Add mixed samples support to XPs

src/gpu/gl/GrGLXferProcessor.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gl/GrGLXferProcessor.h"
 
 #include "GrXferProcessor.h"
@@ skipping 45 matching lines @@
 
         fsBuilder->codeAppendf("vec4 %s = ", dstColor);
         fsBuilder->appendTextureLookup(args.fSamplers[0], "_dstTexCoord", kVec2f_GrSLType);
         fsBuilder->codeAppend(";");
     }
 
     this->emitBlendCodeForDstRead(args.fPB, args.fInputColor, dstColor, args.fOutputPrimary,
                                   args.fXP);
 
     // Apply coverage.
-    if (args.fXP.readsCoverage()) {
+    if (args.fXP.dstReadUsesMixedSamples()) {
+        if (args.fXP.readsCoverage()) {
+            fsBuilder->codeAppendf("%s *= %s;", args.fOutputPrimary, args.fInputCoverage);
+            fsBuilder->codeAppendf("%s = %s;", args.fOutputSecondary, args.fInputCoverage);
+        } else {
+            fsBuilder->codeAppendf("%s = vec4(1.0);", args.fOutputSecondary);
+        }
+    } else if (args.fXP.readsCoverage()) {
         fsBuilder->codeAppendf("%s = %s * %s + (vec4(1.0) - %s) * %s;",
                                args.fOutputPrimary, args.fInputCoverage,
                                args.fOutputPrimary, args.fInputCoverage, dstColor);
     }
 }
 
 void GrGLXferProcessor::setData(const GrGLProgramDataManager& pdm, const GrXferProcessor& xp) {
     if (xp.getDstTexture()) {
         if (fDstTopLeftUni.isValid()) {
             pdm.set2f(fDstTopLeftUni, static_cast<GrGLfloat>(xp.dstTextureOffset().fX),
                       static_cast<GrGLfloat>(xp.dstTextureOffset().fY));
             pdm.set2f(fDstScaleUni, 1.f / xp.getDstTexture()->width(),
                       1.f / xp.getDstTexture()->height());
         } else {
             SkASSERT(!fDstScaleUni.isValid());
         }
     } else {
         SkASSERT(!fDstTopLeftUni.isValid());
         SkASSERT(!fDstScaleUni.isValid());
     }
     this->onSetData(pdm, xp);
 }