Revert of Use dst copies in porter duffer XP to correctly render certain blends. (patchset #4 id:60001 of https://codereview.chromium.org/914003003/)

Reason for revert:
Failing GLProgramTest passing in stupid coeffs

Original issue's description:
> Use dst copies in porter duffer XP to correctly render certain blends.
>
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/997c6358d94e188b1a7b89a4f86e24cbe0f5a164

TBR=bsalomon@google.com,joshualitt@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/923153003

10 files changed, 83 insertions, 180 deletions

diff --git a/src/effects/SkArithmeticMode_gpu.cpp b/src/effects/SkArithmeticMode_gpu.cpp
index e068c9dc37..469f5b1adb 100644
--- a/src/effects/SkArithmeticMode_gpu.cpp
+++ b/src/effects/SkArithmeticMode_gpu.cpp
@@ -304,12 +304,11 @@ GrArithmeticXPFactory::GrArithmeticXPFactory(float k1, float k2, float k3, float
 }
 
 GrXferProcessor*
-GrArithmeticXPFactory::onCreateXferProcessor(const GrDrawTargetCaps& caps,
-                                             const GrProcOptInfo& colorPOI,
+GrArithmeticXPFactory::onCreateXferProcessor(const GrProcOptInfo& colorPOI,
                                              const GrProcOptInfo& coveragePOI,
                                              const GrDeviceCoordTexture* dstCopy) const {
     return ArithmeticXP::Create(fK1, fK2, fK3, fK4, fEnforcePMColor, dstCopy,
-                                this->willReadDstColor(caps, colorPOI, coveragePOI));
+                                this->willReadDstColor(colorPOI, coveragePOI));
 }
 
 
diff --git a/src/effects/SkArithmeticMode_gpu.h b/src/effects/SkArithmeticMode_gpu.h
index 546902dd50..822e7bde1e 100644
--- a/src/effects/SkArithmeticMode_gpu.h
+++ b/src/effects/SkArithmeticMode_gpu.h
@@ -96,13 +96,11 @@ public:
 private:
     GrArithmeticXPFactory(float k1, float k2, float k3, float k4, bool enforcePMColor); 
 
-    GrXferProcessor* onCreateXferProcessor(const GrDrawTargetCaps& caps,
-                                           const GrProcOptInfo& colorPOI,
+    GrXferProcessor* onCreateXferProcessor(const GrProcOptInfo& colorPOI,
                                            const GrProcOptInfo& coveragePOI,
                                            const GrDeviceCoordTexture* dstCopy) const SK_OVERRIDE; 
 
-    bool willReadDstColor(const GrDrawTargetCaps& caps,
-                          const GrProcOptInfo& colorPOI,
+    bool willReadDstColor(const GrProcOptInfo& colorPOI,
                           const GrProcOptInfo& coveragePOI) const SK_OVERRIDE {
         return true;
     }
diff --git a/src/gpu/GrXferProcessor.cpp b/src/gpu/GrXferProcessor.cpp
index 358a249060..321dcfd5e8 100644
--- a/src/gpu/GrXferProcessor.cpp
+++ b/src/gpu/GrXferProcessor.cpp
@@ -38,7 +38,7 @@ GrXferProcessor* GrXPFactory::createXferProcessor(const GrProcOptInfo& colorPOI,
                                                   const GrDeviceCoordTexture* dstCopy,
                                                   const GrDrawTargetCaps& caps) const {
 #ifdef SK_DEBUG
-    if (this->willReadDstColor(caps, colorPOI, coveragePOI)) {
+    if (this->willReadDstColor(colorPOI, coveragePOI)) {
         if (!caps.dstReadInShaderSupport()) {
             SkASSERT(dstCopy && dstCopy->texture());
         } else {
@@ -46,13 +46,14 @@ GrXferProcessor* GrXPFactory::createXferProcessor(const GrProcOptInfo& colorPOI,
         }
     } else {
         SkASSERT(!dstCopy || !dstCopy->texture()); 
+
     }
 #endif
-    return this->onCreateXferProcessor(caps, colorPOI, coveragePOI, dstCopy);
+    return this->onCreateXferProcessor(colorPOI, coveragePOI, dstCopy);
 }
 
