The Absolutely Definitive guide to tweaking Doom3 for Ati graphics card systems...

Using these tweaks I went from 5fps on the opening sequence on an Ati Radeon 9800 pro (doom3, highquality, 2x) to 40fps (same settings). 'Nuff said.

• Optimise your system: There are a million guides on the net on how to do this. Google and use them.
• Catalyst 4.9 beta or later: Install these drivers. I've used these without any signs of instability or crashing. Most people report a 4-5fps increase, particularly those with newer ati chipsets.
• Rage3D tweaker: Download from www.rage3d.com. Turn on: 3Dnow for AMD systems, SSE for Intel Pentium 3 systems, SSE *and* SSE2 for Intel Pentium 4 or higher systems (this makes a *huge* difference). Turn on triple-buffering. Turn on anything else that looks fast.
• Antialiasing: There is a general concensus that because Doom3's internal edges are already smoothed via pixel shaders, there is less need for full-screen anti-aliasing than other games - plus, this takes a huge performance hit. Turn anti-aliasing down to a level that seems aesthetically acceptable to you (as an example, for me this is 2x, in other game's it would be 6x).
• Fast antialiasing: If you're already on 2x antialiasing and don't feel like you need even that much, go into regedit, search for OGLEnableFastFullSceneAA - set to '1' every time you find it. This switches on a faster, less expensive antialiasing mode at a small loss of quality - I almost would call it '1.5x antialiasing'.
• The Ati shader tweak: For some reason there is a shader which appears to do some unnecessary operations, which in particular affects ati performance. Download the re-written for ati shader from here and install as per instructions. About a 5-fps increase.
• Config file tweaking: go into the doom3/base directory, edit doomconfig.cfg and do the following:
  seta image_useCache - set to "1"
  seta image_cacheMegs - set to quarter or half of your total system ram, in megabytes (eg. "256" for 512MB memory systems).
  seta image_cacheMinK - set to "20480"
  seta com_videoram - set to the amount of memory on graphics card, in megabytes (e.g "128").
  These tweaks should stop in-game pauses, also possibly speed up fps's
• Dual displays: There is a performance hit if you're using dual (or more) displays when playing doom3 - to disable these, the fastest way is to turn on the 'single mon. in games' option in rage3d tweaker (game utils->per game options->single mon. in games). The other way is just to disable the secondary monitor in your display settings (display properties->settings->select secondary monitor, untick 'extend my windows desktop onto this monitor').
• The .pk Unpacking trick... People from ID software said this won't work. It does, for the majority of systems - it may not speed up save-game or level loadtimes on -all- systems, but the general consensus is that it reduces or removes the funny pauses you get ingame when going into a new room or section. Download winrar or any RAR-equivalent (apparently this works with winzip as well, though I haven't tried it). Use it to unpack all of the .pk files into the doom3/base directory. Then move the .pk files to another directory, or delete them. The reasoning behind this, I would imagine, is that when loading a small section or a couple of new shaders, it doesn't have to search through the compressed-file structure to find it. Warning: This destroys multiplayer, if you're into that.
• Overclocking: Wasn't worth it on my card but, do it if you want to, don't blame me if anything fries. Go to guru3d, search for and download 'atitool', use it to find the top values you can overclock your memory and GPU to, then set these values using rage3d.

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