The irregular Z-buffer is an algorithm designed to solve the visibility problem in real-time 3-d computer graphics.
It is related to the classical Z-buffer in that it maintains a depth value for each image sample and uses these to determine which geometric elements of a scene are visible.
Its chief disadvantage is that parallel construction of the kd-tree may be difficult, and traversal requires expensive branch instructions.
The grid of lists has the advantage that it can be implemented more effectively on GPU hardware, which is designed primarily for the classical Z-buffer.
In addition to shadow rendering, potential applications include adaptive anti-aliasing, jittered sampling, and environment mapping.