Bug 139245

Summary: Programmatic scrolling and content changes are not always synchronized
Product: WebKit Reporter: Simon Fraser (smfr) <simon.fraser>
Component: Layout and RenderingAssignee: Simon Fraser (smfr) <simon.fraser>
Status: RESOLVED FIXED    
Severity: Normal CC: andersca, cmarcelo, commit-queue, jamesr, luiz, simon.fraser, thorton, tonikitoo, webkit-bug-importer
Priority: P2 Keywords: InRadar
Version: 528+ (Nightly build)   
Hardware: Unspecified   
OS: Unspecified   
Attachments:
Description Flags
Patch andersca: review+

Description Simon Fraser (smfr) 2014-12-03 17:20:56 PST 
Content that changes the scroll offset, and changes the style of an element at the same time should be able to make that element appear in a fixed position. However, for some reason WebKit is unable to always synchronize the two, and the element flickers.
Comment 1 Simon Fraser (smfr) 2014-12-03 17:21:14 PST 
rdar://problem/18833612
Comment 2 Simon Fraser (smfr) 2014-12-05 16:05:44 PST 
Even when programmatic scrolling, AsyncScrollingCoordinator::requestScrollPositionUpdate() sends the scroll off to the scrolling thread, which sometime later tells the UI thread that we scrolled in AsyncScrollingCoordinator::scheduleUpdateScrollPositionAfterAsyncScroll(), which (on a timer) hits AsyncScrollingCoordinator::updateScrollPositionAfterAsyncScroll().
Comment 3 Simon Fraser (smfr) 2014-12-05 17:04:50 PST 
Created attachment 242685 [details]
Patch
Comment 4 Simon Fraser (smfr) 2014-12-05 17:25:04 PST 
https://trac.webkit.org/r176899