Lightmap

A lightmap is a data structure used in lightmapping, a form of surface caching in which the brightness of surfaces in a virtual scene is pre-calculated and stored in texture maps for later use. Lightmaps are most commonly applied to static objects in realtime 3d graphics applications, such as video games, in order to provide lighting effects such as global illumination at a relatively low computational cost.

John Carmack's Quake was the first computer game to use lightmaps to augment rendering. Before lightmaps were invented, realtime applications relied purely on Gouraud shading to interpolate vertex lighting for surfaces. This only allowed low frequency lighting information, and could create clipping artefacts close to the camera without perspective-correct interpolation. Discontinuity Meshing was sometimes used especially with radiosity solutions to adaptively improve the resolution of vertex lighting information, however the additional cost in primitive setup for realtime rasterization was generally prohibitive. Quake's software rasterizer used surface caching to apply lighting calculations in texture space once when polygons initially appear within the viewing frustum (effectively creating temporary 'lit' versions of the currently visible textures as the viewer negotiated the scene).

As consumer 3d graphics hardware capable of multitexturing, light-mapping became more popular, engines began to combine light-maps in realtime as a secondary multiply-blend texture layer.

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