 bool GrXPFactory::willNeedDstCopy(const GrDrawTargetCaps& caps, const GrProcOptInfo& colorPOI,
                                   const GrProcOptInfo& coveragePOI) const {
-    return (this->willReadDstColor(caps, colorPOI, coveragePOI) && !caps.dstReadInShaderSupport());
+    return (this->willReadDstColor(colorPOI, coveragePOI) && !caps.dstReadInShaderSupport());
 }
 
diff --git a/src/gpu/effects/GrCoverageSetOpXP.cpp b/src/gpu/effects/GrCoverageSetOpXP.cpp
index 40998d5033..f0ec1f9b00 100644
--- a/src/gpu/effects/GrCoverageSetOpXP.cpp
+++ b/src/gpu/effects/GrCoverageSetOpXP.cpp
@@ -228,8 +228,7 @@ GrXPFactory* GrCoverageSetOpXPFactory::Create(SkRegion::Op regionOp, bool invert
 }
 
 GrXferProcessor*
-GrCoverageSetOpXPFactory::onCreateXferProcessor(const GrDrawTargetCaps& caps,
-                                                const GrProcOptInfo& colorPOI,
+GrCoverageSetOpXPFactory::onCreateXferProcessor(const GrProcOptInfo& colorPOI,
                                                 const GrProcOptInfo& covPOI,
                                                 const GrDeviceCoordTexture* dstCopy) const {
     return CoverageSetOpXP::Create(fRegionOp, fInvertCoverage);
diff --git a/src/gpu/effects/GrCoverageSetOpXP.h b/src/gpu/effects/GrCoverageSetOpXP.h
index e8900b3604..01dce95211 100644
--- a/src/gpu/effects/GrCoverageSetOpXP.h
+++ b/src/gpu/effects/GrCoverageSetOpXP.h
@@ -35,13 +35,11 @@ public:
 private:
     GrCoverageSetOpXPFactory(SkRegion::Op regionOp, bool invertCoverage);
 
-    GrXferProcessor* onCreateXferProcessor(const GrDrawTargetCaps& caps,
-                                           const GrProcOptInfo& colorPOI,
+    GrXferProcessor* onCreateXferProcessor(const GrProcOptInfo& colorPOI,
                                            const GrProcOptInfo& coveragePOI,
                                            const GrDeviceCoordTexture* dstCopy) const SK_OVERRIDE;
 
-    bool willReadDstColor(const GrDrawTargetCaps& caps,
-                          const GrProcOptInfo& colorPOI,
+    bool willReadDstColor(const GrProcOptInfo& colorPOI,
                           const GrProcOptInfo& coveragePOI) const SK_OVERRIDE {
         return false;
     }
diff --git a/src/gpu/effects/GrCustomXfermode.cpp b/src/gpu/effects/GrCustomXfermode.cpp
index e4d65e41e4..8d8f9f251d 100644
--- a/src/gpu/effects/GrCustomXfermode.cpp
+++ b/src/gpu/effects/GrCustomXfermode.cpp
@@ -608,11 +608,10 @@ GrCustomXPFactory::GrCustomXPFactory(SkXfermode::Mode mode)
 }
 
 GrXferProcessor*
-GrCustomXPFactory::onCreateXferProcessor(const GrDrawTargetCaps& caps,
-                                         const GrProcOptInfo& colorPOI,
+GrCustomXPFactory::onCreateXferProcessor(const GrProcOptInfo& colorPOI,
                                          const GrProcOptInfo& coveragePOI,
                                          const GrDeviceCoordTexture* dstCopy) const {
-    return CustomXP::Create(fMode, dstCopy, this->willReadDstColor(caps, colorPOI, coveragePOI));
+    return CustomXP::Create(fMode, dstCopy, this->willReadDstColor(colorPOI, coveragePOI));
 }
 
 
diff --git a/src/gpu/effects/GrCustomXfermodePriv.h b/src/gpu/effects/GrCustomXfermodePriv.h
index 8672529e45..959b079603 100644
--- a/src/gpu/effects/GrCustomXfermodePriv.h
+++ b/src/gpu/effects/GrCustomXfermodePriv.h
@@ -77,13 +77,11 @@ public:
                             GrXPFactory::InvariantOutput*) const SK_OVERRIDE;
 
 private:
-    GrXferProcessor* onCreateXferProcessor(const GrDrawTargetCaps& caps,
-                                           const GrProcOptInfo& colorPOI,
+    GrXferProcessor* onCreateXferProcessor(const GrProcOptInfo& colorPOI,
                                            const GrProcOptInfo& coveragePOI,
                                            const GrDeviceCoordTexture* dstCopy) const SK_OVERRIDE; 
 
