Make all blending up to GrOptDrawState be handled by the xp/xp factory.

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 55e0c93b23ad03d355ea39969e31c5a7c0cb2eb2..2b4b1334f89828b96cc142a688f8492437f7dcfa 100644
--- a/src/gpu/effects/GrPorterDuffXferProcessor.cpp
+++ b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
@@ -7,6 +7,7 @@
 
 #include "effects/GrPorterDuffXferProcessor.h"
 
+#include "GrBlend.h"
 #include "GrDrawState.h"
 #include "GrInvariantOutput.h"
 #include "GrProcessor.h"
@@ -16,6 +17,25 @@
 #include "gl/builders/GrGLFragmentShaderBuilder.h"
 #include "gl/builders/GrGLProgramBuilder.h"
 
+static bool can_tweak_alpha_for_coverage(GrBlendCoeff dstCoeff, bool isCoverageDrawing) {
+    /*
+     The fractional coverage is f.
+     The src and dst coeffs are Cs and Cd.
+     The dst and src colors are S and D.
+     We want the blend to compute: f*Cs*S + (f*Cd + (1-f))D. By tweaking the source color's alpha
+     we're replacing S with S'=fS. It's obvious that that first term will always be ok. The second
+     term can be rearranged as [1-(1-Cd)f]D. By substituting in the various possibilities for Cd we
+     find that only 1, ISA, and ISC produce the correct destination when applied to S' and D.
+     Also, if we're directly rendering coverage (isCoverageDrawing) then coverage is treated as
+     color by definition.
+     */
+    // TODO: Once we have a CoverageDrawing XP, we don't need to check is CoverageDrawing here
+    return kOne_GrBlendCoeff == dstCoeff ||
+           kISA_GrBlendCoeff == dstCoeff ||
+           kISC_GrBlendCoeff == dstCoeff ||
+           isCoverageDrawing;
+}
+
 class GrGLPorterDuffXferProcessor : public GrGLXferProcessor {
 public:
     GrGLPorterDuffXferProcessor(const GrProcessor&) {}
@@ -42,8 +62,9 @@ private:
 
 ///////////////////////////////////////////////////////////////////////////////
 
-GrPorterDuffXferProcessor::GrPorterDuffXferProcessor(GrBlendCoeff srcBlend, GrBlendCoeff dstBlend)
-    : fSrcBlend(srcBlend), fDstBlend(dstBlend) {
+GrPorterDuffXferProcessor::GrPorterDuffXferProcessor(GrBlendCoeff srcBlend, GrBlendCoeff dstBlend,
+                                                     GrColor constant)
+    : fSrcBlend(srcBlend), fDstBlend(dstBlend), fBlendConstant(constant) {
     this->initClassID<GrPorterDuffXferProcessor>();
 }
 
@@ -60,13 +81,121 @@ GrGLFragmentProcessor* GrPorterDuffXferProcessor::createGLInstance() const {
 }
 
 void GrPorterDuffXferProcessor::onComputeInvariantOutput(GrInvariantOutput* inout) const {
-    inout->setToUnknown(GrInvariantOutput::kWillNot_ReadInput);
+    inout->setToUnknown(GrInvariantOutput::kWill_ReadInput);
 }
 
