Update invariant output computation for various texture effects.

src/effects/SkAlphaThresholdFilter.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 "SkAlphaThresholdFilter.h"
 #include "SkBitmap.h"
 #include "SkReadBuffer.h"
@@ skipping 211 matching lines @@
     return GrTBackendFragmentProcessorFactory<AlphaThresholdEffect>::getInstance();
 }
 
 bool AlphaThresholdEffect::onIsEqual(const GrFragmentProcessor& sBase) const {
     const AlphaThresholdEffect& s = sBase.cast<AlphaThresholdEffect>();
     return (this->fInnerThreshold == s.fInnerThreshold &&
             this->fOuterThreshold == s.fOuterThreshold);
 }
 
 void AlphaThresholdEffect::onComputeInvariantOutput(GrInvariantOutput* inout) const {
-    if (GrPixelConfigIsOpaque(this->texture(0)->config()) && fOuterThreshold >= 1.f) {
+    if (GrPixelConfigIsAlphaOnly(this->texture(0)->config())) {
+        inout->mulByUnknownAlpha();
+    } else if (GrPixelConfigIsOpaque(this->texture(0)->config()) && fOuterThreshold >= 1.f) {
         inout->mulByUnknownOpaqueColor();
     } else {
         inout->mulByUnknownColor();
     }
 }
 
 #endif
 
 #ifdef SK_SUPPORT_LEGACY_DEEPFLATTENING
 SkAlphaThresholdFilterImpl::SkAlphaThresholdFilterImpl(SkReadBuffer& buffer)
@@ skipping 135 matching lines @@
                                                   (U8CPU)(SkColorGetG(source) * scale),
                                                   (U8CPU)(SkColorGetB(source) * scale));
                 }
             }
             dptr[y * dst->width() + x] = output_color;
         }
     }
 
     return true;
 }