Recently I had some troubles with my Doom 3 game being f*cked up a little. One of the issues was, that the resolution has been reset to 640×480 pixel and I could only change it back to 1024×768 pixel the max.

However, I was able to fix it and playing in pretty widescreen again. Here is what you need to do for your custom screen settings:

The following 4 parameters from within your DoomConfig.cfg-file are important:

• r_customHeight
• r_customWidth
• r_aspectRatio
• r_mode

Here is an example from my own config, set to 16:9 widescreen with 1280×800 pixel:

seta r_customHeight "800"
seta r_customWidth "1280"
seta r_mode "-1"
seta r_aspectRatio "1"

The value “r_aspectRatio” can be set to…

• “0″ for 4:3
• “1″ for 16:9
• “2″ for 16:10

“r_mode” set to -1 tells the game to use the values for r_customHeight and r_customWidth.

References used

Doom 3 Resurrection – widescreen support?
Doom 3 Tweak Guide