The bottom line on what happens on each card is as follows.Īll modern NVIDIA and all ATI hardware use the compressed normal maps in Medium and Low qualities with the swizzled components. This effectively allows the compression to do a much better job and is just one extra instruction in the fragment program to move the alpha channel into the red channel. ATI had done some research on various methods of normal map compression and we ended swapping the red and alpha ( which is zero in the case of a normal map ) channels. ATI does not support the palettized compression so we needed a better solution. Unfortunately this compression does a poor job in other cases and you end up getting splotchy areas. NVIDIA hardware supports palettized compression which yields good compression and normal maps retain hard and round edges really well.
One thing of note on the normal map compression is that generally speaking if you DXT a normal map you get really crappy results.
Low quality does everything medium quality does but it also downsizes textures over 512x512 and we downsize specular maps to 64圆4 in this mode as well. This level gets us comfortably onto 128 MB video cards. This still looks really really good but compressing the normal maps can produce a few artifacts especially on hard angled or round edges. Medium quality uses compression for specular, diffuse, and normal maps. This is the quality that for instance the PC Gamer review was played in. This looks very very close to Ultra quality but the compression does cause some loss. High quality uses compression ( DXT1,3,5 ) for specular and diffuse and no compression for normal maps. It does however look fantastic :-) and it is certainly playable on high end systems but due to the hitching that can occur we chose to require a 512 MB Video card before setting this automatically. This can cause some choppiness as a lot of memory bandwidth is being consumed. This will run on current hardware but obviously we cannot fit 500 MB of texture data onto a 256 MB card and the amount of texture data referenced in a give scene per frame ( 60 times a second ) can easily be 50 MB+.
In a typical DOOM 3 level, this can hover around a whopping 500 MB of texture data. In Ultra quality, we load each texture diffuse, specular, normal map at full resolution with no compression. Image fidelity is dependent on what quality level we load the textures at.
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