-    bool willReadDstColor(const GrDrawTargetCaps& caps,
-                          const GrProcOptInfo& colorPOI,
+    bool willReadDstColor(const GrProcOptInfo& colorPOI,
                           const GrProcOptInfo& coveragePOI) const SK_OVERRIDE {
         return true;
     }
diff --git a/src/gpu/effects/GrDisableColorXP.cpp b/src/gpu/effects/GrDisableColorXP.cpp
index d97589dcb6..637f99baf1 100644
--- a/src/gpu/effects/GrDisableColorXP.cpp
+++ b/src/gpu/effects/GrDisableColorXP.cpp
@@ -100,8 +100,7 @@ GrDisableColorXPFactory::GrDisableColorXPFactory() {
 }
 
 GrXferProcessor*
-GrDisableColorXPFactory::onCreateXferProcessor(const GrDrawTargetCaps& caps,
-                                               const GrProcOptInfo& colorPOI,
+GrDisableColorXPFactory::onCreateXferProcessor(const GrProcOptInfo& colorPOI,
                                                const GrProcOptInfo& covPOI,
                                                const GrDeviceCoordTexture* dstCopy) const {
     return DisableColorXP::Create();
diff --git a/src/gpu/effects/GrDisableColorXP.h b/src/gpu/effects/GrDisableColorXP.h
index 00675884a9..fe60b595a0 100644
--- a/src/gpu/effects/GrDisableColorXP.h
+++ b/src/gpu/effects/GrDisableColorXP.h
@@ -39,13 +39,11 @@ public:
 private:
     GrDisableColorXPFactory();
 
-    GrXferProcessor* onCreateXferProcessor(const GrDrawTargetCaps& caps,
-                                           const GrProcOptInfo& colorPOI,
+    GrXferProcessor* onCreateXferProcessor(const GrProcOptInfo& colorPOI,
                                            const GrProcOptInfo& coveragePOI,
                                            const GrDeviceCoordTexture* dstCopy) const SK_OVERRIDE;
 
-    bool willReadDstColor(const GrDrawTargetCaps& caps,
-                          const GrProcOptInfo& colorPOI,
+    bool willReadDstColor(const GrProcOptInfo& colorPOI,
                           const GrProcOptInfo& coveragePOI) const SK_OVERRIDE {
         return false;
     }
diff --git a/src/gpu/effects/GrPorterDuffXferProcessor.cpp b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
index 22029e1d14..6f2b63f5cb 100644
--- a/src/gpu/effects/GrPorterDuffXferProcessor.cpp
+++ b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
@@ -59,10 +59,6 @@ public:
         kCoverage_PrimaryOutputType,
         // Modulate color and coverage, write result as the color output.
         kModulate_PrimaryOutputType,
-        // Custom Porter-Duff output, used for when we explictly are reading the dst and blending
-        // in the shader. Secondary Output must be none if you use this. The custom blend uses the
-        // equation: cov * (coeffS * S + coeffD * D) + (1 - cov) * D
-        kCustom_PrimaryOutputType
     };
 
     enum SecondaryOutputType {
@@ -91,19 +87,11 @@ public:
                                                const GrDrawTargetCaps& caps) SK_OVERRIDE;
 
     void getBlendInfo(GrXferProcessor::BlendInfo* blendInfo) const SK_OVERRIDE {
-        if (!this->willReadDstColor()) {
-            blendInfo->fSrcBlend = fSrcBlend;
-            blendInfo->fDstBlend = fDstBlend;
-        } else {
-            blendInfo->fSrcBlend = kOne_GrBlendCoeff;
-            blendInfo->fDstBlend = kZero_GrBlendCoeff;
-        }
+        blendInfo->fSrcBlend = fSrcBlend;
+        blendInfo->fDstBlend = fDstBlend;
         blendInfo->fBlendConstant = fBlendConstant;
     }
 
-    GrBlendCoeff getSrcBlend() const { return fSrcBlend; }
-    GrBlendCoeff getDstBlend() const { return fDstBlend; }
-
 private:
     PorterDuffXferProcessor(GrBlendCoeff srcBlend, GrBlendCoeff dstBlend, GrColor constant,
                             const GrDeviceCoordTexture* dstCopy, bool willReadDstColor);
@@ -140,50 +128,6 @@ private:
 
