Exact Ganesh Gradients for Special Cases

src/effects/gradients/SkGradientShaderPriv.h

Index: src/effects/gradients/SkGradientShaderPriv.h
diff --git a/src/effects/gradients/SkGradientShaderPriv.h b/src/effects/gradients/SkGradientShaderPriv.h
index 50ad427e4ae1d5f3aa03f37b79e496d930be5b52..496b603db18cb4d01d77b347564970c1cd5888ec 100644
--- a/src/effects/gradients/SkGradientShaderPriv.h
+++ b/src/effects/gradients/SkGradientShaderPriv.h
@@ -19,6 +19,8 @@
 #include "SkShader.h"
 #include "SkOnce.h"
 
+#define GR_GL_USE_ACCURATE_HARD_STOP_GRADIENTS 1
+
 static inline void sk_memset32_dither(uint32_t dst[], uint32_t v0, uint32_t v1,
                                int count) {
     if (count > 0) {
@@ -197,17 +199,6 @@ public:
         kDitherStride16 = kCache16Count,
     };
 
-    enum GpuColorType {
-        kTwo_GpuColorType,
-        kThree_GpuColorType, // Symmetric three color
-        kTexture_GpuColorType
-    };
-
-    // Determines and returns the gradient is a two color gradient, symmetric three color gradient
-    // or other (texture gradient). If it is two or symmetric three color, the colors array will
-    // also be filled with the gradient colors
-    GpuColorType getGpuColorType(SkColor colors[3]) const;
-
     uint32_t getGradFlags() const { return fGradFlags; }
 
 protected:
@@ -220,7 +211,6 @@ protected:
     const SkMatrix fPtsToUnit;
     TileMode    fTileMode;
     TileProc    fTileProc;
-    int         fColorCount;
     uint8_t     fGradFlags;
 
     struct Rec {
@@ -254,9 +244,15 @@ private:
 public:
     SkColor*    fOrigColors; // original colors, before modulation by paint in context.
     SkScalar*   fOrigPos;   // original positions
+    int         fColorCount;
+
+    SkTArray<sk_sp<SkShader>> fSubGradients;
 
     bool colorsAreOpaque() const { return fColorsAreOpaque; }
 
+    TileMode getTileMode() const { return fTileMode; }
+    Rec* getRecs() const { return fRecs; }
+
 private:
     bool        fColorsAreOpaque;
 
@@ -336,9 +332,30 @@ public:
     virtual ~GrGradientEffect();
 
     bool useAtlas() const { return SkToBool(-1 != fRow); }
-    SkScalar getYCoord() const { return fYCoord; };
+    SkScalar getYCoord() const { return fYCoord; }
 
-    SkGradientShaderBase::GpuColorType getColorType() const { return fColorType; }
+    enum ColorType {
+        kTwo_ColorType,
+        kThree_ColorType, // Symmetric three color
+        kTexture_ColorType,
+
+#if GR_GL_USE_ACCURATE_HARD_STOP_GRADIENTS
+        kHardStopCentered_ColorType,   // 0, 0.5, 0.5, 1
+        kHardStopLeftEdged_ColorType,  // 0, 0, 1
+        kHardStopRightEdged_ColorType, // 0, 1, 1
+#endif
+    };
+
+    ColorType getColorType() const { return fColorType; }
+
+    // Determines the type of gradient, one of:
+    //    - Two-color
+    //    - Symmetric three-color
+    //    - Texture
+    //    - Centered hard stop
+    //    - Left-edged hard stop
+    //    - Right-edged hard stop
+    ColorType determineColorTypeAndNumHardStops(const SkGradientShaderBase& shader);
 
     enum PremulType {
         kBeforeInterp_PremulType,
@@ -348,8 +365,8 @@ public:
     PremulType getPremulType() const { return fPremulType; }
 
     const SkColor* getColors(int pos) const {
-        SkASSERT(fColorType != SkGradientShaderBase::kTexture_GpuColorType);
-        SkASSERT((pos-1) <= fColorType);
+        SkASSERT(fColorType != kTexture_ColorType);
+        SkASSERT(pos < fColors.count());
         return &fColors[pos];
     }
 
