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From surface shaders that determine how surface parameters and scene parameters are combined to produce color, to algorithms that organize scene objects in an efficient manner, the choice of a lighting and shadowing algorithm often has the single greatest impact on the design of your rendering engine. Choosing an algorithm influences more than just the look of your scenes: it affects the way content is authored and how complex and interactive your scenes can be. The chapters in this part of the book describe various algorithms for lighting and shadowing, along with techniques for making these algorithms more efficient and robust.
In Chapter 9, "Effective Shadow Volume Rendering," Morgan McGuire thoroughly covers the popular stencil shadow volume technique for rendering real-time shadows. Stencil shadow volumes, although often simple to implement initially, are notoriously difficult to make robust and fast. This chapter focuses on getting the corner cases right and reducing the geometry and fill-rate costs of the technique.
Fabio Pellacini and Kiril Vidimce, in Chapter 10, "Cinematic Lighting," present a general lighting shader based on a shader used by Pixar Animation Studios but simplified for real-time lighting. This uberlight shader, as it is known, was written with the fundamental goal of giving control over as many lighting parameters as possible to the artist lighting the scene.
One of the most popular general real-time lighting algorithms today is shadow maps. A major issue that arises when using shadow maps is aliasing. In Chapter 11, "Shadow Map Antialiasing," Mike Bunnell and Fabio Pellacini describe how to reduce shadow map aliasing efficiently through percentage-closer filtering.
Chapter 12, "Omnidirectional Shadow Mapping" by Philipp S. Gerasimov, extends the shadow map idea to correctly handle omnidirectional (point) light sources. Implementation details, including fallbacks depending on hardware capabilities, are included.
Most shadows in real-time games are hard-edged and aliased, due to their being approximated as simple point lights without area. In the real world, all lights have nonzero area, and therefore all shadows have varying degrees of softness. In Chapter 13, "Generating Soft Shadows Using Occlusion Interval Maps," Will Donnelly and Joe Demers introduce a new technique for accurately rendering soft shadows in static scenes with lights that move along predetermined paths. This technique was used in the NVIDIA GeForce FX 5900 launch demo, "Last Chance Gas."
Simon Kozlov continues the antialiasing crusade in Chapter 14, "Perspective Shadow Maps: Care and Feeding." He presents new ideas on optimizing perspective shadow maps, a new kind of shadow map introduced by Stamminger and Drettakis at SIGGRAPH 2002. Perspective shadow maps strive to reduce or eliminate shadow map aliasing artifacts by maximizing shadow map texel density for objects that are projected to large pixel areas.
Finally, in Chapter 15, "Managing Visibility for Per-Pixel Lighting," John O'Rorke observes that techniques that increase visual complexity also tend to increase the number of batches being sent to the hardware—a crucial metric to minimize if you want to get the best performance out of modern GPUs. This chapter uses a number of visibility techniques to find an optimal set of batches to submit, resulting in large performance gains. The techniques have the nice side effect of reducing both CPU load and GPU load.
Cem Cebenoyan, NVIDIA
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