Fix various issues with framebuffer fetch

src/gpu/glsl/GrGLSLFragmentShaderBuilder.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 "GrGLSLFragmentShaderBuilder.h"
 #include "GrRenderTarget.h"
 #include "GrRenderTargetPriv.h"
 #include "gl/GrGLGpu.h"
 #include "glsl/GrGLSL.h"
 #include "glsl/GrGLSLCaps.h"
 #include "glsl/GrGLSLProgramBuilder.h"
 #include "glsl/GrGLSLUniformHandler.h"
 #include "glsl/GrGLSLVarying.h"
 
-const char* GrGLSLFragmentShaderBuilder::kDstTextureColorName = "_dstColor";
+const char* GrGLSLFragmentShaderBuilder::kDstColorName = "_dstColor";
 
 static const char* sample_offset_array_name(GrGLSLFPFragmentBuilder::Coordinates coords) {
     static const char* kArrayNames[] = {
         "deviceSpaceSampleOffsets",
         "windowSpaceSampleOffsets"
     };
     return kArrayNames[coords];
 
     GR_STATIC_ASSERT(0 == GrGLSLFPFragmentBuilder::kSkiaDevice_Coordinates);
     GR_STATIC_ASSERT(1 == GrGLSLFPFragmentBuilder::kGLSLWindow_Coordinates);
@@ skipping 228 matching lines @@
     if (glslCaps->fbFetchSupport()) {
         this->addFeature(1 << kFramebufferFetch_GLSLPrivateFeature,
                          glslCaps->fbFetchExtensionString());
 
         // Some versions of this extension string require declaring custom color output on ES 3.0+
         const char* fbFetchColorName = glslCaps->fbFetchColorName();
         if (glslCaps->fbFetchNeedsCustomOutput()) {
             this->enableCustomOutput();
             fOutputs[fCustomColorOutputIndex].setTypeModifier(GrShaderVar::kInOut_TypeModifier);
             fbFetchColorName = DeclaredColorOutputName();
+            // Set the dstColor to an intermediate variable so we don't override it with the output
+            this->codeAppendf("vec4 %s = %s;", kDstColorName, fbFetchColorName);
         }
-        return fbFetchColorName;
-    } else {
-        return kDstTextureColorName;
     }
+    return kDstColorName;
 }
 
 void GrGLSLFragmentShaderBuilder::enableAdvancedBlendEquationIfNeeded(GrBlendEquation equation) {
     SkASSERT(GrBlendEquationIsAdvanced(equation));
 
     const GrGLSLCaps& caps = *fProgramBuilder->glslCaps();
     if (!caps.mustEnableAdvBlendEqs()) {
         return;
     }
 
@@ skipping 107 matching lines @@
     fMangleString.appendf("_c%d", fSubstageIndices[fSubstageIndices.count() - 2]);
 }
 
 void GrGLSLFragmentShaderBuilder::onAfterChildProcEmitCode() {
     SkASSERT(fSubstageIndices.count() >= 2);
     fSubstageIndices.pop_back();
     fSubstageIndices.back()++;
     int removeAt = fMangleString.findLastOf('_');
     fMangleString.remove(removeAt, fMangleString.size() - removeAt);
 }