Texture mapping

Texture mapping associates surface locations with values sampled from an image or other texture data. In a common two-dimensional case, each vertex carries coordinates $(u,v)$ identifying a location in the texture. Rasterization interpolates the coordinates, and a fragment shader uses them to obtain a color or another surface parameter.^[ref]

For example, a square wall can use $(0,0)$, $(1,0)$, $(1,1)$ and $(0,1)$ at its corners so a rectangular image covers it once. Repeating coordinates from zero to four can tile the same image when the wrapping mode allows repetition. The mapping is separate from sampling: nearest-sample selection and interpolation can give visibly different results from identical coordinates.

When a tilted surface is viewed through perspective projection, equal distances on the surface need not occupy equal distances on screen. Correct interpolation must account for that projection. A texture also supplies data rather than an automatic physical material model: a stored color and the light reflected toward the camera are different quantities.