Support color animated properties

[nical]

Animating things like background colors isn't uncommon, should be fairly straight forward to do in webrender without rebuilding the scene and is typically expensive in Gecko without webrender because the latter relies on invalidation->repaint->double-buffering->texture-upload.

While not high priority, it would make for a fun feature to show off webrender's architecture.

[pcwalton]

Bugzilla bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1371101

[glennw]

Would this resolve all the CPU issues in the MotionMark Multiply test when implemented? That test basically has a heap of border corners with animated color and rotating transform. Once this is implemented, we could probably run that benchmark without rebuilding the display list at all?

Steps to implement this are:

• Extend PropertyBinding to support ColorF.
• Change the color field in a rectangle to a PropertyBinding.
• Resolve that property binding during frame build.

Added an easy tag, since this should be quite straightforward.

[pcwalton]

The hard part here is implementing the Gecko style system bit, as I understand things. In particular, my understanding is that we need a new nsChangeHint for color changes.

[ncarrillo]

I think this may be a bit more involved, I gave this a go and couldn't get changes included in GenerateFrame to produce an updated result.

diff --git a/webrender/src/frame.rs b/webrender/src/frame.rs
index 9f0921ff..753315c1 100644
--- a/webrender/src/frame.rs
+++ b/webrender/src/frame.rs
@@ -451,13 +451,13 @@ impl<'a> FlattenContext<'a> {
             SpecificDisplayItem::Rectangle(ref info) => {
                 if !self.try_to_add_rectangle_splitting_on_clip(
                     &prim_info,
-                    RectangleContent::Fill(info.color),
+                    RectangleContent::Fill(self.scene.properties.resolve_color(&info.color)),
                     &clip_and_scroll,
                 ) {
                     self.builder.add_solid_rectangle(
                         clip_and_scroll,
                         &prim_info,
-                        RectangleContent::Fill(info.color),
+                        RectangleContent::Fill(self.scene.properties.resolve_color(&info.color)),
                         None,
                     );
                 }

[glennw]

Ah, I should have been more specific in my description - that code there only executes once for a new display list. The resolve would actually need to be done later (probably in prepare_prim_for_render would be ideal).

[ncarrillo]

I'm working on this on the WR side, and I have it working for simple Rects. I was able to get it working in prepare_prim_for_render by looking up the cpu_rectangle entry, modifying the RectangleContent and invalidating the metadata.gpu_location

I've run into some difficulty with how places like the border/box shadow code expect a resolved value, my current thought is to expand PropertyBinding::Binding to include the latest resolved value.

I've moved over the definition of FilterOp::Opacity to store the initial value of the opacity there as well.

[glennw]

I think that sounds like a good approach.