Login screen forces same resolution on all displays in non-identical multi-display setup

[Bruno Girin]

In a multi-display setup where displays have different resolutions (e.g. external display connected to laptop), the login screen forces the same resolution on both displays. For example in my setup I have a laptop with a 16:9 ratio and an external screen with a 4:3 ratio. The background appears on both displays and the login box appears on the laptop's built-in display. However, both displays are forced to a 4:3 resolution that only fits the external screen.

Steps to reproduce:
1. Connect an external display to a laptop with different ratio (e.g. 16:9 laptop and 4:3 external display)
2. Start the laptop
3. The login screen appears

Expected behaviour:
Each display shows an image that is scaled according to their individual resolutions

Actual behaviour:
Both displays are forced to a degraded resolution that can be displayed by both. E.g. in my case the laptop has a max resolution of 1366x768 while the external display has a max resolution of 1280x1024: the resolution used by the login screen is 1024x768 i.e. a 4:3 resolution (like the external display) but with 768 vertical resolution (which is the max vertical resolution of the laptop).

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: lightdm 1.2.1-0ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-24.37-generic 3.2.14
Uname: Linux 3.2.0-24-generic x86_64
ApportVersion: 2.0.1-0ubuntu7
Architecture: amd64
Date: Fri May 11 21:46:20 2012
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Beta amd64 (20110901)
ProcEnviron:
 LANGUAGE=en_GB:en
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: lightdm
UpgradeStatus: Upgraded to precise on 2012-02-11 (90 days ago)

[Bruno Girin (brunogirin)]

Note that this bug may be related to bug #997803 which occurs with the unlock screen.

[Tobias Schaible (tobi1711)]

Same here. My laptop (1366x768) and my external display (1920x1080) have got a 16:9 resolution. On my laptop display it is shown in a 4:3 resolution with black borders on both sides. On the external display it is shown in the same resolution like on the laptop display, but fullscreen.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Sebastien Bacher (seb128)]

Thank you for your bug report, what greeter do you use, the unity one? (default in Ubuntu). Does it "fixes" itself if you reconnect the external monitor? It seems a duplicate of bug #959592

[Bruno Girin (brunogirin)]

Hi Sebastien, it is the default Ubuntu greeter. Disconnecting and re-connecting the external display while on the greeter fixes the problem (at least temporarily, I haven't rebooted yet).