[Webkit-unassigned] [Bug 200668] Event region collection should take clipping into account

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=200668

Simon Fraser (smfr) <simon.fraser at apple.com> changed:

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--- Comment #3 from Simon Fraser (smfr) <simon.fraser at apple.com> ---
Comment on attachment 376161
  --> https://bugs.webkit.org/attachment.cgi?id=376161
patch

View in context: https://bugs.webkit.org/attachment.cgi?id=376161&action=review

> Source/WebCore/rendering/EventRegion.cpp:63
> +    m_clipStack.removeLast();

If we have mismatched push/pop, this will do shrink(size() - 1); which will underflow and create a huge vector and probably crash. I think we should be defensive here and check for m_clipStack not being empty.

This is especially true since we don't have save/restore, so you're doing manual push/pop.

> Source/WebCore/rendering/RenderBox.cpp:1821
> +    if (paintInfo.phase == PaintPhase::EventRegion)
> +        paintInfo.eventRegionContext->popClip();
> +
>      paintInfo.context().restore();

This is a manual pop, but the painting code is doing a save/restore. Maybe in future it would be better to implement save/restore for the event region context.

If I'm changing painting code in future, it's going to be really hard to know how to change the event region code.

Also, there may be other code paths that save/clip/restore that need to also do something with the event region.

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