+GrXferProcessor::OptFlags
+GrPorterDuffXferProcessor::getOptimizations(const GrProcOptInfo& colorPOI,
+                                            const GrProcOptInfo& coveragePOI,
+                                            bool isCoverageDrawing,
+                                            bool colorWriteDisabled,
+                                            bool doesStencilWrite,
+                                            GrColor* color, uint8_t* coverage) {
+    if (colorWriteDisabled) {
+        fSrcBlend = kZero_GrBlendCoeff;
+        fDstBlend = kOne_GrBlendCoeff;
+    }
+
+    bool srcAIsOne;
+    bool hasCoverage;
+    if (isCoverageDrawing) {
+        srcAIsOne = colorPOI.isOpaque() && coveragePOI.isOpaque();
+        hasCoverage = false;
+    } else {
+        srcAIsOne = colorPOI.isOpaque();
+        hasCoverage = !coveragePOI.isSolidWhite();
+    }
+
+    bool dstCoeffIsOne = kOne_GrBlendCoeff == fDstBlend ||
+                         (kSA_GrBlendCoeff == fDstBlend && srcAIsOne);
+    bool dstCoeffIsZero = kZero_GrBlendCoeff == fDstBlend ||
+                         (kISA_GrBlendCoeff == fDstBlend && srcAIsOne);
+
+    // Optimizations when doing RGB Coverage
+    if (coveragePOI.isFourChannelOutput()) {
+        // We want to force our primary output to be alpha * Coverage, where alpha is the alpha
+        // value of the blend the constant. We should already have valid blend coeff's if we are at
+        // a point where we have RGB coverage. We don't need any color stages since the known color
+        // output is already baked into the blendConstant.
+        uint8_t alpha = GrColorUnpackA(fBlendConstant);
+        *color = GrColorPackRGBA(alpha, alpha, alpha, alpha);
+        return GrXferProcessor::kClearColorStages_OptFlag;
+    }
+
+    // When coeffs are (0,1) there is no reason to draw at all, unless
+    // stenciling is enabled. Having color writes disabled is effectively
+    // (0,1).
+    if ((kZero_GrBlendCoeff == fSrcBlend && dstCoeffIsOne)) {
+        if (doesStencilWrite) {
+            *color = 0xffffffff;
+            return GrXferProcessor::kClearColorStages_OptFlag |
+                   GrXferProcessor::kSetCoverageDrawing_OptFlag;
+        } else {
+            fDstBlend = kOne_GrBlendCoeff;
+            return GrXferProcessor::kSkipDraw_OptFlag;
+        }
+    }
+
+    // if we don't have coverage we can check whether the dst
+    // has to read at all. If not, we'll disable blending.
+    if (!hasCoverage) {
+        if (dstCoeffIsZero) {
+            if (kOne_GrBlendCoeff == fSrcBlend) {
+                // if there is no coverage and coeffs are (1,0) then we
+                // won't need to read the dst at all, it gets replaced by src
+                fDstBlend = kZero_GrBlendCoeff;
+                return GrXferProcessor::kNone_Opt;
+            } else if (kZero_GrBlendCoeff == fSrcBlend) {
+                // if the op is "clear" then we don't need to emit a color
+                // or blend, just write transparent black into the dst.
+                fSrcBlend = kOne_GrBlendCoeff;
+                fDstBlend = kZero_GrBlendCoeff;
+                *color = 0;
+                *coverage = 0xff;
+                return GrXferProcessor::kClearColorStages_OptFlag |
+                       GrXferProcessor::kClearCoverageStages_OptFlag;
+            }
+        }
+    } else if (isCoverageDrawing) {
+        // we have coverage but we aren't distinguishing it from alpha by request.
+        return GrXferProcessor::kSetCoverageDrawing_OptFlag;
+    } else {
+        // 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, isCoverageDrawing)) {
+            return GrXferProcessor::kSetCoverageDrawing_OptFlag;
+        }
+        if (dstCoeffIsZero) {
+            if (kZero_GrBlendCoeff == fSrcBlend) {
+                // the source color is not included in the blend
+                // the dst coeff is effectively zero so blend works out to:
+                // (c)(0)D + (1-c)D = (1-c)D.
+                fDstBlend = kISA_GrBlendCoeff;
+                *color = 0xffffffff;
+                return GrXferProcessor::kClearColorStages_OptFlag |
+                       GrXferProcessor::kSetCoverageDrawing_OptFlag;
+            } else if (srcAIsOne) {
+                // the dst coeff is effectively zero so blend works out to:
+                // cS + (c)(0)D + (1-c)D = cS + (1-c)D.
+                // 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;
+            }
+        } 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;
+            return GrXferProcessor::kSetCoverageDrawing_OptFlag;
+        }
+    }
+
+    return GrXferProcessor::kNone_Opt;
+}
 ///////////////////////////////////////////////////////////////////////////////
 
