Exact Ganesh Gradients for Special Cases

src/effects/gradients/SkGradientShaderPriv.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkGradientShaderPriv_DEFINED
 #define SkGradientShaderPriv_DEFINED
 
 #include "SkGradientBitmapCache.h"
 #include "SkGradientShader.h"
 #include "SkClampRange.h"
 #include "SkColorPriv.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
 #include "SkMallocPixelRef.h"
 #include "SkUtils.h"
 #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) {
         if (v0 == v1) {
             sk_memset32(dst, v0, count);
         } else {
             int pairs = count >> 1;
             for (int i = 0; i < pairs; i++) {
                 *dst++ = v0;
                 *dst++ = v1;
@@ skipping 158 matching lines @@
         kCache32Count   = (1 << kCache32Bits),
         kCache32Shift   = 16 - kCache32Bits,
         kSqrt32Shift    = 8 - kCache32Bits,
 
         /// This value is used to *read* the dither cache; it may be 0
         /// if dithering is disabled.
         kDitherStride32 = kCache32Count,
         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:
     class GradientShaderBase4fContext;
 
     SkGradientShaderBase(SkReadBuffer& );
     void flatten(SkWriteBuffer&) const override;
     SK_TO_STRING_OVERRIDE()
 
     const SkMatrix fPtsToUnit;
     TileMode    fTileMode;
     TileProc    fTileProc;
-    int         fColorCount;
     uint8_t     fGradFlags;
 
     struct Rec {
         SkFixed     fPos;   // 0...1
         uint32_t    fScale; // (1 << 24) / range
     };
     Rec*        fRecs;
 
     void commonAsAGradient(GradientInfo*, bool flipGrad = false) const;
 
@@ skipping 13 matching lines @@
 private:
     enum {
         kColorStorageCount = 4, // more than this many colors, and we'll use sk_malloc for the space
 
         kStorageSize = kColorStorageCount * (sizeof(SkColor) + sizeof(SkScalar) + sizeof(Rec))
     };
     SkColor     fStorage[(kStorageSize + 3) >> 2];
 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;
 
     GradientShaderCache* refCache(U8CPU alpha, bool dither) const;
     mutable SkMutex                           fCacheMutex;
     mutable SkAutoTUnref<GradientShaderCache> fCache;
 
     void initCommon();
 
     typedef SkShader INHERITED;
@@ skipping 59 matching lines @@
     class GLSLProcessor;
 
     GrGradientEffect(GrContext* ctx,
                      const SkGradientShaderBase& shader,
                      const SkMatrix& matrix,
                      SkShader::TileMode tileMode);
 
     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,
         kAfterInterp_PremulType,
     };
 
     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];
     }
 
 protected:
     /** Populates a pair of arrays with colors and stop info to construct a random gradient.
         The function decides whether stop values should be used or not. The return value indicates
         the number of colors, which will be capped by kMaxRandomGradientColors. colors should be
         sized to be at least kMaxRandomGradientColors. stops is a pointer to an array of at least
         size kMaxRandomGradientColors. It may be updated to nullptr, indicating that nullptr should be
         passed to the gradient factory rather than the array.
     */
     static const int kMaxRandomGradientColors = 4;
     static int RandomGradientParams(SkRandom* r,
                                     SkColor colors[kMaxRandomGradientColors],
                                     SkScalar** stops,
                                     SkShader::TileMode* tm);
 
     bool onIsEqual(const GrFragmentProcessor&) const override;
 
     void onComputeInvariantOutput(GrInvariantOutput* inout) const override;
 
     const GrCoordTransform& getCoordTransform() const { return fCoordTransform; }
 
 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;
 
 protected:
     /**
      * Subclasses must call this. It will return a key for the part of the shader code controlled
      * by the base class. The subclasses must stick it in their key and then pass it to the below
      * emit* functions from their emitCode function.
      */
     static uint32_t GenBaseGradientKey(const GrProcessor&);
 
     // Emits the uniform used as the y-coord to texture samples in derived classes. Subclasses
     // 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,
                    const GrGradientEffect&,
                    const char* gradientTValue,
                    const char* outputColor,
                    const char* inputColor,
                    const SamplerHandle* texSamplers);
 
 private:
     enum {
         // 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;
 };
 
 #endif
 
 #endif