1371299 - Scrollbar thumb inside iframe flickers after being offscreen

Status: VERIFIED FIXED

(Core :: Panning and Zooming, defect, P2)

Description

[ovidiu boca[:Ovidiu]]

This issue is reproducible only on Windows. Tested on Windows 7 and 10 with FF Nightly 55.0a1(2017-06-08) 

STR:
  1. Load https://people-mozilla.org/~bballo/bug1359868.html
  2. Unmaximize the Firefox window if necessary, and position it
     so that there's space below it.
  3. Click on "Append"
  3. Grab the subframe's scroll thumb near the top.
  4. Drag it down until mouse leaves the Firefox window, and then back up.

Expected results:

  The scrollbar thumb is fully painted when you drag it back up.

Actual results:

  The scrollbar thumb has some flickers.

Comment 1

[Botond Ballo [:botond]]

Thanks, I can reproduce this on Windows.

Comment 2

[Botond Ballo [:botond]]

This appears to be a regression from bug 1352863. The bug can be reproduced on other platforms after setting the "slider.snapMultiplier" pref to a non-zero value (Windows builds use 6) and restarting.

Comment 3

[Botond Ballo [:botond]]

We are snapping back the thumb to its original position whenever we think the mouse is horizontally (for a vertical thumb) farther away from it then a constant multiple times the thumb width. When the thumb is offscreen, the width computed in APZ is zero, so the condition is triggered spuriously.

Comment 4

[Botond Ballo [:botond]]

Attachment: Bug 1371299 - Restrict the thumb snapping back to its original position to when the thumb is on-screen

Old school patch because MozReview is not being cooperative.

Comment 5

[Botond Ballo [:botond]]

Attachment: Bug 1371299 - Restrict the thumb snapping back to its original position to when the thumb is on-screen

Now without silly grammar errors.

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/091c8103ff38
Restrict the thumb snapping back to its original position to when the thumb is on-screen. r=kats

Comment 7

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

https://hg.mozilla.org/mozilla-central/rev/091c8103ff38

Comment 8

[ovidiu boca[:Ovidiu]]

I verified this issue on Windows 10 and 7 with FF Nightly 56.0a1(2017-06-13) and I can't reproduce the bug. I will mark as a verified fix.