 ///////////////////////////////////////////////////////////////////////////////
 
-bool append_porterduff_term(GrGLFPFragmentBuilder* fsBuilder, GrBlendCoeff coeff,
-                            const char* colorName, const char* srcColorName,
-                            const char* dstColorName, bool hasPrevious) {
-    if (kZero_GrBlendCoeff == coeff) {
-        return hasPrevious;
-    } else {
-        if (hasPrevious) {
-            fsBuilder->codeAppend(" + ");
-        }
-        fsBuilder->codeAppendf("%s", colorName);
-        switch (coeff) {
-            case kOne_GrBlendCoeff:
-                break;
-            case kSC_GrBlendCoeff:
-                fsBuilder->codeAppendf(" * %s", srcColorName); 
-                break;
-            case kISC_GrBlendCoeff:
-                fsBuilder->codeAppendf(" * (vec4(1.0) - %s)", srcColorName); 
-                break;
-            case kDC_GrBlendCoeff:
-                fsBuilder->codeAppendf(" * %s", dstColorName); 
-                break;
-            case kIDC_GrBlendCoeff:
-                fsBuilder->codeAppendf(" * (vec4(1.0) - %s)", dstColorName); 
-                break;
-            case kSA_GrBlendCoeff:
-                fsBuilder->codeAppendf(" * %s.a", srcColorName); 
-                break;
-            case kISA_GrBlendCoeff:
-                fsBuilder->codeAppendf(" * (1.0 - %s.a)", srcColorName); 
-                break;
-            case kDA_GrBlendCoeff:
-                fsBuilder->codeAppendf(" * %s.a", dstColorName); 
-                break;
-            case kIDA_GrBlendCoeff:
-                fsBuilder->codeAppendf(" * (1.0 - %s.a)", dstColorName); 
-                break;
-            default:
-                SkFAIL("Unsupported Blend Coeff");
-        }
-        return true;
-    }
-}
-
 class GLPorterDuffXferProcessor : public GrGLXferProcessor {
 public:
     GLPorterDuffXferProcessor(const GrProcessor&) {}
@@ -195,24 +139,16 @@ public:
         const PorterDuffXferProcessor& xp = processor.cast<PorterDuffXferProcessor>();
         b->add32(xp.primaryOutputType());
         b->add32(xp.secondaryOutputType());
-        if (xp.willReadDstColor()) {
-            b->add32(xp.getSrcBlend());
-            b->add32(xp.getDstBlend());
-        }
     };
 
