Use stencil ops that don't issue writes whenever possible

src/gpu/GrStencilAndCoverPathRenderer.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 "GrStencilAndCoverPathRenderer.h"
@@ skipping 84 matching lines @@
 
     if (args.fAntiAlias) {
         SkASSERT(pipelineBuilder->getRenderTarget()->isStencilBufferMultisampled());
         pipelineBuilder->enableState(GrPipelineBuilder::kHWAntialias_Flag);
     }
 
     SkAutoTUnref<GrPath> p(get_gr_path(fResourceProvider, path, *args.fStroke));
 
     if (path.isInverseFillType()) {
         GR_STATIC_CONST_SAME_STENCIL(kInvertedStencilPass,
-            kZero_StencilOp,
+            kKeep_StencilOp,
             kZero_StencilOp,
             // We know our rect will hit pixels outside the clip and the user bits will be 0
             // outside the clip. So we can't just fill where the user bits are 0. We also need to
             // check that the clip bit is set.
             kEqualIfInClip_StencilFunc,
             0xffff,
             0x0000,
             0xffff);
 
         pipelineBuilder->setStencil(kInvertedStencilPass);
@@ skipping 18 matching lines @@
         } else {
             if (!viewMatrix.invert(&invert)) {
                 return false;
             }
         }
         const SkMatrix& viewM = viewMatrix.hasPerspective() ? SkMatrix::I() : viewMatrix;
         args.fTarget->drawBWRect(*pipelineBuilder, args.fColor, viewM, bounds, NULL, &invert);
     } else {
         GR_STATIC_CONST_SAME_STENCIL(kStencilPass,
             kZero_StencilOp,
-            kZero_StencilOp,
+            kKeep_StencilOp,
             kNotEqual_StencilFunc,
             0xffff,
             0x0000,
             0xffff);
 
         pipelineBuilder->setStencil(kStencilPass);
         SkAutoTUnref<GrPathProcessor> pp(GrPathProcessor::Create(args.fColor, viewMatrix));
         args.fTarget->drawPath(*pipelineBuilder, pp, p,
                                convert_skpath_filltype(path.getFillType()));
     }
 
     pipelineBuilder->stencil()->setDisabled();
     return true;
 }