Overflow scrolling layers need to be self-painting

[Simon Fraser (smfr)]

Overflow scrolling layers need to be self-painting

[Simon Fraser (smfr)]

Created attachment 356092 [details]
Patch

[Radar WebKit Bug Importer]

<rdar://problem/46359460>

[Simon Fraser (smfr)]

Depends on a previous patch.

[Simon Fraser (smfr)]

https://trac.webkit.org/changeset/238725/webkit

[Ali Juma]

(In reply to Simon Fraser (smfr) from comment #0)
> Overflow scrolling layers need to be self-painting

Won't this change paint order for those overflow scrollers that didn't get self-painting layers before? (Since instead of being painted when other in-flow elements are painted they'll now get painted with other self-painting layers.)

[Truitt Savell]

The new test added in https://trac.webkit.org/changeset/238725/webkit

compositing/scrolling/overflow-scrolling-layers-are-self-painting.html is failing

Diff:
--- /Volumes/Data/slave/ios-simulator-12-release-tests-wk2/build/layout-test-results/compositing/scrolling/overflow-scrolling-layers-are-self-painting-expected.txt
+++ /Volumes/Data/slave/ios-simulator-12-release-tests-wk2/build/layout-test-results/compositing/scrolling/overflow-scrolling-layers-are-self-painting-actual.txt
@@ -14,11 +14,11 @@
             (GraphicsLayer
               (offsetFromRenderer width=-1 height=-1)
               (position 1.00 1.00)
-              (bounds 285.00 285.00)
+              (bounds 300.00 300.00)
               (children 1
                 (GraphicsLayer
                   (offsetFromRenderer width=1 height=1)
-                  (bounds 285.00 2000.00)
+                  (bounds 300.00 2000.00)
                 )
               )
             )

History:
https://webkit-test-results.webkit.org/dashboards/flakiness_dashboard.html#showAllRuns=true&tests=compositing%2Fscrolling%2Foverflow-scrolling-layers-are-self-painting.html

[Simon Fraser (smfr)]

Test needs iOS results (though I could have sworn I ran the test for iOS before landing).

(In reply to Ali Juma from comment #5)
> (In reply to Simon Fraser (smfr) from comment #0)
> > Overflow scrolling layers need to be self-painting
> 
> Won't this change paint order for those overflow scrollers that didn't get
> self-painting layers before? (Since instead of being painted when other
> in-flow elements are painted they'll now get painted with other
> self-painting layers.)

Yes, but I'm not sure we have a choice. We do the same for things like video and canvas, and it hasn't been a problem.

[Truitt Savell]

added iOS specific expectations in https://trac.webkit.org/changeset/238765/webkit