 private:
     void onEmitCode(const EmitArgs& args) SK_OVERRIDE {
         const PorterDuffXferProcessor& xp = args.fXP.cast<PorterDuffXferProcessor>();
         GrGLFPFragmentBuilder* fsBuilder = args.fPB->getFragmentShaderBuilder();
-        if (PorterDuffXferProcessor::kCustom_PrimaryOutputType != xp.primaryOutputType()) {
-            SkASSERT(!xp.willReadDstColor());
+        if (xp.hasSecondaryOutput()) {
             switch(xp.secondaryOutputType()) {
-                case PorterDuffXferProcessor::kNone_SecondaryOutputType:
-                    break;
                 case PorterDuffXferProcessor::kCoverage_SecondaryOutputType:
-                    fsBuilder->codeAppendf("%s = %s;", args.fOutputSecondary,
-                                           args.fInputCoverage);
+                    fsBuilder->codeAppendf("%s = %s;", args.fOutputSecondary, args.fInputCoverage);
                     break;
                 case PorterDuffXferProcessor::kCoverageISA_SecondaryOutputType:
                     fsBuilder->codeAppendf("%s = (1.0 - %s.a) * %s;",
@@ -227,43 +163,24 @@ private:
                 default:
                     SkFAIL("Unexpected Secondary Output");
             }
-
-            switch (xp.primaryOutputType()) {
-                case PorterDuffXferProcessor::kNone_PrimaryOutputType:
-                    fsBuilder->codeAppendf("%s = vec4(0);", args.fOutputPrimary);
-                    break;
-                case PorterDuffXferProcessor::kColor_PrimaryOutputType:
-                    fsBuilder->codeAppendf("%s = %s;", args.fOutputPrimary, args.fInputColor);
-                    break;
-                case PorterDuffXferProcessor::kCoverage_PrimaryOutputType:
-                    fsBuilder->codeAppendf("%s = %s;", args.fOutputPrimary, args.fInputCoverage);
-                    break;
-                case PorterDuffXferProcessor::kModulate_PrimaryOutputType:
-                    fsBuilder->codeAppendf("%s = %s * %s;", args.fOutputPrimary, args.fInputColor,
-                                           args.fInputCoverage);
-                    break;
-                default:
-                    SkFAIL("Unexpected Primary Output");
-            }
-        } else {
-            SkASSERT(xp.willReadDstColor());
-
-            const char* dstColor = fsBuilder->dstColor();
-
-            fsBuilder->codeAppend("vec4 colorBlend =");
-            // append src blend
-            bool didAppend = append_porterduff_term(fsBuilder, xp.getSrcBlend(),
-                                                    args.fInputColor, args.fInputColor,
-                                                    dstColor, false);
-            // append dst blend
-            SkAssertResult(append_porterduff_term(fsBuilder, xp.getDstBlend(),
-                                                  dstColor, args.fInputColor,
-                                                  dstColor, didAppend));
-            fsBuilder->codeAppend(";");
-
-            fsBuilder->codeAppendf("%s = %s * colorBlend + (vec4(1.0) - %s) * %s;",
-                                   args.fOutputPrimary, args.fInputCoverage, args.fInputCoverage,
-                                   dstColor);
+        }
+        
+        switch (xp.primaryOutputType()) {
+            case PorterDuffXferProcessor::kNone_PrimaryOutputType:
+                fsBuilder->codeAppendf("%s = vec4(0);", args.fOutputPrimary);
+                break;
+            case PorterDuffXferProcessor::kColor_PrimaryOutputType:
+                fsBuilder->codeAppendf("%s = %s;", args.fOutputPrimary, args.fInputColor);
+                break;
+            case PorterDuffXferProcessor::kCoverage_PrimaryOutputType:
+                fsBuilder->codeAppendf("%s = %s;", args.fOutputPrimary, args.fInputCoverage);
+                break;
+            case PorterDuffXferProcessor::kModulate_PrimaryOutputType:
+                fsBuilder->codeAppendf("%s = %s * %s;", args.fOutputPrimary, args.fInputColor,
+                                       args.fInputCoverage);
+                break;
+            default:
+                SkFAIL("Unexpected Primary Output");
         }
     }
 
@@ -279,8 +196,7 @@ PorterDuffXferProcessor::PorterDuffXferProcessor(GrBlendCoeff srcBlend,
                                                  GrColor constant,
                                                  const GrDeviceCoordTexture* dstCopy,
                                                  bool willReadDstColor)
-    : INHERITED(dstCopy, willReadDstColor)
-    , fSrcBlend(srcBlend)
+    : fSrcBlend(srcBlend)
     , fDstBlend(dstBlend)
     , fBlendConstant(constant)
     , fPrimaryOutputType(kModulate_PrimaryOutputType) 
@@ -328,11 +244,6 @@ PorterDuffXferProcessor::getOptimizations(const GrProcOptInfo& colorPOI,
 void PorterDuffXferProcessor::calcOutputTypes(GrXferProcessor::OptFlags optFlags,
                                               const GrDrawTargetCaps& caps,
                                               bool hasSolidCoverage) {
-    if (this->willReadDstColor()) {
-        fPrimaryOutputType = kCustom_PrimaryOutputType;
-        return;
-    }
-
     if (optFlags & kIgnoreColor_OptFlag) {
         if (optFlags & kIgnoreCoverage_OptFlag) {
             fPrimaryOutputType = kNone_PrimaryOutputType;
@@ -373,12 +284,11 @@ GrXferProcessor::OptFlags
 PorterDuffXferProcessor::internalGetOptimizations(const GrProcOptInfo& colorPOI,
                                                   const GrProcOptInfo& coveragePOI,
                                                   bool doesStencilWrite) {
-    if (this->willReadDstColor()) {
-        return GrXferProcessor::kNone_Opt;
-    }
+    bool srcAIsOne;
+    bool hasCoverage;
 
