Ok. When xrandr turns off the LVDS display, the *only* thing it does is set the LVDS' CRTC to "off".
Tracing through gnome-desktop's RANDR code, on the other hand, we have: 0) Grab the server 1) First, set all CRTCs to off. 2) Now, foreach output, assign the first valid CRTC to it 2*) If some outputs did not have a valid CRTC, bail 3) Set each CRTC to the appropriate mode, attached to the appropriate output 4) Ungrab the server. This would appear to have two results: 1) gnome-desktop can reject valid setups should there be a CRTC with restrictions on which outputs it can drive (which is extremely common), and 2) gnome-desktop does a whole lot of unnecessary work on modeswitch. Somewhere in that extra work, something is going wrong. I'm not entirely sure what it is, though. One of the side-effects is that disabling the LVDS will cause gnome-desktop to drive the external display with a different CRTC, but xrandr happily switches between different CRTCs on my external display… -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to xserver-xorg-video-intel in Ubuntu. https://bugs.launchpad.net/bugs/861426 Title: [Oneiric] [Regression] When disabling onboard LVDS display and just using external VGA screen corruption occurs To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/861426/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp
