785588 - Janky scrolling with parallax background effect

Status: RESOLVED FIXED

(Core :: Graphics, defect)

Description

[Jesse Ruderman]

Scrolling http://chrsl.net/gospel/ doesn't feel smooth at all.  The background almost seems to lag behind the text.

[Nightly 17.0a1 (2012-08-22), pixel-scrolling with two fingers on trackpad]

Comment 1

[Robert O'Callahan (:roc) (email my personal email if necessary)]

stellar.js runs a requestAnimationFrame loop which polls the current scroll position and updates background positions accordingly. I think the problem is AsyncScroll adds itself as a Flush_Display refresh observer, meaning that requestAnimationFrame callbacks run before the scroll event. So the sequence of events is:
1) user triggers scroll
2) refresh driver runs:
2a) stellar.js's requestAnimationFrame callback runs, sees nothing has changed
2b) AsyncScroll callback runs and updates scroll position
2c) repaint the window due to scroll
3) refresh driver runs again
3a) stellar.js's requestAnimationFrame callback runs, updates background for new scroll position
3b) repaint the window again for the new background

Comment 2

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: fix

Comment 3

[Robert O'Callahan (:roc) (email my personal email if necessary)]

https://hg.mozilla.org/integration/mozilla-inbound/rev/0b354d6a9c90

After this has landed for a bit, I think we should lift it up to Aurora, but not Beta. This is not a regression and the way stellar.js polls scroll positions with requestAnimationFrame (and not, say, an onscroll handler) is a bit strange.

Comment 4

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/0b354d6a9c90

Comment 5

[Jesse Ruderman]

It still doesn't feel smooth to me.  I filed bug 791424 rather than reopening this.