[webkit-reviews] review denied: [Bug 195378] Layer with no backing store should still hit-test over a scroller : [Attachment 365028] patch

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Mon Mar 18 11:13:53 PDT 2019

Simon Fraser (smfr) <simon.fraser at apple.com> has denied Antti Koivisto
<koivisto at iki.fi>'s request for review:
Bug 195378: Layer with no backing store should still hit-test over a scroller

Attachment 365028: patch


--- Comment #5 from Simon Fraser (smfr) <simon.fraser at apple.com> ---
Comment on attachment 365028
  --> https://bugs.webkit.org/attachment.cgi?id=365028

View in context: https://bugs.webkit.org/attachment.cgi?id=365028&action=review

r- to fix the pointer-events toggle issue (if it happens to work, please add a
test). Don't forget you can use immediateScrollElementAtContentPointToOffset

> Source/WebCore/rendering/RenderLayerBacking.cpp:768
> +	   updateEventRegion();

Here you're assuming that a layer configuration update will always happen when
something changes that affects where renderers are relative to their enclosing
compositing layer. This assumption relies on the fact that
RenderLayerBacking::setContentsNeedDisplay() calls
setNeedsCompositingConfigurationUpdate(), but if future optimizations allow us
to update layer configuration in fewer cases, that might break.

In fact, this might break now with something like:

  <div class="composited"><div id="child"></div>

and dynamic toggle of "pointer-events" style on child. That won't issue a
repaint (hopefully) and won't update event regions.

You should also add a testcase that just moves elements around and tests event
regions, so we can detect regressions caused by future compositing

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