-    bool srcAIsOne = colorPOI.isOpaque();
-    bool hasCoverage = !coveragePOI.isSolidWhite();
+    srcAIsOne = colorPOI.isOpaque();
+    hasCoverage = !coveragePOI.isSolidWhite();
 
     bool dstCoeffIsOne = kOne_GrBlendCoeff == fDstBlend ||
                          (kSA_GrBlendCoeff == fDstBlend && srcAIsOne);
@@ -543,20 +453,19 @@ GrXPFactory* GrPorterDuffXPFactory::Create(SkXfermode::Mode mode) {
 }
 
 GrXferProcessor*
-GrPorterDuffXPFactory::onCreateXferProcessor(const GrDrawTargetCaps& caps,
-                                             const GrProcOptInfo& colorPOI,
+GrPorterDuffXPFactory::onCreateXferProcessor(const GrProcOptInfo& colorPOI,
                                              const GrProcOptInfo& covPOI,
                                              const GrDeviceCoordTexture* dstCopy) const {
     if (!covPOI.isFourChannelOutput()) {
         return PorterDuffXferProcessor::Create(fSrcCoeff, fDstCoeff, 0, dstCopy,
-                                               this->willReadDstColor(caps, colorPOI, covPOI));
+                                               this->willReadDstColor(colorPOI, covPOI));
     } else {
         if (this->supportsRGBCoverage(colorPOI.color(), colorPOI.validFlags())) {
             SkASSERT(kRGBA_GrColorComponentFlags == colorPOI.validFlags());
             GrColor blendConstant = GrUnPreMulColor(colorPOI.color());
             return PorterDuffXferProcessor::Create(kConstC_GrBlendCoeff, kISC_GrBlendCoeff,
                                                    blendConstant, dstCopy,
-                                                   this->willReadDstColor(caps, colorPOI, covPOI));
+                                                   this->willReadDstColor(colorPOI, covPOI));
         } else {
             return NULL;
         }
@@ -572,6 +481,39 @@ bool GrPorterDuffXPFactory::supportsRGBCoverage(GrColor /*knownColor*/,
     return false;
 }
 
+bool GrPorterDuffXPFactory::canApplyCoverage(const GrProcOptInfo& colorPOI,
+                                             const GrProcOptInfo& coveragePOI) const {
+    bool srcAIsOne = colorPOI.isOpaque();
+
+    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.
+    // check whether coverage can be safely rolled into alpha
+    // of if we can skip color computation and just emit coverage
+    if (this->canTweakAlphaForCoverage()) {
+        return true;
+    }
+    if (dstCoeffIsZero) {
+        if (kZero_GrBlendCoeff == fSrcCoeff) {
+            return true;
+        } else if (srcAIsOne) {
+            return  true;
+        }
+    } else if (dstCoeffIsOne) {
+        return true;
+    }
+
+    return false;
+}
+
 bool GrPorterDuffXPFactory::canTweakAlphaForCoverage() const {
     return can_tweak_alpha_for_coverage(fDstCoeff);
 }
@@ -645,37 +587,9 @@ void GrPorterDuffXPFactory::getInvariantOutput(const GrProcOptInfo& colorPOI,
     output->fWillBlendWithDst = false;
 }
 
-bool GrPorterDuffXPFactory::willReadDstColor(const GrDrawTargetCaps& caps,
-                                             const GrProcOptInfo& colorPOI,
+bool GrPorterDuffXPFactory::willReadDstColor(const GrProcOptInfo& colorPOI,
                                              const GrProcOptInfo& coveragePOI) const {
-    // We can always blend correctly if we have dual source blending.
-    if (caps.dualSourceBlendingSupport()) {
-        return false;
-    }
-
-    if (this->canTweakAlphaForCoverage()) {
-        return false;
-    }
-
-    bool srcAIsOne = colorPOI.isOpaque();
-
-    if (kZero_GrBlendCoeff == fDstCoeff) {
-        if (kZero_GrBlendCoeff == fSrcCoeff || srcAIsOne) {
-            return false;
-        }
-    }
-
-    // Reduces to: coeffS * (Cov*S) + D
-    if (kSA_GrBlendCoeff == fDstCoeff && srcAIsOne) {
-        return false;
-    }
-
-    // We can always blend correctly if we have solid coverage.
-    if (coveragePOI.isSolidWhite()) {
-        return false;
-    }
-
-    return true;
+    return false;
 }
 
 GR_DEFINE_XP_FACTORY_TEST(GrPorterDuffXPFactory);