[Webkit-unassigned] [Bug 71385] Threaded compositor should delegate overflow div/iframe scroll events to WebKit

Wed Nov 23 05:03:18 PST 2011

https://bugs.webkit.org/show_bug.cgi?id=71385

--- Comment #7 from Sami Kyostila <skyostil at google.com>  2011-11-23 05:03:18 PST ---
(In reply to comment #6)
> (From update of attachment 116256 [details])
> I would think that in order to effectively be able to scroll on the thread, we'll first need to promote the scrolling element into a composited layer.  Then it will be a matter of marking an entire GraphicsLayer as scrollable.  The thread won't be able to repaint/scroll composited RLs that contain more than just the scrolling element.

I agree that for efficient scrolling we want to do exactly that. However, a concern I have is that are we really able to promote _every_ scrollable element to a GraphicsLayer? That could have significant memory and fillrate overhead. Also, I understood there is an issue with automatic promotion of overflow divs into layers due to the lack of a stacking context.

The patch I've attached enables the "slow path" (main thread) scrolling for elements that do not have their own layers. The next step is to make scrolling work for fully composited layers.

Do you think this approach makes sense, or is it safe to assume that all scrollable elements can be promoted to layers?

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