Fix ComposeOneFragmentProcessor coverage as alpha optimization.

It should only be advertised if the child also advertises it.

Change-Id: I698213c9562d710dff45f0622d50eacc41e29af5
Reviewed-on: https://skia-review.googlesource.com/8811
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>

1 files changed, 11 insertions, 5 deletions

diff --git a/src/gpu/effects/GrXfermodeFragmentProcessor.cpp b/src/gpu/effects/GrXfermodeFragmentProcessor.cpp
index 8488fec2ff..eb6f04b075 100644
--- a/src/gpu/effects/GrXfermodeFragmentProcessor.cpp
+++ b/src/gpu/effects/GrXfermodeFragmentProcessor.cpp
@@ -285,15 +285,21 @@ private:
                 break;
 
             // Produces opaque if both src and dst are opaque. These also will modulate the child's
-            // output by either the input color or alpha.
+            // output by either the input color or alpha. However, if the child is not compatible
+            // with the coverage as alpha then it may produce a color that is not valid premul.
             case SkBlendMode::kSrcIn:
             case SkBlendMode::kDstIn:
             case SkBlendMode::kModulate:
-                if (fp->preservesOpaqueInput()) {
-                    flags = kPreservesOpaqueInput_OptimizationFlag |
-                            kCompatibleWithCoverageAsAlpha_OptimizationFlag;
+                if (fp->compatibleWithCoverageAsAlpha()) {
+                    if (fp->preservesOpaqueInput()) {
+                        flags = kPreservesOpaqueInput_OptimizationFlag |
+                                kCompatibleWithCoverageAsAlpha_OptimizationFlag;
+                    } else {
+                        flags = kCompatibleWithCoverageAsAlpha_OptimizationFlag;
+                    }
                 } else {
-                    flags = kCompatibleWithCoverageAsAlpha_OptimizationFlag;
+                    flags = fp->preservesOpaqueInput() ? kPreservesOpaqueInput_OptimizationFlag
+                                                       : kNone_OptimizationFlags;
                 }
                 break;