Bug 113238 – Non-paintsContent fixed position layer should not cause main-thread scrolling

• Component: Layout and Rendering
• Status: RESOLVED FIXED

[Xianzhu Wang]

Should record the reason of not-compositing non-paintsContent fixed position layer so that ScrollingCoordinator won't treat the layer as a fast-scrolling blocker.

[Xianzhu Wang]

Created attachment 194946 [details]
Patch

[Sami Kyöstilä]

Thanks Xianzhu, I think this looks great.

[Xianzhu Wang]

Simon, could you please review the patch? Thanks.

[James Robinson]

Comment on attachment 194946 [details]
Patch

R=me, this looks great.  See if you can get Simon to take a look as well before landing.

[Simon Fraser (smfr)]

I think bug 110430 covers the same issue.

[Xianzhu Wang]

Comment on attachment 194946 [details]
Patch

Assuming no objection from Simon :)

[Simon Fraser (smfr)]

Comment on attachment 194946 [details]
Patch

Where is NotCompositedForNoVisibleContent actually consulted? I would expect to see a test for it in FrameView::scrollContentsFastPath(), but do not.

[WebKit Review Bot]

Comment on attachment 194946 [details]
Patch

Clearing flags on attachment: 194946

Committed r146940: <http://trac.webkit.org/changeset/146940>

[WebKit Review Bot]

All reviewed patches have been landed.  Closing bug.

[Simon Fraser (smfr)]

Please respond to my comment.

[Xianzhu Wang]

(In reply to comment #7)
> (From update of attachment 194946 [details])
> Where is NotCompositedForNoVisibleContent actually consulted? I would expect to see a test for it in FrameView::scrollContentsFastPath(), but do not.

In ScrollingCoordinator::hasVisibleSlowRepaintViewportConstrainedObjects(), there is an existing test that any viewport constrained object not composited with explicit reasons (layer->viewportConstrainedNotCompositedReason() != RenderLayer::NoNotCompositedReason) won't cause main-thread scrolling.

Seems that we need the same test in FrameView::scrollContentsFastPath().

[Xianzhu Wang]

(In reply to comment #11)
> (In reply to comment #7)
> > (From update of attachment 194946 [details] [details])
> > Where is NotCompositedForNoVisibleContent actually consulted? I would expect to see a test for it in FrameView::scrollContentsFastPath(), but do not.
> 
> In ScrollingCoordinator::hasVisibleSlowRepaintViewportConstrainedObjects(), there is an existing test that any viewport constrained object not composited with explicit reasons (layer->viewportConstrainedNotCompositedReason() != RenderLayer::NoNotCompositedReason) won't cause main-thread scrolling.
> 
> Seems that we need the same test in FrameView::scrollContentsFastPath().

This seems what bug 110430 covers. This bug covers the main-thread scrolling issue caused by no-content fixed element. I should have used "main-thread scrolling" instead of ambiguous "slow-scrolling"/"fast-scrolling". Will work on bug 110430 for the remaining issue in FrameView::scrollContentsFastPath().