Implement support for KHR_blend_equation_advanced

src/gpu/gl/builders/GrGLFragmentShaderBuilder.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrGLFragmentShaderBuilder_DEFINED
 #define GrGLFragmentShaderBuilder_DEFINED
 
@@ skipping 48 matching lines @@
  * just call it FPShaderBuilder
  */
 class GrGLXPFragmentBuilder : public GrGLFragmentBuilder {
 public:
     GrGLXPFragmentBuilder(GrGLProgramBuilder* program) : INHERITED(program) {}
 
     /** Returns the variable name that holds the color of the destination pixel. This may be NULL if
         no effect advertised that it will read the destination. */
     virtual const char* dstColor() = 0;
 
+    /** Adds any necessary layout qualifiers in order to legalize the supplied blend equation with
+        this shader. It is only legal to call this method with an advanced blend equation, and only
+        if these equations are supported. */
+    virtual void enableAdvancedBlendEquationIfNeeded(GrBlendEquation) = 0;
+
 private:
     typedef GrGLFragmentBuilder INHERITED;
 };
 
 // TODO rename to Fragment Builder
 class GrGLFragmentShaderBuilder : public GrGLXPFragmentBuilder {
 public:
     typedef uint8_t DstReadKey;
     typedef uint8_t FragPosKey;
 
     /**  Returns a key for adding code to read the copy-of-dst color in service of effects that
         require reading the dst. It must not return 0 because 0 indicates that there is no dst
         copy read at all (in which case this function should not be called). */
     static DstReadKey KeyForDstRead(const GrTexture* dstCopy, const GrGLCaps&);
 
     /** Returns a key for reading the fragment location. This should only be called if there is an
        effect that will requires the fragment position. If the fragment position is not required,
        the key is 0. */
     static FragPosKey KeyForFragmentPosition(const GrRenderTarget* dst, const GrGLCaps&);
 
     GrGLFragmentShaderBuilder(GrGLProgramBuilder* program, uint8_t fragPosKey);
 
     // true public interface, defined explicitly in the abstract interfaces above
     bool enableFeature(GLSLFeature) override;
     virtual SkString ensureFSCoords2D(const GrGLProcessor::TransformedCoordsArray& coords,
                                       int index) override;
     const char* fragmentPosition() override;
     const char* dstColor() override;
 
+    void enableAdvancedBlendEquationIfNeeded(GrBlendEquation) override;
+
 private:
     // Private public interface, used by GrGLProgramBuilder to build a fragment shader
     void enableCustomOutput();
     void enableSecondaryOutput();
     const char* getPrimaryColorOutputName() const;
     const char* getSecondaryColorOutputName() const;
     bool compileAndAttachShaders(GrGLuint programId, SkTDArray<GrGLuint>* shaderIds);
     void bindFragmentShaderLocations(GrGLuint programID);
 
     // As GLProcessors emit code, there are some conditions we need to verify.  We use the below
     // state to track this.  The reset call is called per processor emitted.
     bool hasReadDstColor() const { return fHasReadDstColor; }
     bool hasReadFragmentPosition() const { return fHasReadFragmentPosition; }
     void reset() {
         fHasReadDstColor = false;
         fHasReadFragmentPosition = false;
     }
 
     /*
      * An internal call for GrGLProgramBuilder to use to add varyings to the vertex shader
      */
     void addVarying(GrGLVarying*, GrSLPrecision);
 
     /**
      * Features that should only be enabled by GrGLFragmentShaderBuilder itself.
      */
     enum GLSLPrivateFeature {
         kFragCoordConventions_GLSLPrivateFeature = kLastGLSLFeature + 1,
-        kLastGLSLPrivateFeature = kFragCoordConventions_GLSLPrivateFeature
+        kBlendEquationAdvanced_GLSLPrivateFeature,
+        kLastGLSLPrivateFeature = kBlendEquationAdvanced_GLSLPrivateFeature
     };
 
     // Interpretation of DstReadKey when generating code
     enum {
         kNoDstRead_DstReadKey           = 0,
         kYesDstRead_DstReadKeyBit       = 0x1, // Set if we do a dst-copy-read.
         kUseAlphaConfig_DstReadKeyBit   = 0x2, // Set if dst-copy config is alpha only.
         kTopLeftOrigin_DstReadKeyBit    = 0x4, // Set if dst-copy origin is top-left.
     };
 
@@ skipping 16 matching lines @@
     // the program creator
     bool fHasReadDstColor;
     bool fHasReadFragmentPosition;
 
     friend class GrGLProgramBuilder;
 
     typedef GrGLXPFragmentBuilder INHERITED;
 };
 
 #endif