MegaTexture is probably the most well known improvement that ETQW will have over DOOM 3. The 32,000 by 32,000 6GB source texture you mentioned in previous interviews suggests you're not using any procedural textures at run-time but considering the multiple DVDs implication, are the .MEGA files compressed, and if so, are you compressing by tile or as a whole (single file)?

Enemy Territory: QUAKE Wars features a tool suite for creating MegaTextures called MegaGen. Once the Artist or Level Designer has completed the artwork, MegaGen outputs two entirely unique 4GB textures - a diffuse map containing colour data, and a normal map - and then combines them into a single 5GB data file. This data file is then split into unique tiles suitable for streaming, and then compressed to reduce disk space usage. The resulting unique MegaTexture is around 500MB in size. This represents a reasonable tradeoff between ETQW's visual quality and disk space usage (maintaining a shippable size for the game).
 

Does MegaTexture require any sort of custom fragment program to render? If so, could you tell us how complex it is in terms of instruction count/texture reads? How does it compare to the other fragment programs you use?

The low level ETQW rendering engine has moved on a fair bit since Doom 3. The fixed function pipeline has been dropped, resulting in a pure shader-based renderer. The MegaTexture shaders are a set of special case version of our normal ones which deal with ambient lighting, normal light interaction and the other stages in our pipeline. They are some of the more expensive ones in the game, and fairly heavy on texture reads. Depending on the target hardware, some of the texture lookups get replaced by ALU instructions to improve performance.