1281042 - Displayport expiry can result in perma-checkerboarding

Status: RESOLVED INCOMPLETE

(Firefox for Android Graveyard :: Toolbar, defect, P3)

Description

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

+++ This bug was initially created as a clone of Bug #1280013 +++

Load something like https://treeherder.mozilla.org/#/jobs?repo=try&revision=f615a14b2c7b&group_state=expanded&selectedJob=22404671 in desktop mode in Fennec. Make sure the error pane down below is scrollable. Zoom in so that the error pane occupies most of the visible space, and scroll it. Then wait 15s for the displayport on the subframe to expire. When this happens, the displayport on the root content document is also removed and re-added, but it gets reset back to 0,0. This results in visible perma-checkerboarding.

The displayport getting removed and re-added is intentional, from the code at [1]. However it doesn't account for the fact that in some cases (e.g. overflow:hidden but zoomable documents) there is a persistent callback transform that shifts the displayport from the composition bounds. When the displayport is removed and re-added the new version doesn't have the callback transform, and so it gets reset back to 0,0.

It's kind of an edge case but shouldn't be too hard to fix.

[1] http://searchfox.org/mozilla-central/rev/970569ad57ac4436ff31aa2ac63f38ed3ee2932d/layout/generic/nsGfxScrollFrame.cpp#2434

Comment 1

[BMO Automation]

We have completed our launch of our new Firefox on Android. The development of the new versions use GitHub for issue tracking. If the bug report still reproduces in a current version of [Firefox on Android nightly](https://play.google.com/store/apps/details?id=org.mozilla.fenix) an issue can be reported at the [Fenix GitHub project](https://github.com/mozilla-mobile/fenix/). If you want to discuss your report please use [Mozilla's chat](https://wiki.mozilla.org/Matrix#Connect_to_Matrix) server https://chat.mozilla.org and join the [#fenix](https://chat.mozilla.org/#/room/#fenix:mozilla.org) channel.