OpenGL directly supports environment mapping using spherical environment maps. A sphere map is a single texture of a perfectly reflecting sphere in the environment where the viewer is infinitely far from the sphere. The environment behind the viewer (a hemisphere) is mapped to a circle in the center of the map. The hemisphere in front of the viewer is mapped to a ring surrounding the circle. Sphere maps can be generated using a camera with an extremely wide-angle (or fish eye) lens. Sphere map approximations can also be generated from a six-sided (or cube) environment map by using texture mapping to project the six cube faces onto a sphere.
OpenGL provides a texture generation function (GL_SPHERE_MAP) which maps a vertex normal to a point on the sphere map. Applications can use this capability to do simple reflection mapping (shade totally reflective surfaces) or use the framework to do more elaborate shading such as Phong lighting [95]. Applications of environment mapping are discussed in Sections 10.4 and 11.2.1.