932792 - Drag scroll using the scroll bar results in jitter/shaky scroll

Status: RESOLVED FIXED

(Firefox for Metro Graveyard :: General, defect)

Description

[Srinadh Majji]

User Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:28.0) Gecko/20100101 Firefox/28.0 (Beta/Release)
Build ID: 20131030030201

Steps to reproduce:

Start Firefox in Metro mode and go to any webpage and scroll the page using scroll bar on the right hand side


Actual results:

The scroll is working but the movement is shaky, meaning while scrolling the page and the scroll bar are shaking with small amplitude and high frequency up and down.
P.S. the scrolling with up/down keys and multi-touch gestures is smooth and fine


Expected results:

scrolling must have been smooth, just like in the desktop version  of firefox

Comment 1

[Jim Mathies [:jimm]]

Testing on a surface pro, I also see the scroll thumb jumping around, emulating the jank in the page.

Comment 2

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

I'll look into this.

Comment 3

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

Initial logging indicates that apzc.js is sending us jumpy scroll coordinates in the. APZC is never requesting a repaint (which is expected, since I'm not doing touch-based scrolling), so that's not the cause of jumpiness. It appears to be emanating from somewhere in Gecko. I will dig further.

Comment 4

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

Actually it's not coming from gecko. It's coming from trying to unapply the APZC transform on the input that corresponds to dragging the scrollbar around.

Comment 5

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

Attachment: Treat scrollbars as chrome

The scrollbars were getting treated as content, and so we were unapplying APZ transforms on the mouse events directed to them. As dragging the scrollbar around changes the scroll position and the transform in the APZ code, this could result in crazy hysteresis loops which resulted in the strange behaviour.

Comment 6

[Matt Brubeck (:mbrubeck)]

Comment on attachment 832514 [details] [diff] [review]
Treat scrollbars as chrome

>+            var onScrollbar = false;
>+            for (var node = aEvent.originalTarget; node instanceof XULElement; node = node.parentNode) {

Nit: Use 'let' instead of 'var' on both of these lines.

Comment 7

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

Attachment: Treat scrollbars as chrome

Updated per review comment, carrying r+

Comment 8

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

This should land on fx-team which is currently closed.

Comment 9

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/integration/fx-team/rev/47fcf82de7ab

Comment 10

[:Ms2ger (he/him; ⌚ UTC+1/+2)]

https://hg.mozilla.org/mozilla-central/rev/47fcf82de7ab