[webkit-changes] [WebKit/WebKit] b56add: Overflow:hidden fails on a transformed element ins...

[Simon Fraser]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: b56addc7fbfd92f4d7f2ac43380703d589829fdb
      https://github.com/WebKit/WebKit/commit/b56addc7fbfd92f4d7f2ac43380703d589829fdb
  Author: Simon Fraser <simon.fraser at apple.com>
  Date:   2024-10-08 (Tue, 08 Oct 2024)

  Changed paths:
    A LayoutTests/compositing/scrolling/transformed-clipping-inside-scroller-expected.html
    A LayoutTests/compositing/scrolling/transformed-clipping-inside-scroller.html
    M LayoutTests/compositing/transforms/3d-transformed-fixed.html
    M Source/WebCore/rendering/RenderLayer.cpp
    M Source/WebCore/rendering/RenderLayer.h

  Log Message:
  -----------
  Overflow:hidden fails on a transformed element inside overflow scroll (affects motionpictures.org, www.bogleheads.org)
https://bugs.webkit.org/show_bug.cgi?id=281073
rdar://66751438

Reviewed by Alan Baradlay.

When `paintLayerByApplyingTransform()` paints a layer with a transform, that layer becomes a painting
root, which means that clip rects are computed relative to it. However, `RenderLayer::calculateRects()`
has logic that is conditional on a layer being the painting root and `clipRectsContext.respectOverflowClip()`
being unset, resulting in the clip being ignored. `clipRectsContext.respectOverflowClip()` is false for all descendants
of content being painted into an overflow scroller (see `clipRectOptionsForPaintingOverflowContents`).

So a transformed and clipped element inside an overflow scroller would fail to apply the clipping.

Fix this in `paintLayerByApplyingTransform`, since that's the only place we reset the painting root,
by clearing the `PaintLayerFlag::PaintingOverflowContents` painting flag.

Also rename `clipRectOptionsForPaintingOverflowControls`, since it's about painting content inside
overflow, not about overflow controls.

* LayoutTests/compositing/scrolling/transformed-clipping-inside-scroller-expected.html: Added.
* LayoutTests/compositing/scrolling/transformed-clipping-inside-scroller.html: Added.
* LayoutTests/compositing/transforms/3d-transformed-fixed.html: Just add some pixel tolerance so it passes on my machine.
* Source/WebCore/rendering/RenderLayer.cpp:
(WebCore::RenderLayer::paintLayerWithEffects):
(WebCore::RenderLayer::paintLayerContents):
(WebCore::RenderLayer::paintLayerByApplyingTransform):
(WebCore::RenderLayer::paintTransformedLayerIntoFragments):
* Source/WebCore/rendering/RenderLayer.h:

Canonical link: https://commits.webkit.org/284872@main



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