Bug 544399. Use nsLayoutUtils::SurfaceFromElement when comparing canvases. r=vlad

--HG--
extra : rebase_source : 93f22c10faa3bad9dbff48cd823f38d4a6ffc22a

dom/base/nsDOMWindowUtils.cpp

@@ -63,6 +63,7 @@
 #include "nsICanvasElement.h"
 #include "gfxContext.h"
 #include "gfxImageSurface.h"
+#include "nsLayoutUtils.h"
 
 #if defined(MOZ_X11) && defined(MOZ_WIDGET_GTK2)
 #include <gdk/gdk.h>
@@ -621,33 +622,10 @@ nsDOMWindowUtils::ElementFromPoint(PRInt32 aX, PRInt32 aY,
 static already_AddRefed<gfxImageSurface>
 CanvasToImageSurface(nsIDOMHTMLCanvasElement *canvas)
 {
-  PRUint32 w, h;
-  nsresult rv;
-
-  nsCOMPtr<nsICanvasElement> elt = do_QueryInterface(canvas);
-  rv = elt->GetSize(&w, &h);
-  if (NS_FAILED(rv))
-    return nsnull;
-
-  nsRefPtr<gfxImageSurface> img = new gfxImageSurface(gfxIntSize(w, h), gfxASurface::ImageFormatARGB32);
-  if (img == nsnull)
-    return nsnull;
-
-  nsRefPtr<gfxContext> ctx = new gfxContext(img);
-  if (ctx == nsnull)
-    return nsnull;
-
-  ctx->SetOperator(gfxContext::OPERATOR_CLEAR);
-  ctx->Paint();
-
-  ctx->SetOperator(gfxContext::OPERATOR_OVER);
-  rv = elt->RenderContexts(ctx, gfxPattern::FILTER_NEAREST);
-  if (NS_FAILED(rv))
-    return nsnull;
-
-  ctx = nsnull;
-
-  return img.forget();
+  nsLayoutUtils::SurfaceFromElementResult result =
+    nsLayoutUtils::SurfaceFromElement(canvas,
+                                      nsLayoutUtils::SFE_WANT_IMAGE_SURFACE);
+  return static_cast<gfxImageSurface*>(result.mSurface.forget().get());
 }
 
 NS_IMETHODIMP