Texture mapping

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Spherical texture mapping

Texture mapping is a method, invented by Ed Catmull, of adding detail, surface texture, or colour to a computer-generated graphic or 3D model. A texture map is applied (mapped) to the surface of a shape. This process is akin to applying gift wrapping paper to a plain white box. In the example at right, a texture map of the Earth's coloration is applied to a sphere to create the illusion of color detail that would take very many additional polygons to realise otherwise. This kind of coloration is the most common application of texture mapping.

Multitexturing is the use of more than one texture at a time on a shape^{[citation needed]}. This has various uses, sometimes as a way of applying a light map to a surface, which is faster than requiring the graphics hardware to do lighting calculation for that surface on the fly, or more recently bump mapping has become popular, which allows a texture to directly control the lighting calculations, allowing the surface to not only have detailed colouring, but detailed contours as well (bumps)(unclear).

The way the resulting pixels on the screen are calculated from the texels (texture pixels) is governed by texture filtering. The fastest method is to use the nearest neighbour interpolation, but bilinear interpolation is commonly chosen as good tradeoff between speed and accuracy.

At the hardware level usually texture coordinates are specified at each vertex of a given triangle (any polygon may be broken down into triangles for rendering), and these coordinates are interpolated as part of a calculation that is an extension of Bresenham's line algorithm. Direct interpolation of the texture coordinates between vertices results in affine texture mapping, which causes a perceivable discontinuity between adjacent triangles when the 3D geometry of the specified triangle is at an angle to the plane of the screen, perspective correction is thus preferred where realism is important, and adjusts the texture coordinate interpolation as a function of the 3D depth of each pixel. Because perspective correction involves slightly more calculation it negatively affects performance speed^{[citation needed]}.