Clarify when tweak alpha for coverage optimizaton can occur.

Also refer to it directly rather than using the term "modulate"

Change-Id: Ifa44a4d46e1be11b567943f58ead24e38f10d03b
Reviewed-on: https://skia-review.googlesource.com/8488
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/src/gpu/effects/GrSingleTextureEffect.h b/src/gpu/effects/GrSingleTextureEffect.h
index 894334b751..74b25c7053 100644
--- a/src/gpu/effects/GrSingleTextureEffect.h
+++ b/src/gpu/effects/GrSingleTextureEffect.h
@@ -54,15 +54,17 @@ protected:
                           sk_sp<GrColorSpaceXform>, const SkMatrix&, const GrSamplerParams&);
 
     /**
-     * Can be used as a helper to implement subclass onOptimizationFlags(). It assumes that
-     * the subclass output color will be a modulation of the input color with a value read from the
-     * texture.
+     * Can be used as a helper to decide which fragment processor OptimizationFlags should be set.
+     * This assumes that the subclass output color will be a modulation of the input color with a
+     * value read from the texture and that the texture contains premultiplied color or alpha values
+     * that are in range.
      */
     static OptimizationFlags ModulationFlags(GrPixelConfig config) {
         if (GrPixelConfigIsOpaque(config)) {
-            return kModulatesInput_OptimizationFlag | kPreservesOpaqueInput_OptimizationFlag;
+            return kCompatibleWithCoverageAsAlpha_OptimizationFlag |
+                   kPreservesOpaqueInput_OptimizationFlag;
         } else {
-            return kModulatesInput_OptimizationFlag;
+            return kCompatibleWithCoverageAsAlpha_OptimizationFlag;
         }
     }