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

src/gpu/GrDrawState.cpp

Index: src/gpu/GrDrawState.cpp
diff --git a/src/gpu/GrDrawState.cpp b/src/gpu/GrDrawState.cpp
index 51ef6cf5d3c8302c815aacb2ba356278c35c25f5..8c2d75f0b502715d2d8d0e25411b08530d1b4671 100644
--- a/src/gpu/GrDrawState.cpp
+++ b/src/gpu/GrDrawState.cpp
@@ -14,6 +14,8 @@
 #include "GrXferProcessor.h"
 #include "effects/GrPorterDuffXferProcessor.h"
 
+///////////////////////////////////////////////////////////////////////////////
+
 bool GrDrawState::isEqual(const GrDrawState& that) const {
     bool usingVertexColors = this->hasColorVertexAttribute();
     if (!usingVertexColors && this->fColor != that.fColor) {
@@ -24,6 +26,9 @@
         this->fColorStages.count() != that.fColorStages.count() ||
         this->fCoverageStages.count() != that.fCoverageStages.count() ||
         !this->fViewMatrix.cheapEqualTo(that.fViewMatrix) ||
+        this->fSrcBlend != that.fSrcBlend ||
+        this->fDstBlend != that.fDstBlend ||
+        this->fBlendConstant != that.fBlendConstant ||
         this->fFlagBits != that.fFlagBits ||
         this->fStencilSettings != that.fStencilSettings ||
         this->fDrawFace != that.fDrawFace) {
@@ -85,6 +90,9 @@
     fRenderTarget.reset(SkSafeRef(that.fRenderTarget.get()));
     fColor = that.fColor;
     fViewMatrix = that.fViewMatrix;
+    fSrcBlend = that.fSrcBlend;
+    fDstBlend = that.fDstBlend;
+    fBlendConstant = that.fBlendConstant;
     fFlagBits = that.fFlagBits;
     fStencilSettings = that.fStencilSettings;
     fCoverage = that.fCoverage;
@@ -122,6 +130,9 @@
     } else {
         fViewMatrix = *initialViewMatrix;
     }
+    fSrcBlend = kOne_GrBlendCoeff;
+    fDstBlend = kZero_GrBlendCoeff;
+    fBlendConstant = 0x0;
     fFlagBits = 0x0;
     fStencilSettings.setDisabled();
     fCoverage = 0xff;
@@ -168,11 +179,13 @@
 
     fXPFactory.reset(SkRef(paint.getXPFactory()));
 
+    this->setBlendFunc(paint.getSrcBlendCoeff(), paint.getDstBlendCoeff());
     this->setRenderTarget(rt);
 
     fViewMatrix = vm;
 
     // These have no equivalent in GrPaint, set them to defaults
+    fBlendConstant = 0x0;
     fDrawFace = kBoth_DrawFace;
     fStencilSettings.setDisabled();
     fFlagBits = 0;
@@ -196,11 +209,15 @@
     if (caps.dualSourceBlendingSupport()) {
         return true;
     }
-
-    this->calcColorInvariantOutput();
-    this->calcCoverageInvariantOutput();
-    return fXPFactory->canApplyCoverage(fColorProcInfo, fCoverageProcInfo,
-                                        this->isCoverageDrawing(), this->isColorWriteDisabled());
+    // we can correctly apply coverage if a) we have dual source blending
+    // or b) one of our blend optimizations applies
+    // or c) the src, dst blend coeffs are 1,0 and we will read Dst Color
+    GrBlendCoeff srcCoeff;
+    GrBlendCoeff dstCoeff;
+    BlendOpt opt = this->getBlendOpt(true, &srcCoeff, &dstCoeff);
+    return GrDrawState::kNone_BlendOpt != opt ||
+           (this->willEffectReadDstColor() &&
+            kOne_GrBlendCoeff == srcCoeff && kZero_GrBlendCoeff == dstCoeff);
 }
 
 bool GrDrawState::hasSolidCoverage() const {
@@ -220,22 +237,13 @@
 //////////////////////////////////////////////////////////////////////////////s
 
 bool GrDrawState::willEffectReadDstColor() const {
-    this->calcColorInvariantOutput();
-    this->calcCoverageInvariantOutput();
-    // TODO: Remove need to create the XP here.
-    //       Also once all custom blends are turned into XPs we can remove the need
-    //       to check other stages since only xp's will be able to read dst
-    SkAutoTUnref<GrXferProcessor> xferProcessor(fXPFactory->createXferProcessor(fColorProcInfo,
-                                                                                fCoverageProcInfo));
-    if (xferProcessor && xferProcessor->willReadDstColor()) {
-        return true;
-    }
-
     if (!this->isColorWriteDisabled()) {
+        this->calcColorInvariantOutput();
         if (fColorProcInfo.readsDst()) {
             return true;
         }
     }
+    this->calcCoverageInvariantOutput();
     return fCoverageProcInfo.readsDst();
 }
 