 GrPorterDuffXPFactory::GrPorterDuffXPFactory(GrBlendCoeff src, GrBlendCoeff dst)
-    : fSrc(src), fDst(dst) {
+    : fSrcCoeff(src), fDstCoeff(dst) {
     this->initClassID<GrPorterDuffXPFactory>();
 }
 
@@ -152,16 +281,173 @@ GrXPFactory* GrPorterDuffXPFactory::Create(SkXfermode::Mode mode) {
     }
 }
 
-const GrXferProcessor* GrPorterDuffXPFactory::createXferProcessor() const {
-    return GrPorterDuffXferProcessor::Create(fSrc, fDst);
+GrXferProcessor* GrPorterDuffXPFactory::createXferProcessor(const GrProcOptInfo& colorPOI,
+                                                            const GrProcOptInfo& covPOI) const {
+    if (!covPOI.isFourChannelOutput()) {
+        return GrPorterDuffXferProcessor::Create(fSrcCoeff, fDstCoeff);
+    } else {
+        if (this->supportsRGBCoverage(colorPOI.color(), colorPOI.validFlags())) {
+            SkASSERT(kRGBA_GrColorComponentFlags == colorPOI.validFlags());
+            GrColor blendConstant = GrUnPreMulColor(colorPOI.color());
+            return GrPorterDuffXferProcessor::Create(kConstC_GrBlendCoeff, kISC_GrBlendCoeff,
+                                                     blendConstant);
+        } else {
+            return NULL;
+        }
+    }
 }
 
 bool GrPorterDuffXPFactory::supportsRGBCoverage(GrColor /*knownColor*/,
                                                 uint32_t knownColorFlags) const {
-    if (kOne_GrBlendCoeff == fSrc && kISA_GrBlendCoeff == fDst &&
+    if (kOne_GrBlendCoeff == fSrcCoeff && kISA_GrBlendCoeff == fDstCoeff &&
         kRGBA_GrColorComponentFlags == knownColorFlags) {
         return true;
     }
     return false;
 }
 
