include/core/SkShader.h

/*
 * Copyright 2006 The Android Open Source Project
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef SkShader_DEFINED
#define SkShader_DEFINED

#include "SkBitmap.h"
#include "SkFlattenable.h"
#include "SkMask.h"
#include "SkMatrix.h"
#include "SkPaint.h"
#include "../gpu/GrColor.h"

class SkPath;
class SkPicture;
class SkXfermode;
class GrContext;
class GrFragmentProcessor;
class GrProcessorDataManager;

/** \class SkShader
 *
 *  Shaders specify the source color(s) for what is being drawn. If a paint
 *  has no shader, then the paint's color is used. If the paint has a
 *  shader, then the shader's color(s) are use instead, but they are
 *  modulated by the paint's alpha. This makes it easy to create a shader
 *  once (e.g. bitmap tiling or gradient) and then change its transparency
 *  w/o having to modify the original shader... only the paint's alpha needs
 *  to be modified.
 */
class SK_API SkShader : public SkFlattenable {
public:
    SkShader(const SkMatrix* localMatrix = NULL);
    virtual ~SkShader();

    /**
     *  Returns the local matrix.
     *
     *  FIXME: This can be incorrect for a Shader with its own local matrix
     *  that is also wrapped via CreateLocalMatrixShader.
     */
    const SkMatrix& getLocalMatrix() const { return fLocalMatrix; }

    enum TileMode {
        /** replicate the edge color if the shader draws outside of its
         *  original bounds
         */
        kClamp_TileMode,

        /** repeat the shader's image horizontally and vertically */
        kRepeat_TileMode,

        /** repeat the shader's image horizontally and vertically, alternating
         *  mirror images so that adjacent images always seam
         */
        kMirror_TileMode,

#if 0
        /** only draw within the original domain, return 0 everywhere else */
        kDecal_TileMode,
#endif
    };

    enum {
        kTileModeCount = kMirror_TileMode + 1
    };

    // override these in your subclass

    enum Flags {
        //!< set if all of the colors will be opaque
        kOpaqueAlpha_Flag  = 0x01,

        //! set if this shader's shadeSpan16() method can be called
        kHasSpan16_Flag = 0x02,

        /** Set this bit if the shader's native data type is instrinsically 16
            bit, meaning that calling the 32bit shadeSpan() entry point will
            mean the the impl has to up-sample 16bit data into 32bit. Used as a
            a means of clearing a dither request if the it will have no effect
        */
        kIntrinsicly16_Flag = 0x04,

        /** set if the spans only vary in X (const in Y).
            e.g. an Nx1 bitmap that is being tiled in Y, or a linear-gradient
            that varies from left-to-right. This flag specifies this for
            shadeSpan().
         */
        kConstInY32_Flag = 0x08,

        /** same as kConstInY32_Flag, but is set if this is true for shadeSpan16
            which may not always be the case, since shadeSpan16 may be
            predithered, which would mean it was not const in Y, even though
            the 32bit shadeSpan() would be const.
         */
        kConstInY16_Flag = 0x10
    };

    /**
     *  Returns true if the shader is guaranteed to produce only opaque
     *  colors, subject to the SkPaint using the shader to apply an opaque
     *  alpha value. Subclasses should override this to allow some
     *  optimizations.
     */
    virtual bool isOpaque() const { return false; }

    /**
     *  ContextRec acts as a parameter bundle for creating Contexts.
     */
    struct ContextRec {
        ContextRec(const SkPaint& paint, const SkMatrix& matrix, const SkMatrix* localM)
            : fPaint(&paint)
            , fMatrix(&matrix)
            , fLocalMatrix(localM) {}

        const SkPaint*  fPaint;         // the current paint associated with the draw
        const SkMatrix* fMatrix;        // the current matrix in the canvas
        const SkMatrix* fLocalMatrix;   // optional local matrix
    };

    class Context : public ::SkNoncopyable {
    public:
        Context(const SkShader& shader, const ContextRec&);

        virtual ~Context();