@@ -280,7 +288,21 @@
 // Some blend modes allow folding a fractional coverage value into the color's alpha channel, while
 // others will blend incorrectly.
 bool GrDrawState::canTweakAlphaForCoverage() const {
-    return fXPFactory->canTweakAlphaForCoverage(this->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.
+     */
+    return kOne_GrBlendCoeff == fDstBlend ||
+           kISA_GrBlendCoeff == fDstBlend ||
+           kISC_GrBlendCoeff == fDstBlend ||
+           this->isCoverageDrawing();
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -378,6 +400,97 @@
 
 ////////////////////////////////////////////////////////////////////////////////
 
+GrDrawState::BlendOpt GrDrawState::getBlendOpt(bool forceCoverage,
+                                               GrBlendCoeff* srcCoeff,
+                                               GrBlendCoeff* dstCoeff) const {
+    GrBlendCoeff bogusSrcCoeff, bogusDstCoeff;
+    if (NULL == srcCoeff) {
+        srcCoeff = &bogusSrcCoeff;
+    }
+    if (NULL == dstCoeff) {
+        dstCoeff = &bogusDstCoeff;
+    }
+
+    *srcCoeff = this->getSrcBlendCoeff();
+    *dstCoeff = this->getDstBlendCoeff();
+
+    if (this->isColorWriteDisabled()) {
+        *srcCoeff = kZero_GrBlendCoeff;
+        *dstCoeff = kOne_GrBlendCoeff;
+    }
+
+    bool srcAIsOne = this->srcAlphaWillBeOne();
+    bool dstCoeffIsOne = kOne_GrBlendCoeff == *dstCoeff ||
+                         (kSA_GrBlendCoeff == *dstCoeff && srcAIsOne);
+    bool dstCoeffIsZero = kZero_GrBlendCoeff == *dstCoeff ||
+                         (kISA_GrBlendCoeff == *dstCoeff && srcAIsOne);
+
+    // 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 == *srcCoeff && dstCoeffIsOne)) {
+        if (this->getStencil().doesWrite()) {
+            return kEmitCoverage_BlendOpt;
+        } else {
+            *dstCoeff = kOne_GrBlendCoeff;
+            return kSkipDraw_BlendOpt;
+        }
+    }
+
+    bool hasCoverage = forceCoverage || !this->hasSolidCoverage();
+
+    // 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 == *srcCoeff) {
+                // 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
+                *dstCoeff = kZero_GrBlendCoeff;
+                return kNone_BlendOpt;
+            } else if (kZero_GrBlendCoeff == *srcCoeff) {
+                // if the op is "clear" then we don't need to emit a color
+                // or blend, just write transparent black into the dst.
+                *srcCoeff = kOne_GrBlendCoeff;
+                *dstCoeff = kZero_GrBlendCoeff;
+                return kEmitTransBlack_BlendOpt;
+            }
+        }
+    } else if (this->isCoverageDrawing()) {
+        // we have coverage but we aren't distinguishing it from alpha by request.
+        return kCoverageAsAlpha_BlendOpt;
+    } else {
+        // check whether coverage can be safely rolled into alpha
+        // of if we can skip color computation and just emit coverage
+        if (this->canTweakAlphaForCoverage()) {
+            return kCoverageAsAlpha_BlendOpt;
+        }
+        if (dstCoeffIsZero) {
+            if (kZero_GrBlendCoeff == *srcCoeff) {
+                // 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.
+                *dstCoeff = kISA_GrBlendCoeff;
+                return  kEmitCoverage_BlendOpt;
+            } 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.
+                *dstCoeff = kISA_GrBlendCoeff;
+                return  kCoverageAsAlpha_BlendOpt;
+            }
+        } else if (dstCoeffIsOne) {
+            // the dst coeff is effectively one so blend works out to:
+            // cS + (c)(1)D + (1-c)D = cS + D.
+            *dstCoeff = kOne_GrBlendCoeff;
+            return  kCoverageAsAlpha_BlendOpt;
+        }
+    }
+
+    return kNone_BlendOpt;
+}
+
 bool GrDrawState::srcAlphaWillBeOne() const {
     this->calcColorInvariantOutput();
     if (this->isCoverageDrawing()) {
@@ -388,10 +501,25 @@
 }
 
 bool GrDrawState::willBlendWithDst() const {
-    this->calcColorInvariantOutput();
-    this->calcCoverageInvariantOutput();
-    return fXPFactory->willBlendWithDst(fColorProcInfo, fCoverageProcInfo,
-                                        this->isCoverageDrawing(), this->isColorWriteDisabled());
+    if (!this->hasSolidCoverage()) {
+        return true;
+    }
+
+    if (this->willEffectReadDstColor()) {
+        return true;
+    }
+
+    if (GrBlendCoeffRefsDst(this->getSrcBlendCoeff())) {
+        return true;
+    }
+
+    GrBlendCoeff dstCoeff = this->getDstBlendCoeff();
+    if (!(kZero_GrBlendCoeff == dstCoeff ||
+         (kISA_GrBlendCoeff == dstCoeff && this->srcAlphaWillBeOne()))) {
+        return true;
+    }
+
+    return false;
 }
 
 void GrDrawState::calcColorInvariantOutput() const {
@@ -433,3 +561,4 @@
         fCoverageProcInfoValid = true;
     }
 }
+