Cleanup GPU gamut transformation code

src/gpu/glsl/GrGLSLShaderBuilder.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrSwizzle.h"
 #include "glsl/GrGLSLShaderBuilder.h"
 #include "glsl/GrGLSLCaps.h"
@@ skipping 115 matching lines @@
     } else {
         this->codeAppend((GrGLSLExpr4(modulation) * GrGLSLExpr4(lookup)).c_str());
     }
 }
 
 void GrGLSLShaderBuilder::appendColorGamutXform(SkString* out,
                                                 const char* srcColor,
                                                 GrGLSLColorSpaceXformHelper* colorXformHelper) {
     // Our color is (r, g, b, a), but we want to multiply (r, g, b, 1) by our matrix, then
     // re-insert the original alpha. The supplied srcColor is likely to be of the form
-    // "texture(...)", and we don't want to evaluate that twice.
-    //
-    // Worse: We can't do the transformation on premultiplied colors, so if the source is premul,
-    // we need to unpremul, transform, then multiply again. Anyways, we wrap all of the work in a
-    // function.
+    // "texture(...)", and we don't want to evaluate that twice, so wrap everything in a function.
     static const GrGLSLShaderVar gColorGamutXformArgs[] = {
         GrGLSLShaderVar("color", kVec4f_GrSLType),
         GrGLSLShaderVar("xform", kMat44f_GrSLType),
     };
     SkString functionBody;
-    if (kPremul_SkAlphaType == colorXformHelper->alphaType()) {
-        // Unpremultiply
-        functionBody.append("\tfloat nonZeroAlpha = max(color.a, 0.00001);\n"
-                            "\tcolor.rgb = color.rgb / nonZeroAlpha;\n");
-    }
     // Gamut xform, clamp to destination gamut
     functionBody.append("\tcolor.rgb = clamp((xform * vec4(color.rgb, 1.0)).rgb, 0.0, 1.0);\n");
-    if (kPremul_SkAlphaType == colorXformHelper->alphaType()) {
-        // Re-multiply by alpha
-        functionBody.append("\tcolor.rgb = color.rgb * nonZeroAlpha;\n");
-    }
     functionBody.append("\treturn color;");
     SkString colorGamutXformFuncName;
     this->emitFunction(kVec4f_GrSLType,
                        "colorGamutXform",
                        SK_ARRAY_COUNT(gColorGamutXformArgs),
                        gColorGamutXformArgs,
                        functionBody.c_str(),
                        &colorGamutXformFuncName);
 
     out->appendf("%s(%s, %s)", colorGamutXformFuncName.c_str(), srcColor,
@@ skipping 86 matching lines @@
     // append the 'footer' to code
     this->code().append("}");
 
     for (int i = 0; i <= fCodeIndex; i++) {
         fCompilerStrings[i] = fShaderStrings[i].c_str();
         fCompilerStringLengths[i] = (int)fShaderStrings[i].size();
     }
 
     fFinalized = true;
 }