Make GrGLConfigConversionEffect work for Imagination and some other GPUs.

src/gpu/gl/GrGLShaderBuilder.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gl/GrGLShaderBuilder.h"
 #include "gl/GrGLProgram.h"
 #include "gl/GrGLUniformHandle.h"
@@ skipping 518 matching lines @@
 
             // Effects have no way to communicate zeros, they treat an empty string as ones.
             this->nameVariable(&inColorName, '\0', "input");
             this->fsCodeAppendf("\tvec4 %s = %s;\n", inColorName.c_str(), inColor.c_str());
             inColor = inColorName;
         }
 
         // create var to hold stage result
         SkString outColorName;
         this->nameVariable(&outColorName, '\0', "output");
-        this->fsCodeAppendf("\tvec4 %s;\n", outColorName.c_str());
+
+        if (kImagination_GrGLVendor == this->ctxInfo().vendor() &&
+            kPVRRogueHood_GrGLRenderer == this->ctxInfo().renderer())

[bsalomon, 2014/07/01 13:54:51]

Can't you have a temporary highp var in the config conversion effect where you
compute the result and then assign that to the mediump output var at the end of
the effect. Does that not work?


vec4 output_StageN;
{
   highp vec4 outputH = // config conversion stuff, texture lookup etc.

   output_StageN = outputH
}

+            this->fsCodeAppendf("\thighp vec4 %s;\n", outColorName.c_str());
+        else
+            this->fsCodeAppendf("\tvec4 %s;\n", outColorName.c_str());
+
         outColor = outColorName;
 
 
         programEffectsBuilder->emitEffect(stage,
                                           effectKeys[e],
                                           outColor.c_str(),
                                           inColor.isOnes() ? NULL : inColor.c_str(),
                                           fCodeStage.stageIndex());
 
         inColor = outColor;
@@ skipping 440 matching lines @@
 
     GrGLPathTexGenProgramEffectsBuilder pathTexGenEffectsBuilder(this,
                                                                  effectCnt);
     this->INHERITED::createAndEmitEffects(&pathTexGenEffectsBuilder,
                                           effectStages,
                                           effectKeys,
                                           effectCnt,
                                           inOutFSColor);
     return pathTexGenEffectsBuilder.finish();
 }