Bug 210506

Summary: [Async overflow scroll] Backgrounds missing on gmail sometimes
Product: WebKit Reporter: Simon Fraser (smfr) <simon.fraser>
Component: CompositingAssignee: Simon Fraser (smfr) <simon.fraser>
Status: RESOLVED FIXED    
Severity: Normal CC: esprehn+autocc, ews-watchlist, fred.wang, glenn, kondapallykalyan, pdr, simon.fraser, webkit-bug-importer, zalan
Priority: P2 Keywords: InRadar
Version: Safari Technology Preview   
Hardware: Unspecified   
OS: Unspecified   
Attachments:
Description Flags
Reduction
none
Patch
none
Patch zalan: review+

Simon Fraser (smfr)
Reported 2020-04-14 11:26:57 PDT
Created attachment 396443 [details] Reduction Element backgrounds fail to paint sometimes when scrolling in gmail with async overflow scrolling enabled.
Attachments
Reduction (1.11 KB, text/html)
2020-04-14 11:26 PDT, Simon Fraser (smfr) 		no flags
Details
Patch (9.45 KB, patch)
2020-04-14 16:48 PDT, Simon Fraser (smfr) 		no flags
DetailsFormatted DiffDiff
Patch (15.57 KB, patch)
2020-04-14 20:48 PDT, Simon Fraser (smfr) 		zalan: review+
DetailsFormatted DiffDiff
Show Obsolete (1) View All Add attachment proposed patch, testcase, etc.
Simon Fraser (smfr)
Comment 1 2020-04-14 11:27:13 PDT
rdar://problem/60523869
Simon Fraser (smfr)
Comment 2 2020-04-14 11:58:45 PDT
I think this is about painting with stale clip rects (which are probably computed using some stale main-thread scrolling offset).
Simon Fraser (smfr)
Comment 3 2020-04-14 14:04:45 PDT
We paint out-of-view tiles but RenderBlock::paint() short-circuits because they are clipped out (note the iOS #ifdef), then we later scroll those tiles back into view and they are missing content.
Simon Fraser (smfr)
Comment 4 2020-04-14 15:42:40 PDT
RenderBox::overflowRectForPaintRejection() is supposed to handle this, but m_overflow is null for some reason.
Simon Fraser (smfr)
Comment 5 2020-04-14 16:48:55 PDT
Created attachment 396478 [details] Patch
Simon Fraser (smfr)
Comment 6 2020-04-14 20:48:37 PDT
Created attachment 396494 [details] Patch
Simon Fraser (smfr)
Comment 7 2020-04-14 23:35:28 PDT
https://trac.webkit.org/changeset/260118/webkit
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