Implement the clip as 4 or fewer GrEffects when possible.

src/gpu/effects/GrConvexPolyEffect.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrConvexPolyEffect.h"
 
 #include "gl/GrGLEffect.h"
@@ skipping 125 matching lines @@
         builder->fsCodeAppendf("\t\txSub += min(%s.z - %s.x, 0.0);\n", rectName, fragmentPos);
         builder->fsCodeAppendf("\t\tySub = min(%s.y - %s.y, 0.0);\n", fragmentPos, rectName);
         builder->fsCodeAppendf("\t\tySub += min(%s.w - %s.y, 0.0);\n", rectName, fragmentPos);
         // Now compute coverage in x and y and multiply them to get the fraction of the pixel
         // covered.
         builder->fsCodeAppendf("\t\tfloat alpha = (1.0 + max(xSub, -1.0)) * (1.0 + max(ySub, -1.0));\n");
     } else {
         builder->fsCodeAppendf("\t\tfloat alpha = 1.0;\n");
         builder->fsCodeAppendf("\t\talpha *= (%s.x - %s.x) > -0.5 ? 1.0 : 0.0;\n", fragmentPos, rectName);
         builder->fsCodeAppendf("\t\talpha *= (%s.z - %s.x) > -0.5 ? 1.0 : 0.0;\n", rectName, fragmentPos);
-        builder->fsCodeAppendf("\t\talpha *= (%s.y - %s.y) > 0.5 ? 1.0 : 0.0;\n", fragmentPos, rectName);
-        builder->fsCodeAppendf("\t\talpha *= (%s.w - %s.y) > 0.5 ? 1.0 : 0.0;\n", rectName, fragmentPos);
+        builder->fsCodeAppendf("\t\talpha *= (%s.y - %s.y) > -0.5 ? 1.0 : 0.0;\n", fragmentPos, rectName);
+        builder->fsCodeAppendf("\t\talpha *= (%s.w - %s.y) > -0.5 ? 1.0 : 0.0;\n", rectName, fragmentPos);
     }
 
     if (GrEffectEdgeTypeIsInverseFill(aare.getEdgeType())) {
         builder->fsCodeAppend("\t\talpha = 1.0 - alpha;\n");
     }
     builder->fsCodeAppendf("\t\t%s = %s;\n", outputColor,
                            (GrGLSLExpr4(inputColor) * GrGLSLExpr1("alpha")).c_str());
 }
 
 void GLAARectEffect::setData(const GrGLUniformManager& uman, const GrDrawEffect& drawEffect) {
@@ skipping 207 matching lines @@
     }
 
     GrEffectRef* effect;
     do {
         GrEffectEdgeType edgeType = static_cast<GrEffectEdgeType>(
                                         random->nextULessThan(kGrEffectEdgeTypeCnt));
         effect = GrConvexPolyEffect::Create(edgeType, count, edges);
     } while (NULL == effect);
     return effect;
 }