[Wylug-help] Desktop Spanning Multiple Screens

[John Hodrien]

On Mon, 13 Jul 2009, Smylers wrote:

> I'm running Ubuntu 9.04, with Gnome 2.26.1.  In 'Display Preferences'
> some configurations with an unmirrored external monitor cause it to
> prompt for root privs to change some system setting, which so far as I
> can tell is simply tweaking xorg.conf to have SubSection "DIsplay" with
> the Virtual setting, as described here:
>
>  http://209.85.229.132/search?q=cache:http://intellinuxgraphics.org/dualhead.html&strip=1
>
> That page includes the comment:
>
>  # There is a known issue that DRI doesn't work on pre-965 if maximum
>  # is larger than 2048x2048.
>
> Indeed configurations with my 1280×800 laptop next to a 1024×768 monitor
> (2304 pixels wide) cause nothing meaningful to display the next time I
> log into X.  Configuring my laptop as only 1024×768 (so it has black
> margins) works, as does arranging the displays vertically.

Well that's pants.

> So I'm guessing that that limit applies to me and there's nothing I can
> do about it -- more specifically that 'DRI' is some technology necessary
> for what I'm trying to do, and that '965' is a chip number and it's
> newer than the 'Mobile 945GM/GMS, 943/940GML Express Integrated Graphics
> Controller' which lshw reports this laptop as having?

945 is definitely less capable than 965.

You should be able to disable DRI and see what gives.  I believe it's:

Option "DRI" false

in the device section of your xorg.conf.  Could be worth seeing what it does
in a single monitor setup.

DRI certainly isn't required for a normal 2D desktop, so I wouldn't expect
this sort of problem.  Anything exciting output in the logs when you do that?

I'm unfamiliar with multi-display with intel.  What you typically see with
nVidia is that there's a 4096x4096 pixel limit on hardware accelerated OpenGL
(which I figure links into the DRI reference).  You can actually have a
desktop as big as you like, and as long as a *window* is smaller than that,
hardware acceleration works just fine.

jh