Express (GLSL expression, possibly known value) pairs as a class

src/effects/SkBitmapAlphaThresholdShader.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapAlphaThresholdShader.h"
 
 class BATShader : public SkShader {
@@ skipping 131 matching lines @@
                                     "\t\t\t\tfloat scale = thresh / color.a;\n"
                                     "\t\t\t\tcolor.rgb *= scale;\n"
                                     "\t\t\t\tcolor.a = thresh;\n"
                                     "\t\t\t}\n"
                                     "\t\t} else if (color.a < thresh) {\n"
                                     "\t\t\tfloat scale = thresh / color.a;\n"
                                     "\t\t\tcolor.rgb *= scale;\n"
                                     "\t\t\tcolor.a = thresh;\n"
                                     "\t\t}\n");
 
-            builder->fsCodeAppend("color = ");
-            SkString outStr;
-            outStr.appendf("\t\t%s = ", outputColor);
-            GrGLSLModulatef<4>(&outStr, inputColor, "color");
-            outStr.append(";\n");
-            builder->fsCodeAppend(outStr.c_str());
+            builder->fsCodeAppendf("color = %s = %s;\n", outputColor,
+                                   (GrGLSLExpr<4>(inputColor) * GrGLSLExpr<4>("color")).c_str());
         }
 
         virtual void setData(const GrGLUniformManager& uman, const GrDrawEffect& e) SK_OVERRIDE {
             const ThresholdEffect& effect = e.castEffect<ThresholdEffect>();
             if (fPrevThreshold != effect.fThreshold) {
                 uman.set1f(fThresholdUniHandle, effect.fThreshold);
             }
         }
 
     private:
@@ skipping 104 matching lines @@
     GrEffectRef* effect = ThresholdEffect::Create(bmpTexture, bmpMatrix,
                                                   maskTexture, maskMatrix,
                                                   fThreshold);
 
     GrUnlockAndUnrefCachedBitmapTexture(bmpTexture);
 
     return effect;
 }
 
 #endif