Use texture barriers to read directly from the RT

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"
 
@@ skipping 14 matching lines @@
 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);
 }
 
+bool GrXferProcessor::willNeedXferBarrier(const GrRenderTarget* rt,
+                                          const GrDrawTargetCaps& caps,
+                                          GrXferBarrierType* outBarrierType) const {
+    if (static_cast<const GrSurface*>(rt) == this->getDstCopyTexture()) {
+        // Texture barriers are required when a shader reads and renders to the same texture.
+        SkASSERT(rt);
+        SkASSERT(caps.textureBarrierSupport());
+        *outBarrierType = kTexture_GrXferBarrierType;
+        return true;
+    }
+    return false;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 GrXferProcessor* GrXPFactory::createXferProcessor(const GrProcOptInfo& colorPOI,
                                                   const GrProcOptInfo& coveragePOI,
                                                   const GrDeviceCoordTexture* dstCopy,
                                                   const GrDrawTargetCaps& caps) const {
 #ifdef SK_DEBUG
     if (this->willReadDstColor(caps, colorPOI, coveragePOI)) {
         if (!caps.dstReadInShaderSupport()) {
             SkASSERT(dstCopy && dstCopy->texture());
         } else {
             SkASSERT(!dstCopy || !dstCopy->texture()); 
         }
     } else {
         SkASSERT(!dstCopy || !dstCopy->texture()); 
     }
 #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.dstReadInShaderSupport());
 }