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..52ef75572d099c2bc6c31dd48f3375ecdd16078a 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) {

[bsalomon, 2014/12/08 15:38:51]

Why does this take a constant? Shouldn't it deduce the constant from the
invariant output of the color stages?

[egdaniel, 2014/12/08 16:24:01]

The currently the constant gets deduced during the createXferProcessor(...) when
we go from XPF->XP. I choose here since this is the same spot where we are
looking for RGB coverage and changing coeffs. The other option would be to put
the logic in the getOptimizations call on XP, but setting the blend constant
doesn't really feel like an optimization as much as a requirement.

Another option would be for the constructor to take in the color and coverage
invariants and shift the logic from the createXferProcessor to the XP::Create()
or XP:ctor() functions.

[bsalomon, 2014/12/08 18:35:22]

You can ignore my comment. I was thinking this was the PDXPF cons not PDXP.
lgtm

     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.isSingleComponent()) {
+        // 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.isSingleComponent()) {
+        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;
+}
+
+