@@ -376,26 +393,31 @@ protected:
 private:
     static const GrCoordSet kCoordSet = kLocal_GrCoordSet;
 
+    SkTDArray<SkColor>  fColors;
+    SkTDArray<SkScalar> fPositions;
+    SkShader::TileMode  fTileMode;
+
     GrCoordTransform fCoordTransform;
     GrTextureAccess fTextureAccess;
     SkScalar fYCoord;
     GrTextureStripAtlas* fAtlas;
     int fRow;
     bool fIsOpaque;
-    SkGradientShaderBase::GpuColorType fColorType;
-    SkColor fColors[3]; // More than 3 colors we use texture
-    PremulType fPremulType; // This only changes behavior for two and three color special cases.
-                            // It is already baked into to the table for texture gradients.
+    ColorType fColorType;
+    PremulType fPremulType; // This is already baked into the table for texture gradients, and
+                            // only changes behavior for gradients that don't use a texture.
     typedef GrFragmentProcessor INHERITED;
 
 };
 
 ///////////////////////////////////////////////////////////////////////////////
 
-// Base class for GLSL gradient effects
+// Base class for GL gradient effects
 class GrGradientEffect::GLSLProcessor : public GrGLSLFragmentProcessor {
 public:
-    GLSLProcessor();
+    GLSLProcessor() {
+        fCachedYCoord = SK_ScalarMax;
+    }
 
 protected:
     void onSetData(const GrGLSLProgramDataManager&, const GrProcessor&) override;
@@ -412,10 +434,10 @@ protected:
     // should call this method from their emitCode().
     void emitUniforms(GrGLSLUniformHandler*, const GrGradientEffect&);
 
-
-    // emit code that gets a fragment's color from an expression for t; Has branches for 3 separate
-    // control flows inside -- 2 color gradients, 3 color symmetric gradients (both using
-    // native GLSL mix), and 4+ color gradients that use the traditional texture lookup.
+    // Emit code that gets a fragment's color from an expression for t; has branches for
+    // several control flows inside -- 2-color gradients, 3-color symmetric gradients, 4+
+    // color gradients that use the traditional texture lookup, as well as several varieties
+    // of hard stop gradients
     void emitColor(GrGLSLFPFragmentBuilder* fragBuilder,
                    GrGLSLUniformHandler* uniformHandler,
                    const GrGLSLCaps* caps,
@@ -430,16 +452,28 @@ private:
         // First bit for premul before/after interp
         kPremulBeforeInterpKey = 1,
 
-        // Next two bits for 2/3 color type (neither means using texture atlas)
-        kTwoColorKey   = 4,
-        kThreeColorKey = 6,
+        // Next three bits for 2/3 color type or different special
+        // hard stop cases (neither means using texture atlas)
+        kTwoColorKey            =  2,
+        kThreeColorKey          =  4,
+#if GR_GL_USE_ACCURATE_HARD_STOP_GRADIENTS
+        kHardStopCenteredKey    =  6,
+        kHardStopZeroZeroOneKey =  8,
+        kHardStopZeroOneOneKey  = 10,
+
+        // Next two bits for tile mode
+        kClampTileMode  = 16,

[bsalomon, 2016/08/10 14:33:20]

Can you preserve the alignment of the values?

+        kRepeatTileMode = 32,
+        kMirrorTileMode = 48,
+
+        // Lower six bits for premul, 2/3 color type, and tile mode
+        kReservedBits = 6,
+#endif
     };
 
     SkScalar fCachedYCoord;
+    GrGLSLProgramDataManager::UniformHandle fColorsUni;
     GrGLSLProgramDataManager::UniformHandle fFSYUni;
-    GrGLSLProgramDataManager::UniformHandle fColorStartUni;
-    GrGLSLProgramDataManager::UniformHandle fColorMidUni;
-    GrGLSLProgramDataManager::UniformHandle fColorEndUni;
 
     typedef GrGLSLFragmentProcessor INHERITED;
 };