+bool GrPorterDuffXPFactory::canApplyCoverage(const GrProcOptInfo& colorPOI,
+                                             const GrProcOptInfo& coveragePOI,
+                                             bool isCoverageDrawing,
+                                             bool colorWriteDisabled) const {
+    bool srcAIsOne = colorPOI.isOpaque() && (!isCoverageDrawing || coveragePOI.isOpaque());
+
+    if (colorWriteDisabled) {
+        return true;
+    }
+
+    bool dstCoeffIsOne = kOne_GrBlendCoeff == fDstCoeff ||
+                         (kSA_GrBlendCoeff == fDstCoeff && srcAIsOne);
+    bool dstCoeffIsZero = kZero_GrBlendCoeff == fDstCoeff ||
+                         (kISA_GrBlendCoeff == fDstCoeff && srcAIsOne);
+
+    if ((kZero_GrBlendCoeff == fSrcCoeff && dstCoeffIsOne)) {
+        return true;
+    }
+
+    // if we don't have coverage we can check whether the dst
+    // has to read at all.
+    if (isCoverageDrawing) {
+        // we have coverage but we aren't distinguishing it from alpha by request.
+        return true;
+    } else {
+        // check whether coverage can be safely rolled into alpha
+        // of if we can skip color computation and just emit coverage
+        if (this->canTweakAlphaForCoverage(isCoverageDrawing)) {
+            return true;
+        }
+        if (dstCoeffIsZero) {
+            if (kZero_GrBlendCoeff == fSrcCoeff) {
+                return true;
+            } else if (srcAIsOne) {
+                return  true;
+            }
+        } else if (dstCoeffIsOne) {
+            return true;
+        }
+    }
+
+    // TODO: once all SkXferEffects are XP's then we will never reads dst here since only XP's
+    // will readDst and PD XP's don't read dst.
+    if ((colorPOI.readsDst() || coveragePOI.readsDst()) &&
+        kOne_GrBlendCoeff == fSrcCoeff && kZero_GrBlendCoeff == fDstCoeff) {
+        return true;
+    }
+
+    return false;
+}
+
+bool GrPorterDuffXPFactory::willBlendWithDst(const GrProcOptInfo& colorPOI,
+                                             const GrProcOptInfo& coveragePOI,
+                                             bool isCoverageDrawing,
+                                             bool colorWriteDisabled) const {
+    if (!(isCoverageDrawing || coveragePOI.isSolidWhite())) {
+        return true;
+    }
+
+    // TODO: once all SkXferEffects are XP's then we will never reads dst here since only XP's
+    // will readDst and PD XP's don't read dst.
+    if ((!colorWriteDisabled && colorPOI.readsDst()) || coveragePOI.readsDst()) {
+        return true;
+    }
+
+    if (GrBlendCoeffRefsDst(fSrcCoeff)) {
+        return true;
+    }
+
+    bool srcAIsOne = colorPOI.isOpaque() && (!isCoverageDrawing || coveragePOI.isOpaque());
+
+    if (!(kZero_GrBlendCoeff == fDstCoeff ||
+          (kISA_GrBlendCoeff == fDstCoeff && srcAIsOne))) {
+        return true;
+    }
+
+    return false;
+}
+
+bool GrPorterDuffXPFactory::canTweakAlphaForCoverage(bool isCoverageDrawing) const {
+    return can_tweak_alpha_for_coverage(fDstCoeff, isCoverageDrawing);
+}
+
+bool GrPorterDuffXPFactory::getOpaqueAndKnownColor(const GrProcOptInfo& colorPOI,
+                                                   const GrProcOptInfo& coveragePOI,
+                                                   GrColor* solidColor,
+                                                   uint32_t* solidColorKnownComponents) const {
+    if (!coveragePOI.isSolidWhite()) {
+        return false;
+    }
+
+    SkASSERT((NULL == solidColor) == (NULL == solidColorKnownComponents));
+
+    GrBlendCoeff srcCoeff = fSrcCoeff;
+    GrBlendCoeff dstCoeff = fDstCoeff;
+
+    // TODO: figure out to merge this simplify with other current optimization code paths and
+    // eventually remove from GrBlend
+    GrSimplifyBlend(&srcCoeff, &dstCoeff, colorPOI.color(), colorPOI.validFlags(),
+                    0, 0, 0);
+
+    bool opaque = kZero_GrBlendCoeff == dstCoeff && !GrBlendCoeffRefsDst(srcCoeff);
+    if (solidColor) {
+        if (opaque) {
+            switch (srcCoeff) {
+                case kZero_GrBlendCoeff:
+                    *solidColor = 0;
+                    *solidColorKnownComponents = kRGBA_GrColorComponentFlags;
+                    break;
+
+                case kOne_GrBlendCoeff:
+                    *solidColor = colorPOI.color();
+                    *solidColorKnownComponents = colorPOI.validFlags();
+                    break;
+
+                // The src coeff should never refer to the src and if it refers to dst then opaque
+                // should have been false.
+                case kSC_GrBlendCoeff:
+                case kISC_GrBlendCoeff:
+                case kDC_GrBlendCoeff:
+                case kIDC_GrBlendCoeff:
+                case kSA_GrBlendCoeff:
+                case kISA_GrBlendCoeff:
+                case kDA_GrBlendCoeff:
+                case kIDA_GrBlendCoeff:
+                default:
+                    SkFAIL("srcCoeff should not refer to src or dst.");
+                    break;
+
+                // TODO: update this once GrPaint actually has a const color.
+                case kConstC_GrBlendCoeff:
+                case kIConstC_GrBlendCoeff:
+                case kConstA_GrBlendCoeff:
+                case kIConstA_GrBlendCoeff:
+                    *solidColorKnownComponents = 0;
+                    break;
+            }
+        } else {
+            solidColorKnownComponents = 0;
+        }
+    }
+    return opaque;
+}
+
+