src/gpu/text/GrTextUtils.h

/*
 * Copyright 2015 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef GrTextUtils_DEFINED
#define GrTextUtils_DEFINED

#include "GrColor.h"
#include "SkColorFilter.h"
#include "SkGr.h"
#include "SkPaint.h"
#include "SkScalar.h"
#include "SkTLazy.h"

class GrAtlasGlyphCache;
class GrAtlasTextBlob;
class GrAtlasTextStrike;
class GrClip;
class GrColorSpaceXform;
class GrContext;
class GrPaint;
class GrRenderTargetContext;
class GrShaderCaps;
class SkColorSpace;
class SkDrawFilter;
class SkGlyph;
class SkMatrix;
struct SkIRect;
struct SkPoint;
class SkGlyphCache;
class SkTextBlobRunIterator;
class SkSurfaceProps;

/**
 * A class to house a bunch of common text utilities.  This class should *ONLY* have static
 * functions.  It is not a namespace only because we wish to friend SkPaint
 */
class GrTextUtils {
public:
    /**
     *  This is used to wrap a SkPaint and its post-color filter color. It is also used by RunPaint
     *  (below). This keeps a pointer to the SkPaint it is initialized with and expects it to remain
     *  const. It is also used to transform to GrPaint.
     */
    class Paint {
    public:
        explicit Paint(const SkPaint* paint,
                       SkColorSpace* dstColorSpace,
                       GrColorSpaceXform* colorXformFromSRGB)
                : fPaint(paint)
                , fDstColorSpace(dstColorSpace)
                , fColorXformFromSRGB(colorXformFromSRGB) {
            this->initFilteredColor();
        }

        // These expose the paint's color run through its color filter (if any). This is only valid
        // when drawing grayscale/lcd glyph masks and not when drawing color glyphs.
        GrColor filteredPremulColor() const { return fFilteredPremulColor; }
        GrColor filteredUnpremulColor() const { return fFilteredUnpremulColor; }

        const SkPaint& skPaint() const { return *fPaint; }
        operator const SkPaint&() const { return this->skPaint(); }

        bool toGrPaint(GrMaskFormat, GrRenderTargetContext*, const SkMatrix& viewMatrix,
                       GrPaint*) const;

        // Just for RunPaint's constructor
        SkColorSpace* dstColorSpace() const { return fDstColorSpace; }
        GrColorSpaceXform* colorXformFromSRGB() const { return fColorXformFromSRGB; }

    protected:
        void initFilteredColor();
        Paint() = default;
        const SkPaint* fPaint;
        SkColorSpace* fDstColorSpace;
        GrColorSpaceXform* fColorXformFromSRGB;
        // This is the paint's color run through its color filter, if present. This color should
        // be used except when rendering bitmap text, in which case the bitmap must be filtered in
        // the fragment shader.
        GrColor fFilteredUnpremulColor;
        GrColor fFilteredPremulColor;
    };

    /**
     *  An extension of Paint that incorporated per-run modifications to the paint text settings and
     *  application of a draw filter. It expects its constructor arguments to remain alive and const
     *  during its lifetime.
     */
    class RunPaint : public Paint {
    public:
        RunPaint(const Paint* paint, SkDrawFilter* filter, const SkSurfaceProps& props)
                : fOriginalPaint(paint), fFilter(filter), fProps(props) {
            // Initially we represent the original paint.
            fPaint = &fOriginalPaint->skPaint();
            fDstColorSpace = fOriginalPaint->dstColorSpace();
            fColorXformFromSRGB = fOriginalPaint->colorXformFromSRGB();
            fFilteredPremulColor = fOriginalPaint->filteredPremulColor();
            fFilteredUnpremulColor = fOriginalPaint->filteredUnpremulColor();
        }

        bool modifyForRun(const SkTextBlobRunIterator&);

    private:
        SkTLazy<SkPaint> fModifiedPaint;
        const Paint* fOriginalPaint;
        SkDrawFilter* fFilter;
        const SkSurfaceProps& fProps;
    };

    // Functions for appending BMP text to GrAtlasTextBlob
    static void DrawBmpText(GrAtlasTextBlob*, int runIndex, GrAtlasGlyphCache*,
                            const SkSurfaceProps&, const Paint& paint, uint32_t scalerContextFlags,
                            const SkMatrix& viewMatrix, const char text[], size_t byteLength,
                            SkScalar x, SkScalar y);

    static void DrawBmpPosText(GrAtlasTextBlob*, int runIndex, GrAtlasGlyphCache*,
                               const SkSurfaceProps&, const Paint& paint,
                               uint32_t scalerContextFlags, const SkMatrix& viewMatrix,
                               const char text[], size_t byteLength, const SkScalar pos[],
                               int scalarsPerPosition, const SkPoint& offset);

    // functions for appending distance field text
    static bool CanDrawAsDistanceFields(const SkPaint& skPaint, const SkMatrix& viewMatrix,
                                        const SkSurfaceProps& props, const GrShaderCaps& caps);

    static void DrawDFText(GrAtlasTextBlob* blob, int runIndex, GrAtlasGlyphCache*,
                           const SkSurfaceProps&, const Paint& paint, uint32_t scalerContextFlags,
                           const SkMatrix& viewMatrix, const char text[], size_t byteLength,
                           SkScalar x, SkScalar y);

    static void DrawDFPosText(GrAtlasTextBlob* blob, int runIndex, GrAtlasGlyphCache*,
                              const SkSurfaceProps&, const Paint& paint,
                              uint32_t scalerContextFlags, const SkMatrix& viewMatrix,
                              const char text[], size_t byteLength, const SkScalar pos[],
                              int scalarsPerPosition, const SkPoint& offset);

    // Functions for drawing text as paths
    static void DrawTextAsPath(GrContext*, GrRenderTargetContext*, const GrClip& clip,
                               const SkPaint& paint, const SkMatrix& viewMatrix, const char text[],
                               size_t byteLength, SkScalar x, SkScalar y,
                               const SkIRect& clipBounds);

    static void DrawPosTextAsPath(GrContext* context, GrRenderTargetContext* rtc,
                                  const SkSurfaceProps& props, const GrClip& clip,
                                  const SkPaint& paint, const SkMatrix& viewMatrix,
                                  const char text[], size_t byteLength, const SkScalar pos[],
                                  int scalarsPerPosition, const SkPoint& offset,
                                  const SkIRect& clipBounds);

    static bool ShouldDisableLCD(const SkPaint& paint);


private:
    static uint32_t FilterTextFlags(const SkSurfaceProps& surfaceProps, const SkPaint& paint);

    static void InitDistanceFieldPaint(GrAtlasTextBlob* blob,
                                       SkPaint* skPaint,
                                       SkScalar* textRatio,
                                       const SkMatrix& viewMatrix);

    static void BmpAppendGlyph(GrAtlasTextBlob*, int runIndex, GrAtlasGlyphCache*,
                               GrAtlasTextStrike**, const SkGlyph&, int left, int top,
                               GrColor color, SkGlyphCache*);

    static bool DfAppendGlyph(GrAtlasTextBlob*, int runIndex, GrAtlasGlyphCache*,
                              GrAtlasTextStrike**, const SkGlyph&,
                              SkScalar sx, SkScalar sy, GrColor color,
                              SkGlyphCache* cache,
                              SkScalar textRatio, const SkMatrix& viewMatrix);
};

#endif