

#Example
#Image 3
void draw(SkCanvas* canvas) {
  // SkBitmap source = mandrill;
  SkRSXform xforms[] = { { .5f, 0, 0, 0 }, {0, .5f, 200, 100 } };
  SkRect tex[] = { { 0, 0, 250, 250 }, { 0, 0, 250, 250 } };
  SkColor colors[] = { 0x7f55aa00, 0x7f3333bf };
  SkPaint paint;
  paint.setAlpha(127);
  canvas->drawAtlas(image, xforms, tex, colors, 2, SkBlendMode::kPlus, nullptr, &paint);
}
##

#ToDo bug in example on cpu side, gpu looks ok ##

##

# ------------------------------------------------------------------------------

#Method void drawAtlas(const SkImage* atlas, const SkRSXform xform[], const SkRect tex[], int count,
                   const SkRect* cullRect, const SkPaint* paint) 

Draw a set of sprites from atlas, using Clip, Matrix, and optional Paint paint.
paint uses Anti-alias, Color_Alpha, Color_Filter, Image_Filter, and Blend_Mode
to draw, if present. For each entry in the array, Rect tex locates sprite in
atlas, and RSXform xform transforms it into destination space.

xform and text must contain count entries.
Optional cullRect is a conservative bounds of all transformed sprites. 
If cullrect is outside of Clip, canvas can skip drawing.

#Param atlas  Image containing sprites ##
#Param xform  RSXform mappings for sprites in atlas ##
#Param tex    Rect locations of sprites in atlas ##
#Param count  number of sprites to draw ##
#Param cullRect  Rect bounds of transformed sprites for efficient clipping; may be nullptr ##
#Param paint  Paint Color_Filter, Image_Filter, Blend_Mode, and so on; may be nullptr ##

#Example
#Image 3
void draw(SkCanvas* canvas) {
  // sk_sp<SkImage> image = mandrill;
  SkRSXform xforms[] = { { .5f, 0, 0, 0 }, {0, .5f, 200, 100 } };
  SkRect tex[] = { { 0, 0, 250, 250 }, { 0, 0, 250, 250 } };
  const SkImage* imagePtr = image.get();
  canvas->drawAtlas(imagePtr, xforms, tex, 2, nullptr, nullptr);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawAtlas(const sk_sp<SkImage>& atlas, const SkRSXform xform[], const SkRect tex[],
                   int count, const SkRect* cullRect, const SkPaint* paint) 

Draw a set of sprites from atlas, using Clip, Matrix, and optional Paint paint.
paint uses Anti-alias, Color_Alpha, Color_Filter, Image_Filter, and Blend_Mode
to draw, if present. For each entry in the array, Rect tex locates sprite in
atlas, and RSXform xform transforms it into destination space.

xform and text must contain count entries.
Optional cullRect is a conservative bounds of all transformed sprites. 
If cullrect is outside of Clip, canvas can skip drawing.

#Param atlas  Image containing sprites ##
#Param xform  RSXform mappings for sprites in atlas ##
#Param tex    Rect locations of sprites in atlas ##
#Param count  number of sprites to draw ##
#Param cullRect  Rect bounds of transformed sprites for efficient clipping; may be nullptr ##
#Param paint  Paint Color_Filter, Image_Filter, Blend_Mode, and so on; may be nullptr ##

#Example
#Image 3
void draw(SkCanvas* canvas) {
  // sk_sp<SkImage> image = mandrill;
  SkRSXform xforms[] = { { 1, 0, 0, 0 }, {0, 1, 300, 100 } };
  SkRect tex[] = { { 0, 0, 200, 200 }, { 200, 0, 400, 200 } };
  canvas->drawAtlas(image, xforms, tex, 2, nullptr, nullptr);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawDrawable(SkDrawable* drawable, const SkMatrix* matrix = NULL)

Draw Drawable drawable using Clip and Matrix, concatenated with 
optional matrix.

If Canvas has an asynchronous implementation, as is the case 
when it is recording into Picture, then drawable will be referenced,
so that SkDrawable::draw() can be called when the operation is finalized. To force
immediate drawing, call SkDrawable::draw() instead.

#Param drawable  custom struct encapsulating drawing commands ##
#Param matrix    transformation applied to drawing; may be nullptr  ##

#Example
#Height 100
#Function
struct MyDrawable : public SkDrawable {
    SkRect onGetBounds() override { return SkRect::MakeWH(50, 100);  }

    void onDraw(SkCanvas* canvas) override {
       SkPath path;
       path.conicTo(10, 90, 50, 90, 0.9f);
       SkPaint paint;
       paint.setColor(SK_ColorBLUE);
       canvas->drawRect(path.getBounds(), paint);
       paint.setAntiAlias(true);
       paint.setColor(SK_ColorWHITE);
       canvas->drawPath(path, paint);
    }
};

#Function ##
void draw(SkCanvas* canvas) {
    sk_sp<SkDrawable> drawable(new MyDrawable);
  SkMatrix matrix;
  matrix.setTranslate(10, 10);
  canvas->drawDrawable(drawable.get(), &matrix);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawDrawable(SkDrawable* drawable, SkScalar x, SkScalar y)

Draw Drawable drawable using Clip and Matrix, offset by (x, y).

