Bug 118493

Summary: Deferring layer flushes can cause painting without layout being done
Product: WebKit Reporter: Tim Horton <thorton>
Component: Layout and RenderingAssignee: Tim Horton <thorton>
Status: RESOLVED FIXED    
Severity: Normal CC: andersca, koivisto, sam, simon.fraser
Priority: P2 Keywords: InRadar
Version: 528+ (Nightly build)   
Hardware: Unspecified   
OS: Unspecified   
Attachments:
Description Flags
preliminary patch
none
patch simon.fraser: review+

Tim Horton
Reported 2013-07-08 19:25:17 PDT
1. We depend on a run loop observer that fires just before CA does painting to ensure that layout is up-to-date. 2. TileController manually calls setNeedsDisplay on CALayers. 3. RenderLayerCompositor can (after r147797) defer #1 and cause it to not happen in the same run loop cycle as #2. 4. This means that we can end up painting without layout being up-to-date, which can cause horrible, horrible graphical issues. We need to not defer (#3) if TileController has setNeedsDisplay'd any layers manually (or if we've added any new dirty layers). <rdar://problem/14286329>
Attachments
preliminary patch (5.45 KB, patch)
2013-07-10 04:03 PDT, Tim Horton 		no flags
DetailsFormatted DiffDiff
patch (7.88 KB, patch)
2013-07-10 13:01 PDT, Tim Horton 		simon.fraser: review+
DetailsFormatted DiffDiff
Show Obsolete (1) View All Add attachment proposed patch, testcase, etc.
Tim Horton
Comment 1 2013-07-08 19:27:11 PDT
One of the best repro cases of actual real world badness caused by this is http://www.mercurynews.com, which frequently shows garbage (or black) upon loading.
Tim Horton
Comment 2 2013-07-10 03:53:47 PDT
#2 is actually "TileController can parent layers which had setNeedsDisplay called on them long ago, but were unparented"
Tim Horton
Comment 3 2013-07-10 04:03:27 PDT
Created attachment 206378 [details] preliminary patch
Tim Horton
Comment 4 2013-07-10 13:01:40 PDT
Created attachment 206409 [details] patch
Antti Koivisto
Comment 5 2013-07-10 13:36:02 PDT
Comment on attachment 206409 [details] patch For the benefit of future debuggers, it might be good to add a comment above platformCALayerDidCreateTiles call as it is not that obvious that it initiates an immediate layer flush.
Tim Horton
Comment 6 2013-07-10 13:38:52 PDT
(In reply to comment #5) > (From update of attachment 206409 [details]) > For the benefit of future debuggers, it might be good to add a comment above platformCALayerDidCreateTiles call as it is not that obvious that it initiates an immediate layer flush. True. I'll do that.
Tim Horton
Comment 7 2013-07-10 14:19:02 PDT
http://trac.webkit.org/changeset/152548
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