Fix various issues with framebuffer fetch

src/gpu/glsl/GrGLSLXferProcessor.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 "glsl/GrGLSLXferProcessor.h"
 
 #include "GrXferProcessor.h"
 #include "glsl/GrGLSLFragmentShaderBuilder.h"
 #include "glsl/GrGLSLProgramDataManager.h"
 #include "glsl/GrGLSLUniformHandler.h"
 
 void GrGLSLXferProcessor::emitCode(const EmitArgs& args) {
     if (!args.fXP.willReadDstColor()) {
         this->emitOutputsForBlendState(args);
         return;
     }
 
     GrGLSLXPFragmentBuilder* fragBuilder = args.fXPFragBuilder;
     GrGLSLUniformHandler* uniformHandler = args.fUniformHandler;
     const char* dstColor = fragBuilder->dstColor();
 
+    bool needsLocalOutColor = false;
+
     if (args.fXP.getDstTexture()) {
         bool topDown = kTopLeft_GrSurfaceOrigin == args.fXP.getDstTexture()->origin();
 
         if (args.fInputCoverage) {
             // We don't think any shaders actually output negative coverage, but just as a safety
             // check for floating point precision errors we compare with <= here
             fragBuilder->codeAppendf("if (all(lessThanEqual(%s, vec4(0)))) {"
                                      "    discard;"
                                      "}", args.fInputCoverage);
         }
@@ skipping 17 matching lines @@
         fragBuilder->codeAppendf("vec2 _dstTexCoord = (%s.xy - %s) * %s;",
                                  fragPos, dstTopLeftName, dstCoordScaleName);
 
         if (!topDown) {
             fragBuilder->codeAppend("_dstTexCoord.y = 1.0 - _dstTexCoord.y;");
         }
 
         fragBuilder->codeAppendf("vec4 %s = ", dstColor);
         fragBuilder->appendTextureLookup(args.fTexSamplers[0], "_dstTexCoord", kVec2f_GrSLType);
         fragBuilder->codeAppend(";");
+    } else {
+        needsLocalOutColor = args.fGLSLCaps->requiresLocalOutputColorForFBFetch();
+    }
+
+    const char* outColor = "_localColorOut";
+    if (!needsLocalOutColor) {
+        outColor = args.fOutputPrimary;
+    } else {
+        fragBuilder->codeAppendf("vec4 %s;", outColor);
     }
 
     this->emitBlendCodeForDstRead(fragBuilder,
                                   uniformHandler,
                                   args.fInputColor,
                                   args.fInputCoverage,
                                   dstColor,
-                                  args.fOutputPrimary,
+                                  outColor,
                                   args.fOutputSecondary,
                                   args.fXP);
+    if (needsLocalOutColor) {
+        fragBuilder->codeAppendf("%s = %s;", args.fOutputPrimary, outColor);
+    }
 }
 
 void GrGLSLXferProcessor::setData(const GrGLSLProgramDataManager& pdm, const GrXferProcessor& xp) {
     if (xp.getDstTexture()) {
         if (fDstTopLeftUni.isValid()) {
             pdm.set2f(fDstTopLeftUni, static_cast<float>(xp.dstTextureOffset().fX),
                       static_cast<float>(xp.dstTextureOffset().fY));
             pdm.set2f(fDstScaleUni, 1.f / xp.getDstTexture()->width(),
                       1.f / xp.getDstTexture()->height());
         } else {
@@ skipping 17 matching lines @@
             fragBuilder->codeAppendf("%s *= %s;", outColor, srcCoverage);
             fragBuilder->codeAppendf("%s = %s;", outColorSecondary, srcCoverage);
         } else {
             fragBuilder->codeAppendf("%s = vec4(1.0);", outColorSecondary);
         }
     } else if (srcCoverage) {
         fragBuilder->codeAppendf("%s = %s * %s + (vec4(1.0) - %s) * %s;",
                                  outColor, srcCoverage, outColor, srcCoverage, dstColor);
     }
 }