Bug 52714

Summary:	Scrolling in compositing mode naively repaints non-composited parts of the page
Product:	WebKit	Reporter:	Adam Roben (:aroben) <aroben>
Component:	Layout and Rendering	Assignee:	Nobody <webkit-unassigned>
Status:	NEW ---
Severity:	Normal	CC:	cmarrin, simon.fraser, vangelis
Priority:	P2	Keywords:	InRadar, PlatformOnly
Version:	528+ (Nightly build)
Hardware:	PC
OS:	Windows XP

Description Adam Roben (:aroben) 2011-01-19 06:04:15 PST

The implementation of WebView::scrollBackingStore just calls m_backingLayer->setNeedsDisplayInRect(scrollViewRect), which will cause the non-composited parts of the page that intersect scrollViewRect to be repainted. This is a naive approach; it would be faster just to blit the contents into their new location and repaint only the newly-exposed contents.

Comment 1 Adam Roben (:aroben) 2011-01-19 06:07:48 PST

Perhaps we could take advantage of our layer-tiling code to improve this case.

Comment 2 Adam Roben (:aroben) 2011-01-19 06:08:15 PST

<rdar://problem/8884671>

Comment 3 Vangelis Kokkevis 2011-01-19 11:01:45 PST

(In reply to comment #1)
> Perhaps we could take advantage of our layer-tiling code to improve this case.

You might want to take a look at the chromium tiled root layer implementation in platform/graphics/chromium .  We recently switched over to a tiled root layer to improve scrolling performance.