Make GrGLConfigConversionEffect work for Imagination and some other GPUs.

src/gpu/effects/GrConfigConversionEffect.cpp

Index: src/gpu/effects/GrConfigConversionEffect.cpp
diff --git a/src/gpu/effects/GrConfigConversionEffect.cpp b/src/gpu/effects/GrConfigConversionEffect.cpp
index 07529d04ff3839a2378a4fa14141acb74919e3ab..d7ba6865c96be6ce8724f9be29004958bc18e958 100644
--- a/src/gpu/effects/GrConfigConversionEffect.cpp
+++ b/src/gpu/effects/GrConfigConversionEffect.cpp
@@ -30,19 +30,26 @@ public:
                           const char* inputColor,
                           const TransformedCoordsArray& coords,
                           const TextureSamplerArray& samplers) SK_OVERRIDE {
-        builder->fsCodeAppendf("\t\t%s = ", outputColor);
+        // Using highp for GLES here in order to avoid some precision issues on specific GPUs.
+        GrGLShaderVar tmpVar("tmpColor", kVec4f_GrSLType, 0, GrGLShaderVar::kHigh_Precision);
+        SkString tmpDecl;
+        tmpVar.appendDecl(builder->ctxInfo(), &tmpDecl);
+        builder->fsCodeAppendf("%s;", tmpDecl.c_str());
+
+        builder->fsCodeAppendf("%s = ", tmpVar.c_str());
         builder->fsAppendTextureLookup(samplers[0], coords[0].c_str(), coords[0].type());
-        builder->fsCodeAppend(";\n");
+        builder->fsCodeAppend(";");
+
         if (GrConfigConversionEffect::kNone_PMConversion == fPMConversion) {
             SkASSERT(fSwapRedAndBlue);
-            builder->fsCodeAppendf("\t%s = %s.bgra;\n", outputColor, outputColor);
+            builder->fsCodeAppendf("%s = %s.bgra;", outputColor, tmpVar.c_str());
         } else {
             const char* swiz = fSwapRedAndBlue ? "bgr" : "rgb";
             switch (fPMConversion) {
                 case GrConfigConversionEffect::kMulByAlpha_RoundUp_PMConversion:
                     builder->fsCodeAppendf(
-                        "\t\t%s = vec4(ceil(%s.%s * %s.a * 255.0) / 255.0, %s.a);\n",
-                        outputColor, outputColor, swiz, outputColor, outputColor);
+                        "%s = vec4(ceil(%s.%s * %s.a * 255.0) / 255.0, %s.a);",
+                        tmpVar.c_str(), tmpVar.c_str(), swiz, tmpVar.c_str(), tmpVar.c_str());
                     break;
                 case GrConfigConversionEffect::kMulByAlpha_RoundDown_PMConversion:
                     // Add a compensation(0.001) here to avoid the side effect of the floor operation.
@@ -50,21 +57,24 @@ public:
                     // is less than the integer value converted from  %s.r by 1 when the %s.r is
                     // converted from the integer value 2^n, such as 1, 2, 4, 8, etc.
                     builder->fsCodeAppendf(
-                        "\t\t%s = vec4(floor(%s.%s * %s.a * 255.0 + 0.001) / 255.0, %s.a);\n",
-                        outputColor, outputColor, swiz, outputColor, outputColor);
+                        "%s = vec4(floor(%s.%s * %s.a * 255.0 + 0.001) / 255.0, %s.a);",
+                        tmpVar.c_str(), tmpVar.c_str(), swiz, tmpVar.c_str(), tmpVar.c_str());
                     break;
                 case GrConfigConversionEffect::kDivByAlpha_RoundUp_PMConversion:
-                    builder->fsCodeAppendf("\t\t%s = %s.a <= 0.0 ? vec4(0,0,0,0) : vec4(ceil(%s.%s / %s.a * 255.0) / 255.0, %s.a);\n",
-                        outputColor, outputColor, outputColor, swiz, outputColor, outputColor);
+                    builder->fsCodeAppendf(
+                        "%s = %s.a <= 0.0 ? vec4(0,0,0,0) : vec4(ceil(%s.%s / %s.a * 255.0) / 255.0, %s.a);",
+                        tmpVar.c_str(), tmpVar.c_str(), tmpVar.c_str(), swiz, tmpVar.c_str(), tmpVar.c_str());
                     break;
                 case GrConfigConversionEffect::kDivByAlpha_RoundDown_PMConversion:
-                    builder->fsCodeAppendf("\t\t%s = %s.a <= 0.0 ? vec4(0,0,0,0) : vec4(floor(%s.%s / %s.a * 255.0) / 255.0, %s.a);\n",
-                        outputColor, outputColor, outputColor, swiz, outputColor, outputColor);
+                    builder->fsCodeAppendf(
+                        "%s = %s.a <= 0.0 ? vec4(0,0,0,0) : vec4(floor(%s.%s / %s.a * 255.0) / 255.0, %s.a);",
+                        tmpVar.c_str(), tmpVar.c_str(), tmpVar.c_str(), swiz, tmpVar.c_str(), tmpVar.c_str());
                     break;
                 default:
                     SkFAIL("Unknown conversion op.");
                     break;
             }
+            builder->fsCodeAppendf("%s = %s;", outputColor, tmpVar.c_str());
         }
         SkString modulate;
         GrGLSLMulVarBy4f(&modulate, 2, outputColor, inputColor);