[Webkit-unassigned] [Bug 194289] Glitch-free async scrolling

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=194289

--- Comment #15 from Simon Fraser (smfr) <simon.fraser at apple.com> ---
With fixed, there's one thing you could do: tell the scrolling tree the viewport-relative offsets, then, on the scrolling thread/UI process side, do two -[layer convertPoint:toLayer:] to the root, and to the parent layer, and then set the fixed layer positions as the difference. However, that means you're using the CALayer tree as a source of data, so you risk racing with layer flushing (on macOS).

Also, that wouldn't work for sticky, where part of the constraints are containing block bounds, which aren't represented in the layer or scrolling trees at present. It would also not work for my up-coming positioned layers, whose containing blocks aren't represented in either tree either.

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