Only discard for XP dstCopies if we have a coverage value.

src/gpu/GrXferProcessor.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrXferProcessor.h"
 #include "gl/GrGLCaps.h"
 
-GrXferProcessor::GrXferProcessor() : fWillReadDstColor(false), fDstCopyTextureOffset() {
+GrXferProcessor::GrXferProcessor()
+    : fWillReadDstColor(false), fReadsCoverage(true), fDstCopyTextureOffset() {
 }
 
 GrXferProcessor::GrXferProcessor(const GrDeviceCoordTexture* dstCopy, bool willReadDstColor)
     : fWillReadDstColor(willReadDstColor)
+    , fReadsCoverage(true)
     , fDstCopyTextureOffset() {
     if (dstCopy && dstCopy->texture()) {
         fDstCopy.reset(dstCopy->texture());
         fDstCopyTextureOffset = dstCopy->offset();
         this->addTextureAccess(&fDstCopy);
         this->setWillReadFragmentPosition();
     }
 }
 
+GrXferProcessor::OptFlags GrXferProcessor::getOptimizations(const GrProcOptInfo& colorPOI,
+                                                            const GrProcOptInfo& coveragePOI,
+                                                            bool doesStencilWrite,
+                                                            GrColor* overrideColor,
+                                                            const GrDrawTargetCaps& caps) {
+    GrXferProcessor::OptFlags flags = this->onGetOptimizations(colorPOI,
+                                                               coveragePOI,
+                                                               doesStencilWrite,
+                                                               overrideColor,
+                                                               caps);
+
+    if (flags & GrXferProcessor::kIgnoreCoverage_OptFlag) {
+        fReadsCoverage = false;
+    }
+    return flags;
+}
+
 void GrXferProcessor::getGLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const {
     uint32_t key = this->willReadDstColor() ? 0x1 : 0x0;
     if (this->getDstCopyTexture() &&
         kTopLeft_GrSurfaceOrigin == this->getDstCopyTexture()->origin()) {
         key |= 0x2;
     }
     b->add32(key);
     this->onGetGLProcessorKey(caps, b);
 }
 
@@ skipping 29 matching lines @@
 #endif
     return this->onCreateXferProcessor(caps, colorPOI, coveragePOI, dstCopy);
 }
 
 bool GrXPFactory::willNeedDstCopy(const GrDrawTargetCaps& caps, const GrProcOptInfo& colorPOI,
                                   const GrProcOptInfo& coveragePOI) const {
     return (this->willReadDstColor(caps, colorPOI, coveragePOI) 
             && !caps.shaderCaps()->dstReadInShaderSupport());
 }