How do I stop the sky or water being ugly when using texture compression?

Frequently Asked Questions
How do I stop the sky or water being ugly when using texture compression?

This is usually a texture compression problem with all Geforce, Geforce2 and Geforce3 cards including their variants such as the pro, ultra and MX, see the article at GameBasement for more information. Quake3 1.27g onwards corrects the colour 'bleeding' problem when lightmaps are compressed but does not correct the ugly sky or water problem. One solution is to disable texture compression using the Quake3 cvar set r_ext_compress_textures "0" or set r_ext_compressed_textures "0" for 1.27g and above. However this way you lose all texture compression, texture thrashing and other problems may occur. Much better solutions and workarounds follow.

The Nvidia Detonator 6.48 and above driver sets include a workaround for the problem but at this time it is not enabled by default. Locate the registry key for your display device and find the OpenGL entry. Under Windows9x/ME and assuming your card is the only graphics card in your system this is usually HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Class\Display\0000\NVidia\OpenGL , place a dword key called S3TCQuality and set it to the dword value of 1. the full entry is usually as follows

Windows95/98/SE/ME
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Class\Display\0000\NVidia\OpenGL
"S3TCQuality"=dword:00000001

Windows 2000/XP
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\nv4\Device0\OGL_S3TCQuality
"OGL_S3TCQuality"=dword:00000001

If you have more than one display card in your machine or you are running Windows NT or Windows 2000 the registry entry above will be in a different location. Try using a utility such as NVMAX to set the S3TC fix in your registry.

Another solution is to patch the Quake3 executable, download the utility S3TCFixPack and run the executable called Q3S3TCFix, select RGBA S3TC or RGBA4 S3TC as the texture compression type for Quake3. The utility will now save a new executable called Quake3S3TCFix.exe which should be run to correct the texture compression problem with the sky and water.

It should be noted that the Detonator registry and Quake3.exe patch fixes, while correcting the problem reduce compression of textures to 4:1 instead of 6:1