Add XP to handle the cases where we disable color write.

include/gpu/GrXferProcessor.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 GrXferProcessor_DEFINED
 #define GrXferProcessor_DEFINED
 
@@ skipping 68 matching lines @@
 
     /**
      * Determines which optimizations (as described by the ptFlags above) can be performed by
      * the draw with this xfer processor. If this function is called, the xfer processor may change
      * its state to reflected the given blend optimizations. If the XP needs to see a specific input
      * color to blend correctly, it will set the OverrideColor flag and the output parameter
      * overrideColor will be the required value that should be passed into the XP. 
      * A caller who calls this function on a XP is required to honor the returned OptFlags
      * and color values for its draw.
      */
-    // TODO: remove need for colorWriteDisabled once colorWriteDisabled is its own XP.
     virtual OptFlags getOptimizations(const GrProcOptInfo& colorPOI,
                                       const GrProcOptInfo& coveragePOI,
-                                      bool colorWriteDisabled,
                                       bool doesStencilWrite,
                                       GrColor* overrideColor,
                                       const GrDrawTargetCaps& caps) = 0;
 
     struct BlendInfo {
+        BlendInfo() : fWriteColor(true) {}
+
         GrBlendCoeff fSrcBlend;
         GrBlendCoeff fDstBlend;
         GrColor      fBlendConstant;
+        bool         fWriteColor;
     };
 
     virtual void getBlendInfo(BlendInfo* blendInfo) const = 0;
 
     /** Will this prceossor read the destination pixel value? */
     bool willReadDstColor() const { return fWillReadDstColor; }
 
     /** 
      * Returns whether or not this xferProcossor will set a secondary output to be used with dual
      * source blending.
@@ skipping 58 matching lines @@
     virtual bool supportsRGBCoverage(GrColor knownColor, uint32_t knownColorFlags) const = 0;
 
     /**
      * Depending on color blend mode requested it may or may not be possible to correctly blend with
      * fractional pixel coverage generated by the fragment shader.
      *
      * This function considers the known color and coverage input into the xfer processor and
      * certain state information (colorWriteDisabled) to determine whether
      * coverage can be handled correctly.
      */
-    // TODO: remove need for colorWriteDisabled once colorWriteDisabled is its own XP.
-    virtual bool canApplyCoverage(const GrProcOptInfo& colorPOI, const GrProcOptInfo& coveragePOI,
-                                  bool colorWriteDisabled) const = 0;
+    virtual bool canApplyCoverage(const GrProcOptInfo& colorPOI,
+                                  const GrProcOptInfo& coveragePOI) const = 0;
 
 
     struct InvariantOutput {
         bool        fWillBlendWithDst;
         GrColor     fBlendedColor;
         uint32_t    fBlendedColorFlags;
     };
 
     /** 
      * This function returns known information about the output of the xfer processor produced by
      * this xp factory. The invariant color information returned by this function refers to the
      * final color produced after all blending.
      */
-    // TODO: remove need for colorWriteDisabled once only XP can read dst.
     virtual void getInvariantOutput(const GrProcOptInfo& colorPOI, const GrProcOptInfo& coveragePOI,
-                                    bool colorWriteDisabled, InvariantOutput*) const = 0;
+                                    InvariantOutput*) const = 0;
 
     /**
      * Determines whether multiplying the computed per-pixel color by the pixel's fractional
      * coverage before the blend will give the correct final destination color. In general it
      * will not as coverage is applied after blending.
      */
     virtual bool canTweakAlphaForCoverage() const = 0;
 
+    /**
+     *  Returns true if the XP generated by this factory will read dst.
+     */
+    // TODO: Currently this function must also check if the color/coverage stages read dst.
+    //       Once only XP's can read dst we can remove the ProcOptInfo's from this function.
+    virtual bool willReadDst(const GrProcOptInfo& colorPOI,
+                             const GrProcOptInfo& coveragePOI) const = 0;
+
     bool isEqual(const GrXPFactory& that) const {
         if (this->classID() != that.classID()) {
             return false;
         }
         return this->onIsEqual(that);
     }
 
     /**
       * Helper for down-casting to a GrXPFactory subclass
       */
@@ skipping 29 matching lines @@
     enum {
         kIllegalXPFClassID = 0,
     };
     static int32_t gCurrXPFClassID;
 
     typedef GrProgramElement INHERITED;
 };
 
 #endif