On gpu, use max(r,g,b) for coverage alpha in LCD and update lcd blend gm.

src/gpu/effects/GrDistanceFieldGeoProc.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrDistanceFieldGeoProc.h"
 #include "GrInvariantOutput.h"
 #include "GrTexture.h"
@@ skipping 615 matching lines @@
             fsBuilder->codeAppend("}");
             fsBuilder->codeAppend("vec2 grad = vec2(dist_grad.x*Jdx.x + dist_grad.y*Jdy.x,");
             fsBuilder->codeAppend("                 dist_grad.x*Jdx.y + dist_grad.y*Jdy.y);");
 
             // this gives us a smooth step across approximately one fragment
             fsBuilder->codeAppend("afwidth = " SK_DistanceFieldAAFactor "*length(grad);");
         }
 
         fsBuilder->codeAppend(
                       "vec4 val = vec4(smoothstep(vec3(-afwidth), vec3(afwidth), distance), 1.0);");
+        // set alpha to be max of rgb coverage
+        fsBuilder->codeAppend("val.a = max(max(val.r, val.g), val.b);");
 
-        fsBuilder->codeAppendf("%s = vec4(val);", args.fOutputCoverage);
+        fsBuilder->codeAppendf("%s = val;", args.fOutputCoverage);
     }
 
     void setData(const GrGLProgramDataManager& pdman,
                  const GrPrimitiveProcessor& processor) override {
         SkASSERT(fDistanceAdjustUni.isValid());
 
         const GrDistanceFieldLCDTextGeoProc& dflcd = processor.cast<GrDistanceFieldLCDTextGeoProc>();
         GrDistanceFieldLCDTextGeoProc::DistanceAdjust wa = dflcd.getDistanceAdjust();
         if (wa != fDistanceAdjust) {
             pdman.set3f(fDistanceAdjustUni,
@@ skipping 100 matching lines @@
     uint32_t flags = kUseLCD_DistanceFieldEffectFlag;
     flags |= d->fRandom->nextBool() ? kUniformScale_DistanceFieldEffectMask : 0;
     flags |= d->fRandom->nextBool() ? kBGR_DistanceFieldEffectFlag : 0;
     return GrDistanceFieldLCDTextGeoProc::Create(GrRandomColor(d->fRandom),
                                                  GrTest::TestMatrix(d->fRandom),
                                                  d->fTextures[texIdx], params,
                                                  wa,
                                                  flags,
                                                  d->fRandom->nextBool());
 }