REGRESSION (r233268): contents of an animated element inside overflow:hidden disappear

• Component: Layout and Rendering
• Status: RESOLVED FIXED

[Antoine Quint]

Created attachment 347266 [details]
Test

The attached test case regressed with https://trac.webkit.org/changeset/233268 which was a fix for https://bugs.webkit.org/show_bug.cgi?id=186909. The issue goes away under several scenarios:

- use an <img> directly instead of a <picture>
- change .grid to not have explicit left and transform values and change slide-in to animate to translateX(100%)
- add an explicit 0% { transform: translateX(-100%) } keframe for the slide-in animation

[Radar WebKit Bug Importer]

<rdar://problem/43382687>

[Simon Fraser (smfr)]

Created attachment 354513 [details]
simpler test

[Simon Fraser (smfr)]

I think this happens when the un-animated state of the element has a transform. We are confused, in GraphicsLayerCA::computeVisibleAndCoverageRect(), about layerTransform and currentTransform, and seem to use different ones for layerBounds and coverageRect.

[Simon Fraser (smfr)]

Ah, the actual issue is that getOverlapBoundsIncludingChildrenAccountingForTransformAnimations() looks at keyframes to get the bounds, but in this example there is no 0% keyframe, so we fail to take the static translateX(-100%) into account.

[Simon Fraser (smfr)]

Created attachment 357283 [details]
Patch

[EWS Watchlist]

Comment on attachment 357283 [details]
Patch

Attachment 357283 [details] did not pass ios-sim-ews (ios-simulator-wk2):
Output: https://webkit-queues.webkit.org/results/10391430

New failing tests:
legacy-animation-engine/compositing/backing/backing-store-attachment-empty-keyframe.html
compositing/backing/backing-store-attachment-empty-keyframe.html

[EWS Watchlist]

Created attachment 357295 [details]
Archive of layout-test-results from ews121 for ios-simulator-wk2

The attached test failures were seen while running run-webkit-tests on the ios-sim-ews.
Bot: ews121  Port: ios-simulator-wk2  Platform: Mac OS X 10.13.6

[Simon Fraser (smfr)]

https://trac.webkit.org/changeset/239222/webkit