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();

[Chris Dalton, 2014/11/12 21:21:48]

Just a thought, I'm not too familiar with how slow a call can be to
srcAlphaWillBeOne, but if it's slow enough it may be worth it to only call if
needed -- only when src coefficient is ISA, we know the dst coefficient doesn't
ref the dst, etc. etc. etc.

     GrBlendCoeff srcCoeff = this->getSrcBlendCoeff();
     GrBlendCoeff dstCoeff = this->getDstBlendCoeff();
     if (kISA_GrBlendCoeff == dstCoeff && srcAIsOne) {

[bsalomon, 2014/11/12 21:33:38]

At a minimum we can just change this srcAIsOne to this->srcAlphaWillBeOne() and
remove the above line so that it isn't called unless dstCoeff is kISA.

Otherwise, lgtm.

         dstCoeff = kZero_GrBlendCoeff;
     }
-    if (kOne_GrBlendCoeff != srcCoeff ||
+    if (GrBlendCoeffRefsDst(srcCoeff) ||
         kZero_GrBlendCoeff != dstCoeff ||
         this->willEffectReadDstColor()) {
         return true;
     }
 
     return false;
 }