Make GrGLConfigConversionEffect work for Imagination and some other GPUs.

src/gpu/gl/GrGLShaderBuilder.cpp

Index: src/gpu/gl/GrGLShaderBuilder.cpp
diff --git a/src/gpu/gl/GrGLShaderBuilder.cpp b/src/gpu/gl/GrGLShaderBuilder.cpp
index c5df4c803ce501011616bef7c7d458d1668d8996..d5e056bb908c129a8a3212561b42809c2f29af1e 100644
--- a/src/gpu/gl/GrGLShaderBuilder.cpp
+++ b/src/gpu/gl/GrGLShaderBuilder.cpp
@@ -536,7 +536,13 @@ void GrGLShaderBuilder::createAndEmitEffects(GrGLProgramEffectsBuilder* programE
         // 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;