Implement SkImageFilter support in the compositor.

cc/layer_tree_host_common.cc

Index: cc/layer_tree_host_common.cc
diff --git a/cc/layer_tree_host_common.cc b/cc/layer_tree_host_common.cc
index bf5ec34892e6931729308e51ce207ea595c40801..30934d2fae7e05d29bf110df08d2813c9f2e551b 100644
--- a/cc/layer_tree_host_common.cc
+++ b/cc/layer_tree_host_common.cc
@@ -242,7 +242,7 @@ static bool subtreeShouldRenderToSeparateSurface(LayerType* layer, bool axisAlig
         return true;
 
     // If the layer uses a CSS filter.
-    if (!layer->filters().isEmpty() || !layer->backgroundFilters().isEmpty())
+    if (!layer->filters().isEmpty() || !layer->backgroundFilters().isEmpty() || layer->filter())
         return true;
 
     // If the layer flattens its subtree (i.e. the layer doesn't preserve-3d), but it is
@@ -576,7 +576,9 @@ static void calculateDrawTransformsInternal(LayerType* layer, LayerType* rootLay
             layer->replicaLayer()->maskLayer()->setVisibleContentRect(IntRect(IntPoint(), layer->contentBounds()));
         }
 
-        if (layer->filters().hasFilterThatMovesPixels())
+        // FIXME:  make this smarter for the SkImageFilter case (check for
+        //         pixel-moving filters)
+        if (layer->filters().hasFilterThatMovesPixels() || layer->filter())

[danakj, 2012/10/19 19:34:24]

There are a few other places that check for this: occlusion tracker, damage
tracker.

I see you got the opacity check in occlusion tracker, but not the moves pixels.

What does it mean for the filter outsets? In damage tracker and occlusion
tracker we add damage/remove occlusion based on the filter outsets.

Can an image filter move pixels? Or does it just change opacity/color values for
each pixel indepdently. If it can move color values from one pixel into another,
how far away? Is it completely arbitrary?

If arbitrary, then any damage in the layer needs to damage the whole layer in
damage tracker. Any non-occluded area on the layer needs to un-occlude the
entire layer in the occlusion tracker.

Maybe to help make common code we could add some templated static methods to
RenderSurfaceFilters to make queries about what filter effects a layer has, such
as hasFilterThatMovesPixels(), hasFilterThatAffectsOpacity(), filterOutsets(),
etc?

[Stephen White, 2012/10/19 21:34:50]

I think I got them all now.  Please let me know if I'm being appropriately
pessimistic.
An SkImageFilter can do anything it wants, really (although we only have a
limited set for SVG).  I think what we need to do is add movesPixels() and
affectsOpacity() virtuals to SkImageFilter, and do the right thing on all
subclasses over in Skia.
Could you check if I'm being pessimistic enough yet?  (Until the above functions
are implemented).
See above:  I think it needs to be on the SkImageFilter subclasses.

             nearestAncestorThatMovesPixels = renderSurface;
 
         // The render surface clipRect is expressed in the space where this surface draws, i.e. the same space as clipRectFromAncestor.