Perform coverage blend with the dst in the shader when using a dst-reading xfermode.

src/gpu/gl/GrGLProgramDesc.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrGLProgramDesc.h"
 #include "GrBackendEffectFactory.h"
 #include "GrDrawEffect.h"
@@ skipping 85 matching lines @@
     }
 
     if (readsDst) {
         GrAssert(NULL != dstCopy);
         desc->fDstRead = GrGLShaderBuilder::KeyForDstRead(dstCopy->texture(), gpu->glCaps());
         GrAssert(0 != desc->fDstRead);
     } else {
         desc->fDstRead = 0;
     }
 
-    desc->fDualSrcOutput = kNone_DualSrcOutput;
+    desc->fCoverageOutput = kModulate_CoverageOutput;
 
     // Currently the experimental GS will only work with triangle prims (and it doesn't do anything
     // other than pass through values from the VS to the FS anyway).
 #if GR_GL_EXPERIMENTAL_GS
 #if 0
     desc->fExperimentalGS = gpu->caps().geometryShaderSupport();
 #else
     desc->fExperimentalGS = false;
 #endif
 #endif
@@ skipping 27 matching lines @@
         if (drawState.getStencil().doesWrite()) {
             desc->fDiscardIfZeroCoverage = true;
             desc->fFirstCoverageStage = firstCoverageStage;
         }
 
         if (gpu->caps()->dualSourceBlendingSupport() &&
             !(blendOpts & (GrDrawState::kEmitCoverage_BlendOptFlag |
                            GrDrawState::kCoverageAsAlpha_BlendOptFlag))) {
             if (kZero_GrBlendCoeff == dstCoeff) {
                 // write the coverage value to second color
-                desc->fDualSrcOutput =  kCoverage_DualSrcOutput;
+                desc->fCoverageOutput =  kSecondaryCoverage_CoverageOutput;
                 desc->fFirstCoverageStage = firstCoverageStage;
             } else if (kSA_GrBlendCoeff == dstCoeff) {
                 // SA dst coeff becomes 1-(1-SA)*coverage when dst is partially covered.
-                desc->fDualSrcOutput = kCoverageISA_DualSrcOutput;
+                desc->fCoverageOutput = kSecondaryCoverageISA_CoverageOutput;
                 desc->fFirstCoverageStage = firstCoverageStage;
             } else if (kSC_GrBlendCoeff == dstCoeff) {
                 // SA dst coeff becomes 1-(1-SA)*coverage when dst is partially covered.
-                desc->fDualSrcOutput = kCoverageISC_DualSrcOutput;
+                desc->fCoverageOutput = kSecondaryCoverageISC_CoverageOutput;
                 desc->fFirstCoverageStage = firstCoverageStage;
             }
+        } else if (readsDst &&
+                   kOne_GrBlendCoeff == drawState.getSrcBlendCoeff() &&
+                   kZero_GrBlendCoeff == drawState.getDstBlendCoeff()) {
+            desc->fCoverageOutput = kCombineWithDst_CoverageOutput;
+            desc->fFirstCoverageStage = firstCoverageStage;
         }
     }
 
     desc->fPositionAttributeIndex = drawState.positionAttributeIndex();
     desc->fLocalCoordAttributeIndex = drawState.localCoordAttributeIndex();
 
     // For constant color and coverage we need an attribute with an index beyond those already set
     int availableAttributeIndex = drawState.getVertexAttribCount();
     if (requiresColorAttrib) {
         desc->fColorAttributeIndex = drawState.colorVertexAttributeIndex();
     } else if (GrGLProgramDesc::kAttribute_ColorInput == desc->fColorInput) {
         GrAssert(availableAttributeIndex < GrDrawState::kMaxVertexAttribCnt);
         desc->fColorAttributeIndex = availableAttributeIndex;
         availableAttributeIndex++;
     } else {
         desc->fColorAttributeIndex = -1;
     }
 
     if (requiresCoverageAttrib) {
         desc->fCoverageAttributeIndex = drawState.coverageVertexAttributeIndex();
     } else if (GrGLProgramDesc::kAttribute_ColorInput == desc->fCoverageInput) {
         GrAssert(availableAttributeIndex < GrDrawState::kMaxVertexAttribCnt);
         desc->fCoverageAttributeIndex = availableAttributeIndex;
     } else {
         desc->fCoverageAttributeIndex = -1;
     }
 }