Potentially optimize some GrGLEffects for known input color values

src/effects/SkLumaXfermode.cpp

Index: src/effects/SkLumaXfermode.cpp
diff --git a/src/effects/SkLumaXfermode.cpp b/src/effects/SkLumaXfermode.cpp
index aa3d780aa06ffa97ae8f3a4c85e7caf4cefc712c..d1e1ce9425015c9bd55f6a96ea12b4ae4515ea87 100644
--- a/src/effects/SkLumaXfermode.cpp
+++ b/src/effects/SkLumaXfermode.cpp
@@ -39,14 +39,12 @@ SkPMColor SkLumaMaskXfermode::lumaProc(const SkPMColor a, const SkPMColor b) con
 }
 
 template <typename T>
-static inline const T* lumaOpA(SkXfermode::Mode mode,
-                               const T* src, const T* dst) {
+static inline T lumaOpA(SkXfermode::Mode mode, T src, T dst) {
     return SkXfermode::kSrcIn_Mode == mode ? src : dst;
 }
 
 template <typename T>
-static inline const T* lumaOpB(SkXfermode::Mode mode,
-                               const T* src, const T* dst) {
+static inline T lumaOpB(SkXfermode::Mode mode, T src, T dst) {
     return SkXfermode::kSrcIn_Mode == mode ? dst : src;
 }
 
@@ -78,15 +76,15 @@ void SkLumaMaskXfermode::flatten(SkFlattenableWriteBuffer& buffer) const {
 }
 
 SkPMColor SkLumaMaskXfermode::xferColor(SkPMColor src, SkPMColor dst) const {
-    const SkPMColor* a = lumaOpA<SkPMColor>(fMode, &src, &dst);
-    const SkPMColor* b = lumaOpB<SkPMColor>(fMode, &src, &dst);
+    const SkPMColor* a = lumaOpA<const SkPMColor*>(fMode, &src, &dst);
+    const SkPMColor* b = lumaOpB<const SkPMColor*>(fMode, &src, &dst);
     return this->lumaProc(*a, *b);
 }
 
 void SkLumaMaskXfermode::xfer32(SkPMColor dst[], const SkPMColor src[],
                                 int count, const SkAlpha aa[]) const {
-    const SkPMColor* a = lumaOpA<SkPMColor>(fMode, src, dst);
-    const SkPMColor* b = lumaOpB<SkPMColor>(fMode, src, dst);
+    const SkPMColor* a = lumaOpA<const SkPMColor*>(fMode, src, dst);
+    const SkPMColor* b = lumaOpB<const SkPMColor*>(fMode, src, dst);
 
     if (aa) {
         for (int i = 0; i < count; ++i) {
@@ -157,7 +155,7 @@ public:
                           const GrDrawEffect&,
                           EffectKey,
                           const char* outputColor,
-                          const char* inputColor,
+                          const GrGLSLExpr4& inputColor,
                           const TransformedCoordsArray&,
                           const TextureSamplerArray&) SK_OVERRIDE;
 
@@ -206,30 +204,26 @@ void GrGLLumaMaskEffect::emitCode(GrGLShaderBuilder* builder,
                                   const GrDrawEffect& effect,
                                   EffectKey key,
                                   const char* outputColor,
-                                  const char* inputColor,
+                                  const GrGLSLExpr4& inputColor,
                                   const TransformedCoordsArray&,
                                   const TextureSamplerArray& samplers) {
 
     const GrLumaMaskEffect& lumaEffect = effect.castEffect<GrLumaMaskEffect>();
-    const char* dstColor = builder->dstColor();
-    SkASSERT(NULL != dstColor);
-    if (NULL == inputColor) {
-        inputColor = "vec4(1)";
-    }
+    GrGLSLExpr4 dstColor(builder->dstColor());
 
-    const char *opA = lumaOpA<char>(lumaEffect.getMode(), inputColor, dstColor);
-    const char *opB = lumaOpB<char>(lumaEffect.getMode(), inputColor, dstColor);
+    const GrGLSLExpr4& opA = lumaOpA(lumaEffect.getMode(), inputColor, dstColor);
+    const GrGLSLExpr4& opB = lumaOpB(lumaEffect.getMode(), inputColor, dstColor);
 
     builder->fsCodeAppendf("\t\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,
-                           opB);
+                           opB.c_str());
     if (SkXfermode::kSrcOver_Mode == lumaEffect.getMode()) {
-        builder->fsCodeAppendf("\t\tvec4 newB = %s;\n\t\tif (newB.a > 0.0) { newB *= luma / newB.a; }\n\t\tnewB.a = luma;\n", opB);
-        builder->fsCodeAppendf("\t\t%s = newB + %s * (1.0 - luma); \n", outputColor, opA);
+        builder->fsCodeAppendf("\t\tvec4 newB = %s;\n\t\tif (newB.a > 0.0) { newB *= luma / newB.a; }\n\t\tnewB.a = luma;\n", opB.c_str());
+        builder->fsCodeAppendf("\t\t%s = newB + %s * (1.0 - luma); \n", outputColor, opA.c_str());
     } else {
-        builder->fsCodeAppendf("\t\t%s = %s * luma;\n", outputColor, opA);
+        builder->fsCodeAppendf("\t\t%s = %s * luma;\n", outputColor, opA.c_str());
     }
 }