Allow the alpha folding optimization if the single draw's paint has a shader

src/core/SkRecordOpts.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 "SkRecordOpts.h"
 
 #include "SkRecordPattern.h"
@@ skipping 94 matching lines @@
         SkPaint* drawPaint = pattern->second<SkPaint>();
         if (drawPaint == NULL) {
             // We can just give the draw the SaveLayer's paint.
             // TODO(mtklein): figure out how to do this clearly
             return false;
         }
 
         const uint32_t layerColor = layerPaint->getColor();
         const uint32_t  drawColor =  drawPaint->getColor();
         if (!IsOnlyAlpha(layerColor)  || !IsOpaque(drawColor) ||
-            HasAnyEffect(*layerPaint) || HasAnyEffect(*drawPaint)) {
+            HasAnyEffect(*layerPaint) || CantFoldAlpha(*drawPaint)) {
             // Too fancy for us.  Actually, as long as layerColor is just an alpha
             // we can blend it into drawColor's alpha; drawColor doesn't strictly have to be opaque.
             return false;
         }
 
         drawPaint->setColor(SkColorSetA(drawColor, SkColorGetA(layerColor)));
         return KillSaveLayerAndRestore(record, begin);
     }
 
     static bool KillSaveLayerAndRestore(SkRecord* record, unsigned saveLayerIndex) {
         record->replace<NoOp>(saveLayerIndex);    // SaveLayer
         record->replace<NoOp>(saveLayerIndex+2);  // Restore
         return true;
     }
 
     static bool HasAnyEffect(const SkPaint& paint) {
         return paint.getPathEffect()  ||
                paint.getShader()      ||
                paint.getXfermode()    ||
                paint.getMaskFilter()  ||
                paint.getColorFilter() ||
                paint.getRasterizer()  ||
                paint.getLooper()      ||
                paint.getImageFilter();
     }
 
+    // The alpha folding can proceed if the single draw's paint has a shader,
+    // path effect, mask filter and/or rasterizer.
+    // TODO: most likely the looper and only some xfer modes are the hard
+    // constraints
+    static bool CantFoldAlpha(const SkPaint& paint) {
+        return paint.getXfermode()    ||
+               paint.getColorFilter() ||
+               paint.getLooper()      ||
+               paint.getImageFilter();
+    }
+
     static bool IsOpaque(SkColor color) {
         return SkColorGetA(color) == SK_AlphaOPAQUE;
     }
     static bool IsOnlyAlpha(SkColor color) {
         return SK_ColorTRANSPARENT == SkColorSetA(color, SK_AlphaTRANSPARENT);
     }
 };
 void SkRecordNoopSaveLayerDrawRestores(SkRecord* record) {
     SaveLayerDrawRestoreNooper pass;
     apply(&pass, record);
 }