Potentially optimize some GrGLEffects for known input color values

src/effects/SkLumaColorFilter.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 "SkLumaColorFilter.h"
 
 #include "SkColorPriv.h"
@@ skipping 76 matching lines @@
 
         static EffectKey GenKey(const GrDrawEffect&, const GrGLCaps&) {
             // this class always generates the same code.
             return 0;
         }
 
         virtual void emitCode(GrGLShaderBuilder* builder,
                               const GrDrawEffect&,
                               EffectKey,
                               const char* outputColor,
-                              const char* inputColor,
+                              const GrGLSLExpr4& inputColor,
                               const TransformedCoordsArray&,
                               const TextureSamplerArray&) SK_OVERRIDE {
-            if (NULL == inputColor) {
-                inputColor = "vec4(1)";
-            }
-
             builder->fsCodeAppendf("\tfloat luma = dot(vec3(%f, %f, %f), %s.rgb);\n",
                                    SK_ITU_BT709_LUM_COEFF_R,
                                    SK_ITU_BT709_LUM_COEFF_G,
                                    SK_ITU_BT709_LUM_COEFF_B,
-                                   inputColor);
+                                   inputColor.c_str());
             builder->fsCodeAppendf("\t%s = vec4(0, 0, 0, luma);\n",
                                    outputColor);
 
         }
 
     private:
         typedef GrGLEffect INHERITED;
     };
 
 private:
     virtual bool onIsEqual(const GrEffect&) const SK_OVERRIDE {
         return true;
     }
 };
 
 GrEffectRef* SkLumaColorFilter::asNewEffect(GrContext*) const {
     return LumaColorFilterEffect::Create();
 }
 #endif