Draft change to start pulling uniform color into GP

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 6255e4a9138773db51495591f9d7244c270f3727..8557bd2745f9358572ea9abe26523304df6747c9 100644
--- a/src/gpu/effects/GrPorterDuffXferProcessor.cpp
+++ b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
@@ -66,11 +66,28 @@ public:
             }
         }
         
-        fsBuilder->codeAppendf("%s = %s * %s;", args.fOutputPrimary, args.fInputColor,
-                               args.fInputCoverage);
-        if (GrPorterDuffXferProcessor::kCombineWithDst_PrimaryOutputType == xp.primaryOutputType()){
-            fsBuilder->codeAppendf("%s += (vec4(1.0) - %s) * %s;", args.fOutputPrimary,
-                                   args.fInputCoverage, fsBuilder->dstColor());
+        switch (xp.primaryOutputType()) {
+            case GrPorterDuffXferProcessor::kNone_PrimaryOutputType:
+                fsBuilder->codeAppendf("%s = vec4(0);", args.fOutputPrimary);
+                break;
+            case GrPorterDuffXferProcessor::kColor_PrimaryOutputType:
+                fsBuilder->codeAppendf("%s = %s;", args.fOutputPrimary, args.fInputColor);
+                break;
+            case GrPorterDuffXferProcessor::kCoverage_PrimaryOutputType:
+                fsBuilder->codeAppendf("%s = %s;", args.fOutputPrimary, args.fInputCoverage);
+                break;
+            case GrPorterDuffXferProcessor::kModulate_PrimaryOutputType:
+            case GrPorterDuffXferProcessor::kCombineWithDst_PrimaryOutputType:
+                fsBuilder->codeAppendf("%s = %s * %s;", args.fOutputPrimary, args.fInputColor,
+                                       args.fInputCoverage);
+                if (GrPorterDuffXferProcessor::kCombineWithDst_PrimaryOutputType ==
+                    xp.primaryOutputType()){
+                    fsBuilder->codeAppendf("%s += (vec4(1.0) - %s) * %s;", args.fOutputPrimary,
+                                           args.fInputCoverage, fsBuilder->dstColor());
+                }
+                break;
+            default:
+                SkFAIL("Unexpected Primary Output");
         }
     }
 
@@ -139,6 +156,19 @@ GrPorterDuffXferProcessor::getOptimizations(const GrProcOptInfo& colorPOI,
 void GrPorterDuffXferProcessor::calcOutputTypes(GrXferProcessor::OptFlags optFlags,
                                                 const GrDrawTargetCaps& caps,
                                                 bool hasSolidCoverage, bool readsDst) {
+    if (optFlags & kClearColorStages_OptFlag) {
+        if (optFlags & kClearCoverageStages_OptFlag) {
+            fPrimaryOutputType = kNone_PrimaryOutputType;
+            return;
+        } else {
+            fPrimaryOutputType = kCoverage_PrimaryOutputType;
+            return;
+        }
+    } else if (optFlags & kClearCoverageStages_OptFlag) {
+        fPrimaryOutputType = kColor_PrimaryOutputType;
+        return;
+    }
+
     // If we do have coverage determine whether it matters.  Dual source blending is expensive so
     // we don't do it if we are doing coverage drawing.  If we aren't then We always do dual source
     // blending if we have any effective coverage stages OR the geometry processor doesn't emits