[webkit-reviews] review denied: [Bug 92011] 50% fixed position coverage slow scroll heuristic is incorrect when invalidations aren't clipped : [Attachment 153871] Patch

[bugzilla-daemon at webkit.org]

Simon Fraser (smfr) <simon.fraser at apple.com> has denied Adrienne Walker
<enne at google.com>'s request for review:
Bug 92011: 50% fixed position coverage slow scroll heuristic is incorrect when
invalidations aren't clipped
https://bugs.webkit.org/show_bug.cgi?id=92011

Attachment 153871: Patch
https://bugs.webkit.org/attachment.cgi?id=153871&action=review

------- Additional Comments from Simon Fraser (smfr) <simon.fraser at apple.com>
I think our similar-but-different scrolling models are conflicting here.

On Mac Mountain Lion we use a tile cache behind the root's layer, so
contentsInCompositedLayer() is true. However, we don't have support for
compositing fixed elements, so we have to repaint fixed things on scrolling.
Once we put fixed things into composited layers, they'll be excluded from the
regionToUpdate. But the ! isCompositedContentLayer check doesn't appropriately
reflect the "content is painted into a layer which moves when you scroll and
doesn't need to repaint". That seems like a behavior that the
ScrollingCoordinator should export, like frameRepaintsOnScroll(FrameView*) or
something.