Relax constraints on src coeff in GrDrawState::willBlendWithDst.

src/gpu/GrDrawState.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrDrawState.h"
 
+#include "GrBlend.h"
 #include "GrInvariantOutput.h"
 #include "GrOptDrawState.h"
 #include "GrPaint.h"
 
 //////////////////////////////////////////////////////////////////////////////s
 
 bool GrDrawState::isEqual(const GrDrawState& that) const {
     bool usingVertexColors = this->hasColorVertexAttribute();
     if (!usingVertexColors && this->fColor != that.fColor) {
         return false;
@@ skipping 722 matching lines @@
     }
 
     return inoutColor.isOpaque();
 }
 
 bool GrDrawState::willBlendWithDst() const {
     if (!this->hasSolidCoverage()) {
         return true;
     }
 
-    bool srcAIsOne = this->srcAlphaWillBeOne();
-    GrBlendCoeff srcCoeff = this->getSrcBlendCoeff();
-    GrBlendCoeff dstCoeff = this->getDstBlendCoeff();
-    if (kISA_GrBlendCoeff == dstCoeff && srcAIsOne) {
-        dstCoeff = kZero_GrBlendCoeff;
-    }
-    if (kOne_GrBlendCoeff != srcCoeff ||
-        kZero_GrBlendCoeff != dstCoeff ||
-        this->willEffectReadDstColor()) {
+    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;
 }