Integrating SkSurface with SkDeferredCanvas

src/image/SkSurface_Raster.cpp

Index: src/image/SkSurface_Raster.cpp
===================================================================
--- src/image/SkSurface_Raster.cpp	(revision 8402)
+++ src/image/SkSurface_Raster.cpp	(working copy)
@@ -25,7 +25,7 @@
     virtual SkImage* onNewImageShapshot() SK_OVERRIDE;
     virtual void onDraw(SkCanvas*, SkScalar x, SkScalar y,
                         const SkPaint*) SK_OVERRIDE;
-    virtual void onCopyOnWrite(SkImage*, SkCanvas*) SK_OVERRIDE;
+    virtual void onCopyOnWrite(SkImage*, SkCanvas*, bool canDiscardContents) SK_OVERRIDE;
 
 private:
     SkBitmap    fBitmap;
@@ -124,15 +124,23 @@
     return SkNewImageFromBitmap(fBitmap, fWeOwnThePixels);
 }
 
-void SkSurface_Raster::onCopyOnWrite(SkImage* image, SkCanvas* canvas) {
+void SkSurface_Raster::onCopyOnWrite(SkImage* image, SkCanvas* canvas, bool canDiscardContents) {
     // are we sharing pixelrefs with the image?
     if (SkBitmapImageGetPixelRef(image) == fBitmap.pixelRef()) {
         SkASSERT(fWeOwnThePixels);
-        SkBitmap prev(fBitmap);
-        prev.deepCopyTo(&fBitmap, prev.config());
-        // Now fBitmap is a deep copy of itself (and therefore different from
-        // what is being used by the image. Next we update the canvas to use
-        // this as its backend, so we can't modify the image's pixels anymore.
+        if (canDiscardContents) {
+            SkBitmap newBitmap;
+            newBitmap.setConfig(fBitmap.getConfig(), fBitmap.width(), fBitmap.height(),
+                                fBitmap.rowBytes());
+            newBitmap.allocPixels();
+            fBitmap.swap(newBitmap);
+        } else {
+            SkBitmap prev(fBitmap);
+            prev.deepCopyTo(&fBitmap, prev.config());
+        }
+        // Now fBitmap is different from what is being used by the image.
+        // Next we update the canvas to use this as its backing store,
+        // so we can't modify the image's pixels anymore.
         canvas->getDevice()->replaceBitmapBackendForRasterSurface(fBitmap);
     }
 }