Expand filter 0 to handle transparent drawBitmapRect paints

tools/filtermain.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkDebugCanvas.h"
 #include "SkDevice.h"
 #include "SkGraphics.h"
@@ skipping 43 matching lines @@
         return false;
     }
 
     SaveLayer* saveLayer = (SaveLayer*) canvas->getDrawCommandAt(curCommand);
     DrawBitmapRect* dbmr = (DrawBitmapRect*) canvas->getDrawCommandAt(curCommand+1);
 
     const SkPaint* saveLayerPaint = saveLayer->paint();
     SkPaint* dbmrPaint = dbmr->paint();
 
     // For this optimization we only fold the saveLayer and drawBitmapRect
-    // together if the saveLayer's draw is simple (i.e., no fancy effects) and
-    // and the only difference in the colors is that the saveLayer's can have
-    // an alpha while the drawBitmapRect's is opaque.
-    // TODO: it should be possible to fold them together even if they both
-    // have different non-255 alphas but this is low priority since we have
-    // never seen that case
+    // together if the saveLayer's draw is simple (i.e., no fancy effects)
+    // and the only difference in the colors is their alpha value
+    SkColor layerColor = saveLayerPaint->getColor() | 0xFF000000; // force opaque
+    SkColor dbmrColor = dbmrPaint->getColor() | 0xFF000000;       // force opaque
+
     // If either operation lacks a paint then the collapse is trivial
-    SkColor layerColor = saveLayerPaint->getColor() | 0xFF000000; // force opaque
-
     return NULL == saveLayerPaint ||
            NULL == dbmrPaint ||
-           (is_simple(*saveLayerPaint) && dbmrPaint->getColor() == layerColor);
+           (is_simple(*saveLayerPaint) && dbmrColor == layerColor);
 }
 
 // Fold the saveLayer's alpha into the drawBitmapRect and remove the saveLayer
 // and restore
 static void apply_0(SkDebugCanvas* canvas, int curCommand) {
     SaveLayer* saveLayer = (SaveLayer*) canvas->getDrawCommandAt(curCommand);
     const SkPaint* saveLayerPaint = saveLayer->paint();
 
     // if (NULL == saveLayerPaint) the dbmr's paint doesn't need to be changed
     if (NULL != saveLayerPaint) { 
         DrawBitmapRect* dbmr = (DrawBitmapRect*) canvas->getDrawCommandAt(curCommand+1);
         SkPaint* dbmrPaint = dbmr->paint();
 
         if (NULL == dbmrPaint) {
             // if the DBMR doesn't have a paint just use the saveLayer's
             dbmr->setPaint(*saveLayerPaint);
         } else if (NULL != saveLayerPaint) {
-            SkColor newColor = SkColorSetA(dbmrPaint->getColor(),
-                                           SkColorGetA(saveLayerPaint->getColor()));
+            // Both paints are present so their alphas need to be combined
+            SkColor color = saveLayerPaint->getColor();
+            int a0 = SkColorGetA(color);
+
+            color = dbmrPaint->getColor();
+            int a1 = SkColorGetA(color);
+
+            int newA = (a0 * a1) / 255;

[bsalomon, 2013/04/02 14:53:27]

It seems like there's probably some alpha mul macro that should be used here.

[bsalomon, 2013/04/02 14:55:53]

SkMulDiv255Round?

[robertphillips, 2013/04/02 15:30:22]

Done.

+            SkASSERT(newA <= 0xFF);
+
+            SkColor newColor = SkColorSetA(color, newA);
             dbmrPaint->setColor(newColor);
         }
     }
 
     canvas->deleteDrawCommandAt(curCommand+2);  // restore
     canvas->deleteDrawCommandAt(curCommand);    // saveLayer
 }
 
 // Check for:
 //    SAVE_LAYER
@@ skipping 684 matching lines @@
 
     SkGraphics::Term();
     return 0;
 }
 
 #if !defined SK_BUILD_FOR_IOS
 int main(int argc, char * const argv[]) {
     return tool_main(argc, (char**) argv);
 }
 #endif