If Canvas has an asynchronous implementation, as is the case 
when it is recording into Picture, then drawable will be referenced,
so that SkDrawable::draw() can be called when the operation is finalized. To force
immediate drawing, call SkDrawable::draw() instead.

#Param drawable  custom struct encapsulating drawing commands ##
#Param x  offset into Canvas writable pixels in x ##
#Param y  offset into Canvas writable pixels in y ##

#Example
#Height 100
#Function
struct MyDrawable : public SkDrawable {
    SkRect onGetBounds() override { return SkRect::MakeWH(50, 100);  }

    void onDraw(SkCanvas* canvas) override {
       SkPath path;
       path.conicTo(10, 90, 50, 90, 0.9f);
       SkPaint paint;
       paint.setColor(SK_ColorBLUE);
       canvas->drawRect(path.getBounds(), paint);
       paint.setAntiAlias(true);
       paint.setColor(SK_ColorWHITE);
       canvas->drawPath(path, paint);
    }
};

#Function ##
void draw(SkCanvas* canvas) {
    sk_sp<SkDrawable> drawable(new MyDrawable);
  canvas->drawDrawable(drawable.get(), 10, 10);
}
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawAnnotation(const SkRect& rect, const char key[], SkData* value)

Associate Rect on Canvas when an annotation; a key-value pair, where the key is
a null-terminated utf8 string, and optional value is stored as Data.

Only some canvas implementations, such as recording to Picture, or drawing to 
Document_PDF, use annotations.

#Param rect    Rect extent of canvas to annotate ##
#Param key     string used for lookup ##
#Param value   data holding value stored in annotation ##

#Example
    #Height 1
    const char text[] = "Click this link!";
    SkRect bounds;
    SkPaint paint;
    paint.setTextSize(40);
    (void)paint.measureText(text, strlen(text), &bounds);
    const char url[] = "https://www.google.com/";
    sk_sp<SkData> urlData(SkData::MakeWithCString(url));
    canvas->drawAnnotation(bounds, "url_key", urlData.get());
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method void drawAnnotation(const SkRect& rect, const char key[], const sk_sp<SkData>& value) 

Associate Rect on Canvas when an annotation; a key-value pair, where the key is
a null-terminated utf8 string, and optional value is stored as Data.

Only some canvas implementations, such as recording to Picture, or drawing to 
Document_PDF, use annotations.

#Param rect    Rect extent of canvas to annotate ##
#Param key     string used for lookup ##
#Param value   data holding value stored in annotation ##

#Example
#Height 1
    const char text[] = "Click this link!";
    SkRect bounds;
    SkPaint paint;
    paint.setTextSize(40);
    (void)paint.measureText(text, strlen(text), &bounds);
    const char url[] = "https://www.google.com/";
    sk_sp<SkData> urlData(SkData::MakeWithCString(url));
    canvas->drawAnnotation(bounds, "url_key", urlData.get());
##

#ToDo incomplete ##

##

#Method SkDrawFilter* getDrawFilter() const

Legacy call to be deprecated.

#Deprecated 
##

##

#Method virtual SkDrawFilter* setDrawFilter(SkDrawFilter* filter)

Legacy call to be deprecated.

#Deprecated 
##

##

# ------------------------------------------------------------------------------

#Method virtual bool isClipEmpty() const

Returns true if Clip is empty; that is, nothing will draw.

May do work when called; it should not be called
more often than needed. However, once called, subsequent calls perform no
work until Clip changes.

#Return  true if Clip is empty ##

#Example
    void draw(SkCanvas* canvas) {
        SkDebugf("clip is%s empty\n", canvas->isClipEmpty() ? "" : " not");
        SkPath path;
        canvas->clipPath(path);
        SkDebugf("clip is%s empty\n", canvas->isClipEmpty() ? "" : " not");
    }
    #StdOut
        clip is not empty
        clip is empty
    ##
##

#ToDo incomplete ##

##

# ------------------------------------------------------------------------------

#Method virtual bool isClipRect() const

Returns true if Clip is Rect and not empty.
Returns false if the clip is empty, or if it is not Rect.

#Return  true if Clip is Rect and not empty ##

#Example
    void draw(SkCanvas* canvas) {
        SkDebugf("clip is%s rect\n", canvas->isClipRect() ? "" : " not");
        canvas->clipRect({0, 0, 0, 0});
        SkDebugf("clip is%s rect\n", canvas->isClipRect() ? "" : " not");
    }
    #StdOut
        clip is rect
        clip is not rect
    ##
##

#ToDo incomplete ##

##

#Class SkCanvas ##
#Topic Canvas ##