Ultra Shadow Technology
Programmers can define a subset of the scene (within z-min and z-max) to limit lighting/ shadow calculations to the appropriate area for each light source.
Modern games use "stencil shadows" to calculate shadows (for more info, see www.gamedev.net ). One upcoming game that will make extensive use of such shadow calculations is the highly anticipated Doom III (exclusive benchmarks later on in this article!). The complexity of rendering shadows takes its toll on game performance, though, dragging down the frame rate. Enter NVIDIA's "UltraShadow." This feature allows a game developer to specify in what parts of the scene a shadow will be visible and in which it won't, thereby preventing unnecessary calculations. This, in turn, will allow designers to define more complex shadows in other parts of the scene. NVIDIA calls this technique "shadow culling."
A special Wireframe mode in the game Abducted causes the geometry needed for the shadow volumes to become visible.
One of the advantages of the GeForceFX GPU is its ability to render volume shadows in one pass thanks to two-sided stencil support, while other GPUs require two passes for this type of calculation. Shadow culling should boost this feature even further.