Programmatic scrolling and content changes are not always synchronized
https://bugs.webkit.org/show_bug.cgi?id=139245
rdar://problem/18833612
Reviewed by Anders Carlsson.
Manual test that tries to sync layout with programmatic scrolling.
* ManualTests/programmatic-scroll-flicker.html: Added.
Source/WebCore:
For programmatic scrolls, AsyncScrollingCoordinator::requestScrollPositionUpdate()
calls updateScrollPositionAfterAsyncScroll(), then dispatches the requested
scroll position to the scrolling thread.
Once the scrolling thread commits, it calls back to the main thread via
scheduleUpdateScrollPositionAfterAsyncScroll(), which schedules a second
call to updateScrollPositionAfterAsyncScroll() on a timer. That's a problem,
because some other scroll may have happened in the meantime; when the timer
fires, it can sometimes restore a stale scroll position.
Fix by bailing early from scheduleUpdateScrollPositionAfterAsyncScroll()
for programmatic scrolls, since we know that requestScrollPositionUpdate()
already did the updateScrollPositionAfterAsyncScroll().
Test:
ManualTests/programmatic-scroll-flicker.html
* page/FrameView.cpp:
(WebCore::FrameView::reset): nullptr.
(WebCore::FrameView::setScrollPosition): Ditto.
(WebCore::FrameView::setWasScrolledByUser): Ditto.
* page/scrolling/AsyncScrollingCoordinator.cpp:
(WebCore::AsyncScrollingCoordinator::requestScrollPositionUpdate): Use a local variable for
isProgrammaticScroll just to make sure we use the same value for the duration of this function.
(WebCore::AsyncScrollingCoordinator::scheduleUpdateScrollPositionAfterAsyncScroll): Do nothing
if this is a programmatic scroll.
git-svn-id: http://svn.webkit.org/repository/webkit/trunk@176899 268f45cc-cd09-0410-ab3c-d52691b4dbfc
5 files changed
