775912 - Smooth scrolling isn't initially smooth because of multiple repaints

Status: RESOLVED WORKSFORME

(Core :: Layout, defect)

Description

[Marco Castelluccio [:marco]]

Smooth scrolling isn't smooth when the animation starts, but just after you've scrolled a bit.
This is simply reproducible on Facebook.

Comment 1

[Jared Wein [:jaws] (please needinfo? me)]

Pretty sure that at least this bug is a duplicate of bug 728153. Please reopen if you disagree.

Comment 2

[Marco Castelluccio [:marco]]

That bug is about an unnoticeable lag, instead this one is very visible.
Note that I can't reproduce on Linux.

Comment 3

[Marco Castelluccio [:marco]]

Jared, this problem is noticeable if you enable nglayout.debug.paint_flashing.
There's a pause in the animation if you scroll from the top of the Facebook home, because the entire content of the page is repainted. Instead, if you start to scroll from somewhere else, just some content is repainted.

Let me know if I wasn't enough clear.

Comment 4

[Marco Castelluccio [:marco]]

Actually, when you scroll down a Facebook page and a loading of new content happens, there are some pauses due to multiple repaints of the content (even of the unchanged content).
I guess on slower computers this is a nightmare.

Is this something that could be fixed by DLBI?

Comment 5

[Marco Castelluccio [:marco]]

Tried with the try build in bug 539356 and indeed the problem is fixed with DLBI.

Comment 6

[Marco Castelluccio [:marco]]

With the try build the problem was fixed, but in Firefox 18 I still see multiple repaints of the entire content while scrolling.

Comment 7

[(dormant account)]

There isn't much we can do at the moment about separating scrolling a pageloading. Will reconsider once we can do async scrolling with OMTC.

Comment 8

[Florian Bender]

Would Bug 645563 help here, too?