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

[bugzilla-daemon at webkit.org]

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

--- Comment #14 from Simon Fraser (smfr) <simon.fraser at apple.com> ---
Some more detail:

The geometry of fixed layers is based on the geometry of layers in the z-order ancestor chain (because the layer tree is unavoidably in z-order, because that's the only way to have CA do the right back-to-front ordering. That means that a fixed layer can be deeply nested in the z-order tree; even though its containing block is trivially the RenderView, we must compute the position for that fixed layer relative to its parent in z-order, which can be some arbitrary layer, even inside of overflow:scroll.

That, in turn, means that layout information is baked into FixedPositionViewportConstraints::m_layerPositionAtLastLayout, and we need pass m_viewportRectAtLastLayout in order to compute deltas in the scrolling tree.

This means that it's impossible to unbake scroll positions out of inputs to the scrolling tree in anything other than the most trivial cases.

-- 
You are receiving this mail because:
You are the assignee for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.webkit.org/pipermail/webkit-unassigned/attachments/20190307/541adda4/attachment-0001.html>