Added GrGLBlend.h|cpp with helper function AppendPorterDuffBlend() in preparation for SkComposeShad…

src/gpu/effects/GrPorterDuffXferProcessor.cpp

Index: src/gpu/effects/GrPorterDuffXferProcessor.cpp
diff --git a/src/gpu/effects/GrPorterDuffXferProcessor.cpp b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
index b6b57aefead08b0ccbcd477c73a6e28d53ad1f2c..0e1bc514698e214cdf5e1900f9c330609d0c9b42 100644
--- a/src/gpu/effects/GrPorterDuffXferProcessor.cpp
+++ b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
@@ -13,6 +13,7 @@
 #include "GrProcOptInfo.h"
 #include "GrTypes.h"
 #include "GrXferProcessor.h"
+#include "gl/GrGLBlend.h"
 #include "gl/GrGLXferProcessor.h"
 #include "gl/builders/GrGLFragmentShaderBuilder.h"
 #include "gl/builders/GrGLProgramBuilder.h"
@@ -488,50 +489,6 @@ private:
 
 ///////////////////////////////////////////////////////////////////////////////
 
-static bool append_porterduff_term(GrGLXPFragmentBuilder* fsBuilder, SkXfermode::Coeff coeff,
-                                   const char* colorName, const char* srcColorName,
-                                   const char* dstColorName, bool hasPrevious) {
-    if (SkXfermode::kZero_Coeff == coeff) {
-        return hasPrevious;
-    } else {
-        if (hasPrevious) {
-            fsBuilder->codeAppend(" + ");
-        }
-        fsBuilder->codeAppendf("%s", colorName);
-        switch (coeff) {
-            case SkXfermode::kOne_Coeff:
-                break;
-            case SkXfermode::kSC_Coeff:
-                fsBuilder->codeAppendf(" * %s", srcColorName);
-                break;
-            case SkXfermode::kISC_Coeff:
-                fsBuilder->codeAppendf(" * (vec4(1.0) - %s)", srcColorName);
-                break;
-            case SkXfermode::kDC_Coeff:
-                fsBuilder->codeAppendf(" * %s", dstColorName);
-                break;
-            case SkXfermode::kIDC_Coeff:
-                fsBuilder->codeAppendf(" * (vec4(1.0) - %s)", dstColorName);
-                break;
-            case SkXfermode::kSA_Coeff:
-                fsBuilder->codeAppendf(" * %s.a", srcColorName);
-                break;
-            case SkXfermode::kISA_Coeff:
-                fsBuilder->codeAppendf(" * (1.0 - %s.a)", srcColorName);
-                break;
-            case SkXfermode::kDA_Coeff:
-                fsBuilder->codeAppendf(" * %s.a", dstColorName);
-                break;
-            case SkXfermode::kIDA_Coeff:
-                fsBuilder->codeAppendf(" * (1.0 - %s.a)", dstColorName);
-                break;
-            default:
-                SkFAIL("Unsupported Blend Coeff");
-        }
-        return true;
-    }
-}
-
 class GLShaderPDXferProcessor : public GrGLXferProcessor {
 public:
     static void GenKey(const GrProcessor& processor, GrProcessorKeyBuilder* b) {
@@ -545,17 +502,7 @@ private:
         const ShaderPDXferProcessor& xp = proc.cast<ShaderPDXferProcessor>();
         GrGLXPFragmentBuilder* fsBuilder = pb->getFragmentShaderBuilder();
 
-        SkXfermode::Coeff srcCoeff, dstCoeff;
-        SkXfermode::ModeAsCoeff(xp.getXfermode(), &srcCoeff, &dstCoeff);
-
-        fsBuilder->codeAppendf("%s =", outColor);
-        // append src blend
-        bool didAppend = append_porterduff_term(fsBuilder, srcCoeff, srcColor, srcColor, dstColor,
-                                                false);
-        // append dst blend
-        SkAssertResult(append_porterduff_term(fsBuilder, dstCoeff, dstColor, srcColor, dstColor,
-                                              didAppend));
-        fsBuilder->codeAppend(";");
+        GrGLBlend::AppendPorterDuffBlend(fsBuilder, srcColor, dstColor, outColor, xp.getXfermode());
     }
 
     void onSetData(const GrGLProgramDataManager&, const GrXferProcessor&) override {}
@@ -824,4 +771,3 @@ void GrPorterDuffXPFactory::TestGetXPOutputTypes(const GrXferProcessor* xp,
     *outPrimary = blendFormula.fPrimaryOutputType;
     *outSecondary = blendFormula.fSecondaryOutputType;
 }
-