Comment 0 for bug 146859

Scenario:

Toshiba L20 laptop, with builtin 1024x768 builtin LCD, Intel i915 graphics card.
External monitor of 1280x1024 resolution

Using the default configuration (after dpkg-reconfigure -phigh xserver-xorg):

mteira@sombra:~$ xrandr -q
Screen 0: minimum 320 x 200, current 1024 x 768, maximum 1024 x 1024
VGA disconnected (normal left inverted right)
LVDS connected 1024x768+0+0 (normal left inverted right) 304mm x 228mm
   1024x768 60.0*+
   800x600 60.3
   640x480 59.9
TV disconnected (normal left inverted right)

With this default configuration, the maximum width (1024) is not enough for a multimonitor mode using my two monitors (1024 + 1280), so, I changed my Display Screen subsection to:

        SubSection "Display"
                Modes "1024x768"
               Virtual 2304 1024
        EndSubSection

After this, I'm able to setup a multimonitor mode using randr, but DRI is no longer available. I'm getting this log:

(EE) intel(0): Cannot support DRI with frame buffer width > 2048.

So, no compiz, no google-earth, no fancy screensavers,...

I've found this thread where it seems that the coordinate registers for the 3D engine are only 11 bits:
http://lists.freedesktop.org/archives/xorg/2007-June/025501.html

BTW, I tested a hacked OSX version on this box some time ago, and it was able to operate Quartz Extreme with both screens at the same time without problems. Probably the screen/display design could be the problem? I find it frustrating, as with a relatively new graphics card I'm not able to use two monitors (with a not that high resolution) and hardware accelerated display at the same time.