Textures

Note that this is not official and I am working off a number of assumptions. ~ William Chambers/Bios Element

Creating a Texture

Any image file can be used as a texture, so long as both of its dimensions (height and width) are a power of two: 2, 4, 8, 16, 256, 1024, and so on. World textures are generally 512×512, but you are at liberty to use whatever resolution you see fit. Higher resolutions lower performance but make an image sharper when viewed up close. Bear in mind though that if you go too high, quality may actually degrade because of the amount of resizing required.

Bump map

Note: Ubuntu has a gimp-normalmap plugin in the repo.

Textures often called Bump Maps, or Normal Maps are used to simulate three-dimensional details on a two-dimensional surface by manipulating its lighting. The process is known as Normal Mapping.

Valve Wiki: Normal Map Creation in The GIMP.

Parallax mapping

Parallax mapping (also known as offset mapping or virtual displacement mapping) is a shading technique that displaces the individual pixel height of a surface, so that when you look at it at an angle, the high points will obscure the low points behind them, making it look three-dimensional. The height data for each pixel comes from a heightmap texture, which needs to be created for each parallax mapped material.

Parallax mapping is an enhancement of the bump mapping technique. It is only worthwhile for textures that have a depth of at least a few centimeters, like deep-set bricks or stone.

Valve Wiki: Heightmap.

Reference

See the Cube 2/Sauerbraten docs