4 The definition of will depend on the type of environment map used, because the different projections used by different environment map types (such as spherical, cubic, and azimuth-angle) will cause the relative sampling densities to vary uniquely across the unit sphere. Therefore, to generate a correct result, we need to use the correct solid angle subtended by each texel. The included demo has functions that calculate for both dual-paraboloid and cubic environment maps.