Interactive summed-area table generation for glossy environmental reflections

There are many applications in computer graphics where spatially varying filters are useful. One example is the rendering of glossy reflections. Unlike perfectly reflective materials, which only require a single radiance sample in the direction of the reflection vector, glossy materials require integration over a solid angle. Blurring by filtering the reflected image with a support dependent on the surface‘s BRDF can approximate this effect. This is currently done by pre-filtering off-line, which limits the technique to static environments. Crow [1984] introduced summed-area tables to enable more general texture filtering than was possible with mip maps. Once generated, a summed-area table provides a means to evaluate a spatially varying box filter with a constant number of texture reads.