After r260571, in the Nicosia scrolling mechanisms, scrolling changes applied onto the main-frame scrolling nodes through the RequestedScrollPosition state property change don't have any effect anymore. I assume this problem isn't exhibited on Mac/iOS. https://trac.webkit.org/changeset/260571/webkit This leaves the RequestedScrollPosition state changes to have no effect on the positioning of the layers, ergo scrolling via scrollbars or keyboard does not behave correctly. A call to applyLayerPositionsInternal() at the end of the ScrollingTree::commitTreeState() would for instance restore the correct behavior.
This is because of me juggling which when layer positions are applied. Layer positions should be getting applied at the end of the rendering updates; on macOS this happens in Page::finalizeRenderingUpdate().
(In reply to Simon Fraser (smfr) from comment #1) > This is because of me juggling which when layer positions are applied. > > Layer positions should be getting applied at the end of the rendering > updates; on macOS this happens in Page::finalizeRenderingUpdate(). That's what's needed, thanks for the tip.
Created attachment 399254 [details] Patch
Comment on attachment 399254 [details] Patch Thanks!
Comment on attachment 399254 [details] Patch Clearing flags on attachment: 399254 Committed r261616: <https://trac.webkit.org/changeset/261616>
All reviewed patches have been landed. Closing bug.
<rdar://problem/63183761>