1325366 - blank region painted while dragging scroll thumb on irccloud

Status: RESOLVED WORKSFORME

(Core :: Panning and Zooming, defect, P3)

Description

[Ben Kelly [:bkelly, not reviewing]]

Attachment: Screenshot 2016-12-22 09.11.58.png

This morning in 53.0a1 (2016-12-21) (64-bit) on windows 10 I did the following:

1) Unlock computer and notice I have some mentions in irccloud in #developers
2) Scroll back to find the mentions from the previous night.
3) Grab scroll thumb to pull back to bottom
4) When I pull to the bottom the chat window content goes blank (see attached screenshot)

Its possible that in (4) I pulled to the bottom, but also moved my mouse cursor a bit to the right out of the text box.  Not sure if that does something to the scroll position.

I've never seen this behavior before, so I'm guessing its somehow related to the new APZC on scroll dragging.  Kats, can you reproduce this?  You might need to let a largish amount of backscroll develop in #developers before trying.

Comment 1

[Ben Kelly [:bkelly, not reviewing]]

Note, it doesn't happen every time.  Sometimes I have to drag the scroll thumb up and down for a while.  It seems like maybe its related to irccloud modifying the DOM for updates while in the middle of a scroll?

Comment 2

[Kartikaya Gupta (email:[e-mail])]

Kevin, would you be able to look into this?

Comment 3

[Kevin Wern]

Sure, I'll look at it tonight.

Comment 4

[Kartikaya Gupta (email:[e-mail])]

Doh. Actually this probably isn't related to APZ scrollbar dragging, because the pref-flip to turn that on was backed out and never landed in Nightly.

Ben, can you double-check what the value of the apz.drag.enabled pref is for you?

Comment 5

[Ben Kelly [:bkelly, not reviewing]]

Oh, huh.  It is false.  Sorry.  I thought I saw it was enabled.

Comment 6

[Kevin Wern]

(In reply to Kartikaya Gupta (email:[e-mail]) from comment #4)
> Doh. Actually this probably isn't related to APZ scrollbar dragging, because
> the pref-flip to turn that on was backed out and never landed in Nightly.

My bad here. I knew about the backout and thought this was odd, but thought I might be missing something and figured I'd test this at home to see if I could reproduce it when false.

Comment 7

[Botond Ballo [:botond]]

Apologies for the confusion. I announced the enablement of async scrollbar dragging on the Nightly channel on dev-platform, but didn't send a follow-up saying it was backed out. I sent one now, so people know it's not actually enabled yet.

Comment 8

[Kartikaya Gupta (email:[e-mail])]

Leaving this in APZ for now although it might need to be moved to layout since that's where the non-APZ scrollbar code lives.

Comment 9

[Kartikaya Gupta (email:[e-mail])]

Also, not clear that this is a regression any more.

Comment 10

[Ben Kelly [:bkelly, not reviewing]]

I can't reproduce on a fresh nightly any more.  Lets call this closed for now.