        /**
         *  Called sometimes before drawing with this shader. Return the type of
         *  alpha your shader will return. The default implementation returns 0.
         *  Your subclass should override if it can (even sometimes) report a
         *  non-zero value, since that will enable various blitters to perform
         *  faster.
         */
        virtual uint32_t getFlags() const { return 0; }

        /**
         *  Return the alpha associated with the data returned by shadeSpan16(). If
         *  kHasSpan16_Flag is not set, this value is meaningless.
         */
        virtual uint8_t getSpan16Alpha() const { return fPaintAlpha; }

        /**
         *  Called for each span of the object being drawn. Your subclass should
         *  set the appropriate colors (with premultiplied alpha) that correspond
         *  to the specified device coordinates.
         */
        virtual void shadeSpan(int x, int y, SkPMColor[], int count) = 0;

        typedef void (*ShadeProc)(void* ctx, int x, int y, SkPMColor[], int count);
        virtual ShadeProc asAShadeProc(void** ctx);

        /**
         *  Called only for 16bit devices when getFlags() returns
         *  kOpaqueAlphaFlag | kHasSpan16_Flag
         */
        virtual void shadeSpan16(int x, int y, uint16_t[], int count);

        /**
         *  Similar to shadeSpan, but only returns the alpha-channel for a span.
         *  The default implementation calls shadeSpan() and then extracts the alpha
         *  values from the returned colors.
         */
        virtual void shadeSpanAlpha(int x, int y, uint8_t alpha[], int count);

        /**
         *  Helper function that returns true if this shader's shadeSpan16() method
         *  can be called.
         */
        bool canCallShadeSpan16() {
            return SkShader::CanCallShadeSpan16(this->getFlags());
        }

        // Notification from blitter::blitMask in case we need to see the non-alpha channels
        virtual void set3DMask(const SkMask*) {}

    protected:
        // Reference to shader, so we don't have to dupe information.
        const SkShader& fShader;

        enum MatrixClass {
            kLinear_MatrixClass,            // no perspective
            kFixedStepInX_MatrixClass,      // fast perspective, need to call fixedStepInX() each
                                            // scanline
            kPerspective_MatrixClass        // slow perspective, need to mappoints each pixel
        };
        static MatrixClass ComputeMatrixClass(const SkMatrix&);

        uint8_t         getPaintAlpha() const { return fPaintAlpha; }
        const SkMatrix& getTotalInverse() const { return fTotalInverse; }
        MatrixClass     getInverseClass() const { return (MatrixClass)fTotalInverseClass; }
        const SkMatrix& getCTM() const { return fCTM; }
    private:
        SkMatrix    fCTM;
        SkMatrix    fTotalInverse;
        uint8_t     fPaintAlpha;
        uint8_t     fTotalInverseClass;

        typedef SkNoncopyable INHERITED;
    };

    /**
     *  Create the actual object that does the shading.
     *  Size of storage must be >= contextSize.
     */
    Context* createContext(const ContextRec&, void* storage) const;

    /**
     *  Return the size of a Context returned by createContext.
     *
     *  Override this if your subclass overrides createContext, to return the correct size of
     *  your subclass' context.
     */
    virtual size_t contextSize() const;

    /**
     *  Helper to check the flags to know if it is legal to call shadeSpan16()
     */
    static bool CanCallShadeSpan16(uint32_t flags) {
        return (flags & kHasSpan16_Flag) != 0;
    }

    /**
     *  Returns true if this shader is just a bitmap, and if not null, returns the bitmap,
     *  localMatrix, and tilemodes. If this is not a bitmap, returns false and ignores the
     *  out-parameters.
     */
    bool isABitmap(SkBitmap* outTexture, SkMatrix* outMatrix, TileMode xy[2]) const {
        return this->onIsABitmap(outTexture, outMatrix, xy);
    }

    bool isABitmap() const {
        return this->isABitmap(nullptr, nullptr, nullptr);
    }

