Determine whether we can tweakAlphaForCoverage during Pipeline/XP creation.

BUG=skia:

Review URL: https://codereview.chromium.org/927623002

include/gpu/GrInvariantOutput.h

@@ -210,6 +210,7 @@ private:
     bool willUseInputColor() const { return fWillUseInputColor; }
     void resetWillUseInputColor() { fWillUseInputColor = true; }
 
+    bool allStagesMulInput() const { return !fNonMulStageFound; }
     void resetNonMulStageFound() { fNonMulStageFound = false; }
 
     bool isLCDCoverage() const { return fIsLCDCoverage; }

include/gpu/GrXferProcessor.h

@@ -73,6 +73,10 @@ public:
          * Set CoverageDrawing_StateBit
          */
         kSetCoverageDrawing_OptFlag       = 0x10,
+        /**
+         * Can tweak alpha for coverage. Currently this flag should only be used by a batch
+         */
+        kCanTweakAlphaForCoverage_OptFlag = 0x20,
     };
 
     GR_DECL_BITFIELD_OPS_FRIENDS(OptFlags);

src/gpu/GrPipeline.cpp

@@ -102,6 +102,8 @@ GrPipeline::GrPipeline(const GrPipelineBuilder& pipelineBuilder,
     fInitBT.fOverrideColor = fInitBT.fColorIgnored ? GrColor_ILLEGAL : overrideColor;
     fInitBT.fCoverageIgnored = SkToBool(optFlags & GrXferProcessor::kIgnoreCoverage_OptFlag);
     fInitBT.fUsesLocalCoords = usesLocalCoords;
+    fInitBT.fCanTweakAlphaForCoverage =
+        SkToBool(optFlags & GrXferProcessor::kCanTweakAlphaForCoverage_OptFlag);
 }
 
 void GrPipeline::adjustProgramFromOptimizations(const GrPipelineBuilder& pipelineBuilder,

src/gpu/GrPrimitiveProcessor.h

@@ -83,6 +83,7 @@ struct GrPipelineInfo {
     bool fCoverageIgnored;
     GrColor fOverrideColor;
     bool fUsesLocalCoords;
+    bool fCanTweakAlphaForCoverage;
 };
 
 /*

src/gpu/GrProcOptInfo.h

@@ -45,6 +45,7 @@ public:
     bool isSolidWhite() const { return fInOut.isSolidWhite(); }
     bool isOpaque() const { return fInOut.isOpaque(); }
     bool isSingleComponent() const { return fInOut.isSingleComponent(); }
+    bool allStagesMultiplyInput() const { return fInOut.allStagesMulInput(); }
 
     // TODO: Once texture pixel configs quaries are updated, we no longer need this function.
     // For now this function will correctly tell us if we are using LCD text or not and should only

src/gpu/effects/GrPorterDuffXferProcessor.cpp

@@ -330,7 +330,13 @@ PorterDuffXferProcessor::internalGetOptimizations(const GrProcOptInfo& colorPOI,
         // check whether coverage can be safely rolled into alpha
         // of if we can skip color computation and just emit coverage
         if (can_tweak_alpha_for_coverage(fDstBlend)) {
-            return GrXferProcessor::kSetCoverageDrawing_OptFlag;
+            if (colorPOI.allStagesMultiplyInput()) {
+                return GrXferProcessor::kSetCoverageDrawing_OptFlag |
+                       GrXferProcessor::kCanTweakAlphaForCoverage_OptFlag;
+            } else {
+                return GrXferProcessor::kSetCoverageDrawing_OptFlag;
+
+            }
         }
         if (dstCoeffIsZero) {
             if (kZero_GrBlendCoeff == fSrcBlend) {
@@ -346,12 +352,25 @@ PorterDuffXferProcessor::internalGetOptimizations(const GrProcOptInfo& colorPOI,
                 // If Sa is 1 then we can replace Sa with c
                 // and set dst coeff to 1-Sa.
                 fDstBlend = kISA_GrBlendCoeff;
-                return GrXferProcessor::kSetCoverageDrawing_OptFlag;
+                if (colorPOI.allStagesMultiplyInput()) {
+                    return GrXferProcessor::kSetCoverageDrawing_OptFlag |
+                           GrXferProcessor::kCanTweakAlphaForCoverage_OptFlag;
+                } else {
+                    return GrXferProcessor::kSetCoverageDrawing_OptFlag;
+
+                }
             }
         } else if (dstCoeffIsOne) {
             // the dst coeff is effectively one so blend works out to:
             // cS + (c)(1)D + (1-c)D = cS + D.
             fDstBlend = kOne_GrBlendCoeff;
+            if (colorPOI.allStagesMultiplyInput()) {
+                return GrXferProcessor::kSetCoverageDrawing_OptFlag |
+                       GrXferProcessor::kCanTweakAlphaForCoverage_OptFlag;
+            } else {
+                return GrXferProcessor::kSetCoverageDrawing_OptFlag;
+
+            }
             return GrXferProcessor::kSetCoverageDrawing_OptFlag;
         }
     }