unity has issues with intel gen3 hardware in 2 screens configs

[Sergio Callegari]

Unity in Raring has an issue with intel gen3 graphics hardware. When a second screen is connected (e.g. an external monitor or projector is connected to a laptop), unity/compiz crashes and the machine remains alive but almost useless.

This makes it impossible to give presentations with a projector with many small laptops with intel gen3 graphics hardware.

Using 2 screens on gen3 was possible till not long ago with unity, so this bug is a regression.

The reason for the issue has already been found, here is a brief discussion. See also https://bugs.freedesktop.org/show_bug.cgi?id=67846.

Gen 3 hardware can only support screens when the size is less than 4096x4096. However it can only support GL framebuffer objects as wide as 2048x2048. As a matter of fact, software workaround were attempted to rise this to 4096x4096 but they are currently broken. This means that unity on two screens can be supported as long as the overall size of the two screens is within 2048x2048. Fitting in that limit is by no means hard if the two screens are arranged one above the other with xrandr. This is quite true for small laptops that often only have a 600 pixels vertical resolution.

Unfortunately, the latest unity tries to autoconfigure thing when a second screen is attached by automatically putting it on the side of the original screen. With this the overall size of 2048x2048 is easily exceeded, the GL fbo cannot be allocated and compiz crashes.

IMHO opinion there are 2 points that should be addressed

1) Compiz/Unity should never crash. If the GL cannot provide what is needed when the second screen is attached, unity should not crash, but in the worst case at least fall back to a single screen config, ignoring the external monitor, thus leaving the machine in a usable state

2) When attaching a second monitor, unity should either:
- not try to much magic. Ask the user what to do, and how to configure the screens; or
- include a table of quirks so that it knows that certain setups are not possible and avoid them. For instance when gen3 hardware is detected it should know that the overall size with two monitors must fall within 2048x2048 and organize the screens accordingly if possible (e.g. one above the other) or leave the external monitor unconfigured if impossible.

[Christopher Townsend (townsend)]

Hi Sergio,

Could you do an "apport-collect 1209261" so we can get logs and the crash to help figure out where/why Unity/Compiz is crashing?

I looked at the commits for Unity and don't think it's anything in Unity itself causing this. However, there is a commit in Compiz that looks like it may have some effect: http://bazaar.launchpad.net/~compiz-team/compiz/0.9.9/revision/3655

Thanks!

[Launchpad Janitor (janitor)]

[Expired for unity (Ubuntu) because there has been no activity for 60 days.]