    /**
     *  If the shader subclass can be represented as a gradient, asAGradient
     *  returns the matching GradientType enum (or kNone_GradientType if it
     *  cannot). Also, if info is not null, asAGradient populates info with
     *  the relevant (see below) parameters for the gradient.  fColorCount
     *  is both an input and output parameter.  On input, it indicates how
     *  many entries in fColors and fColorOffsets can be used, if they are
     *  non-NULL.  After asAGradient has run, fColorCount indicates how
     *  many color-offset pairs there are in the gradient.  If there is
     *  insufficient space to store all of the color-offset pairs, fColors
     *  and fColorOffsets will not be altered.  fColorOffsets specifies
     *  where on the range of 0 to 1 to transition to the given color.
     *  The meaning of fPoint and fRadius is dependant on the type of gradient.
     *
     *  None:
     *      info is ignored.
     *  Color:
     *      fColorOffsets[0] is meaningless.
     *  Linear:
     *      fPoint[0] and fPoint[1] are the end-points of the gradient
     *  Radial:
     *      fPoint[0] and fRadius[0] are the center and radius
     *  Conical:
     *      fPoint[0] and fRadius[0] are the center and radius of the 1st circle
     *      fPoint[1] and fRadius[1] are the center and radius of the 2nd circle
     *  Sweep:
     *      fPoint[0] is the center of the sweep.
     */

    enum GradientType {
        kNone_GradientType,
        kColor_GradientType,
        kLinear_GradientType,
        kRadial_GradientType,
        kSweep_GradientType,
        kConical_GradientType,
        kLast_GradientType = kConical_GradientType
    };

    struct GradientInfo {
        int         fColorCount;    //!< In-out parameter, specifies passed size
                                    //   of fColors/fColorOffsets on input, and
                                    //   actual number of colors/offsets on
                                    //   output.
        SkColor*    fColors;        //!< The colors in the gradient.
        SkScalar*   fColorOffsets;  //!< The unit offset for color transitions.
        SkPoint     fPoint[2];      //!< Type specific, see above.
        SkScalar    fRadius[2];     //!< Type specific, see above.
        TileMode    fTileMode;      //!< The tile mode used.
        uint32_t    fGradientFlags; //!< see SkGradientShader::Flags
    };

    virtual GradientType asAGradient(GradientInfo* info) const;

    /**
     *  If the shader subclass is composed of two shaders, return true, and if rec is not NULL,
     *  fill it out with info about the shader.
     *
     *  These are bare pointers; the ownership and reference count are unchanged.
     */

    struct ComposeRec {
        const SkShader*     fShaderA;
        const SkShader*     fShaderB;
        const SkXfermode*   fMode;
    };

    virtual bool asACompose(ComposeRec*) const { return false; }


    /**
     *  Returns a GrFragmentProcessor that implements the shader for the GPU backend. NULL is
     *  returned if there is no GPU implementation.
     *
     *  The GPU device does not call SkShader::createContext(), instead we pass the view matrix,
     *  local matrix, and filter quality directly.
     *
     *  The GrContext may be used by the to create textures that are required by the returned
     *  processor.
     */
    virtual const GrFragmentProcessor* asFragmentProcessor(GrContext*,
                                                           const SkMatrix& viewMatrix,
                                                           const SkMatrix* localMatrix,
                                                           SkFilterQuality,
                                                           GrProcessorDataManager*) const;

    /**
     *  If the shader can represent its "average" luminance in a single color, return true and
     *  if color is not NULL, return that color. If it cannot, return false and ignore the color
     *  parameter.
     *
     *  Note: if this returns true, the returned color will always be opaque, as only the RGB
     *  components are used to compute luminance.
     */
    bool asLuminanceColor(SkColor*) const;

#ifdef SK_BUILD_FOR_ANDROID_FRAMEWORK
    /**
     *  If the shader is a custom shader which has data the caller might want, call this function
     *  to get that data.
     */
    virtual bool asACustomShader(void** /* customData */) const { return false; }
#endif

    //////////////////////////////////////////////////////////////////////////
    //  Factory methods for stock shaders

