1111957 - [e10s] Dragging e10s window between HiDPI and non-HiDPI displays causes text to be scaled incorrectly (again)

Status: RESOLVED FIXED

(Core :: Graphics: Text, defect)

Description

[Chris Peterson [:cpeterson]]

+++ This bug was initially created as a clone of Bug #978913 +++

HiDPI bug 978913 is back:

I have a Retina MacBook Pro with a non-HiDPI external display. When I drag an e10s window from the external display to the MacBook Pro's Retina display, the page text becomes very tiny. If I drag an e10s window from the Retina display to the external display, the page text becomes very large.

I believe this is a regression in Nightly 37 build 2014-12-13:

https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=5288b15d22de&tochange=f14dcd1c8c0b

Unfortunately, mozregression is unable to accurately bisect a narrower regression range.

* Fabrice: could your sync getDPI() changes for FxOS bug 1107259 have affected the desktop browser when e10s is enabled?

Comment 1

[[:fabrice] Fabrice Desré]

That's very possible, yes. We cache the dpi more aggressively now. We should be able to force a "reset" when moving to another display I guess.

Comment 2

[Mike Conley (:mconley) (:⚙️)]

I *think* this is a matter of clearing out the mDPI and mDefaultScale members in TabChild::RecvUIResolutionChanged. I'll see if that helps.

Comment 3

[Mike Conley (:mconley) (:⚙️)]

Clearing mDPI and mDefaultScale seemed to fix the regression. Patch coming up.

Comment 4

[Mike Conley (:mconley) (:⚙️)]

Attachment: Invalidate mDPI and mDefaultScale in TabChild when switching displays. r=?

Bug 1107259 made TabChild cache the display DPI and default scale more aggressively, and
we need to invalidate those caches when switching displays, otherwise we can get weird
scaling behaviours when switching between displays with different DPIs and scales.

Comment 5

[Dan Mosedale (:dmosedale, :dmose)]

FWIW, the regression occurred within the last week or so.

Comment 6

[Mike Conley (:mconley) (:⚙️)]

Thanks!

remote:   https://hg.mozilla.org/integration/fx-team/rev/769664485cdb

Comment 7

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/769664485cdb