Prefer dual source/framebuffer fetch paths for GPU LCD.

src/gpu/effects/GrPorterDuffXferProcessor.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 "effects/GrPorterDuffXferProcessor.h"
 
 #include "GrBlend.h"
@@ skipping 713 matching lines @@
 
 GrXferProcessor*
 GrPorterDuffXPFactory::onCreateXferProcessor(const GrCaps& caps,
                                              const GrProcOptInfo& colorPOI,
                                              const GrProcOptInfo& covPOI,
                                              bool hasMixedSamples,
                                              const DstTexture* dstTexture) const {
     BlendFormula blendFormula;
     if (covPOI.isFourChannelOutput()) {
         if (SkXfermode::kSrcOver_Mode == fXfermode &&
-            kRGBA_GrColorComponentFlags == colorPOI.validFlags()) {
+            kRGBA_GrColorComponentFlags == colorPOI.validFlags() &&
+            !caps.shaderCaps()->dualSourceBlendingSupport() &&
+            !caps.shaderCaps()->dstReadInShaderSupport()) {
+            // If we don't have dual source blending or in shader dst reads, we fall back to this
+            // trick for rendering SrcOver LCD text instead of doing a dst copy.
             SkASSERT(!dstTexture || !dstTexture->texture());
             return PDLCDXferProcessor::Create(fXfermode, colorPOI);
         }
         blendFormula = get_lcd_blend_formula(covPOI, fXfermode);
     } else {
         blendFormula = get_blend_formula(colorPOI, covPOI, hasMixedSamples, fXfermode);
     }
 
     if (blendFormula.hasSecondaryOutput() && !caps.shaderCaps()->dualSourceBlendingSupport()) {
         return new ShaderPDXferProcessor(dstTexture, hasMixedSamples, fXfermode);
@@ skipping 40 matching lines @@
                                              bool hasMixedSamples) const {
     if (caps.shaderCaps()->dualSourceBlendingSupport()) {
         return false;
     }
     
     // When we have four channel coverage we always need to read the dst in order to correctly
     // blend. The one exception is when we are using srcover mode and we know the input color into
     // the XP.
     if (covPOI.isFourChannelOutput()) {
         if (SkXfermode::kSrcOver_Mode == fXfermode &&
-            kRGBA_GrColorComponentFlags == colorPOI.validFlags()) {
+            kRGBA_GrColorComponentFlags == colorPOI.validFlags() &&
+            !caps.shaderCaps()->dstReadInShaderSupport()) {
             return false;
         }
         return get_lcd_blend_formula(covPOI, fXfermode).hasSecondaryOutput();
     }
     // We fallback on the shader XP when the blend formula would use dual source blending but we
     // don't have support for it.
     return get_blend_formula(colorPOI, covPOI, hasMixedSamples, fXfermode).hasSecondaryOutput();
 }
 
 GR_DEFINE_XP_FACTORY_TEST(GrPorterDuffXPFactory);
 
 const GrXPFactory* GrPorterDuffXPFactory::TestCreate(GrProcessorTestData* d) {
     SkXfermode::Mode mode = SkXfermode::Mode(d->fRandom->nextULessThan(SkXfermode::kLastCoeffMode));
     return GrPorterDuffXPFactory::Create(mode);
 }
 
 void GrPorterDuffXPFactory::TestGetXPOutputTypes(const GrXferProcessor* xp,
                                                  int* outPrimary,
                                                  int* outSecondary) {
     if (!!strcmp(xp->name(), "Porter Duff")) {
         *outPrimary = *outSecondary = -1;
         return;
     }
     BlendFormula blendFormula = static_cast<const PorterDuffXferProcessor*>(xp)->getBlendFormula();
     *outPrimary = blendFormula.fPrimaryOutputType;
     *outSecondary = blendFormula.fSecondaryOutputType;
 }