    /**
     *  Call this to create a new "empty" shader, that will not draw anything.
     */
    static SkShader* CreateEmptyShader();

    /**
     *  Call this to create a new shader that just draws the specified color. This should always
     *  draw the same as a paint with this color (and no shader).
     */
    static SkShader* CreateColorShader(SkColor);

    /** Call this to create a new shader that will draw with the specified bitmap.
     *
     *  If the bitmap cannot be used (e.g. has no pixels, or its dimensions
     *  exceed implementation limits (currently at 64K - 1)) then SkEmptyShader
     *  may be returned.
     *
     *  If the src is kA8_Config then that mask will be colorized using the color on
     *  the paint.
     *
     *  @param src  The bitmap to use inside the shader
     *  @param tmx  The tiling mode to use when sampling the bitmap in the x-direction.
     *  @param tmy  The tiling mode to use when sampling the bitmap in the y-direction.
     *  @return     Returns a new shader object. Note: this function never returns null.
    */
    static SkShader* CreateBitmapShader(const SkBitmap& src,
                                        TileMode tmx, TileMode tmy,
                                        const SkMatrix* localMatrix = NULL);

    // NOTE: You can create an SkImage Shader with SkImage::newShader().

    /** Call this to create a new shader that will draw with the specified picture.
     *
     *  @param src  The picture to use inside the shader (if not NULL, its ref count
     *              is incremented). The SkPicture must not be changed after
     *              successfully creating a picture shader.
     *  @param tmx  The tiling mode to use when sampling the bitmap in the x-direction.
     *  @param tmy  The tiling mode to use when sampling the bitmap in the y-direction.
     *  @param tile The tile rectangle in picture coordinates: this represents the subset
     *              (or superset) of the picture used when building a tile. It is not
     *              affected by localMatrix and does not imply scaling (only translation
     *              and cropping). If null, the tile rect is considered equal to the picture
     *              bounds.
     *  @return     Returns a new shader object. Note: this function never returns null.
    */
    static SkShader* CreatePictureShader(const SkPicture* src,
                                         TileMode tmx, TileMode tmy,
                                         const SkMatrix* localMatrix,
                                         const SkRect* tile);

    /**
     *  Return a shader that will apply the specified localMatrix to the proxy shader.
     *  The specified matrix will be applied before any matrix associated with the proxy.
     *
     *  Note: ownership of the proxy is not transferred (though a ref is taken).
     */
    static SkShader* CreateLocalMatrixShader(SkShader* proxy, const SkMatrix& localMatrix);

    /**
     *  If this shader can be represented by another shader + a localMatrix, return that shader
     *  and, if not NULL, the localMatrix. If not, return NULL and ignore the localMatrix parameter.
     *
     *  Note: the returned shader (if not NULL) will have been ref'd, and it is the responsibility
     *  of the caller to balance that with unref() when they are done.
     */
    virtual SkShader* refAsALocalMatrixShader(SkMatrix* localMatrix) const;

    SK_TO_STRING_VIRT()
    SK_DEFINE_FLATTENABLE_TYPE(SkShader)

protected:
    void flatten(SkWriteBuffer&) const override;

    bool computeTotalInverse(const ContextRec&, SkMatrix* totalInverse) const;

    /**
     *  Your subclass must also override contextSize() if it overrides onCreateContext().
     *  Base class impl returns NULL.
     */
    virtual Context* onCreateContext(const ContextRec&, void* storage) const;

    virtual bool onAsLuminanceColor(SkColor*) const {
        return false;
    }

    virtual bool onIsABitmap(SkBitmap*, SkMatrix*, TileMode[2]) const {
        return false;
    }

private:
    // This is essentially const, but not officially so it can be modified in
    // constructors.
    SkMatrix fLocalMatrix;

    // So the SkLocalMatrixShader can whack fLocalMatrix in its SkReadBuffer constructor.
    friend class SkLocalMatrixShader;

    typedef SkFlattenable INHERITED;
};

#endif