Potentially optimize some GrGLEffects for known input color values

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 98 matching lines @@
         GLEffect(const GrBackendEffectFactory& factory,
                     const GrDrawEffect& e)
         : GrGLEffect(factory)
         , fPrevThreshold(-SK_Scalar1) {
         }
 
         virtual void emitCode(GrGLShaderBuilder* builder,
                               const GrDrawEffect& drawEffect,
                               EffectKey key,
                               const char* outputColor,
-                              const char* inputColor,
+                              const GrGLSLExpr4& inputColor,
                               const TransformedCoordsArray& coords,
                               const TextureSamplerArray& samplers) SK_OVERRIDE {
             // put bitmap color in "color"
             builder->fsCodeAppend("\t\tvec4 color = ");
             builder->fsAppendTextureLookup(samplers[0], coords[0].c_str(), coords[0].type());
             builder->fsCodeAppend(";\n");
 
             // put alpha from mask texture in "mask"
             builder->fsCodeAppend("\t\tfloat mask = ");
             builder->fsAppendTextureLookup(samplers[1], coords[1].c_str(), coords[1].type());
@@ skipping 13 matching lines @@
                                     "\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->fsCodeAppendf("color = %s = %s;\n", outputColor,
-                                   (GrGLSLExpr4(inputColor) * GrGLSLExpr4("color")).c_str());
+                                   (inputColor * GrGLSLExpr4("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