I had a bit of time on my hands, so I decided to play around with XBMC a bit today, setting up dual head on my TV and monitor. I've got a GeForce 8600GT with the official nVidia binary blob installed from the repos on Ubuntu 9.04 64bit and my TV is 32" Philips LCD connected to the computer with a DVI to HDMI cable.

Monster HDMI cables are a scam!

Don't listen to the salesman when he tries to convince you to buy an expensive HDMI cable. Unlike older connection methods, HDMI is a digital signal, so you'll either get a crystal clear picture, or it's going to be really bad. I'm using the cheapest cable I could get which was $8 for 3 metres from MSY and the picture is flawless. The only reason I would buy a more expensive cable would be if I needed thicker insulation to protect against nearby interference, or if I had to run a very long cable, but I would always try the cheaper option first.

Connecting and configuring

After plugging the computer into the TV, I rebooted so the nVidia driver would detect the new screen, then started nvidia-settings form the command line. It can also be started from the System->Preferences menu, but if you do it that way then you can't save any changes you make to your xorg.conf file, because it lives on the root partition, and only the super user can write to it.

gksudo nvidia-settings

There are two options for dual head with nVidia cards, TwinView and a Separate X screen.

TwinView

TwinView doesn't need a reboot to enable, but it came with some significant penalties when I tried it. Both screens had to have the same vertical resolution, and since my desktop monitor has 1024 vertical pixels, versus 1080 on the TV, it caused the bottom border of my desktop window to be about 50 pixels below the bottom of the screen.

That got real annoying, real fast because it meant that I kept over-shooting the Window List on the bottom toolbar when changing applications with the mouse. I also couldn't control which screen was the primary, resulting in my Desktop opening on the TV which is not what I wanted. The third problem was excessive screen tearing in XBMC, which would not respond to enabling vertical syncing in either XBMC or nvidia-settings. This ruled TwinView out of contention.

Separate X Screen

Using a second screen had a number of benefits over TwinView for me. First of all, the second screen could be any resolution, which solved my toolbar problem and secondly, it remembered which screen was the primary. More importantly it solved the tearing problem which made it a pretty clear winner.

The only issue with this procedure is that running XBMC in full screen, using the "-fs" parameter, causes it to grab control of the mouse and keyboard, which means you can't reach the other desktop while it's is running. After some experimentation, I was able to find a fairly simple way to overcome this, which I've documented here.