I have a triple display setup with two 1080p monitors and a third 4:3 one, and I had some free time to kill, so I decided to give Doom3 BFG edition a try. The problem is that, for me it started full screen in a display that I didn’t want to play on, and in a screwed up resolution. As there are no helpful options in the settings menu, it was tricky to solve this issue, but finally I managed to fix it. So if you have this problem, here is the way to solve it:

1. Open the D3/BFGConfig.cfg located in your user’s home folder Saved Games/id Software/DOOM 3/BFG/base in a text editor.
2. Look for the line r_fullscreen. It is initially set to 1. By changing it to 2 or 3, you are able to move the game to different displays.
3. Now to fix the resolution, first change r_vidMode to –1, and then set the values of r_customHeight and r_customWidth to your desired resolution. In my case the settings are:

set r_customHeight “1080”
set r_customWidth “1920”
set r_fullscreen “2”
set r_vidMode “-1”