My professional involvement in hardware-accelerated computer graphics began 15 years ago, and I am keenly aware of where our industry came from and how far we've evolved. In 1988, most workstation users would have considered themselves extremely fortunate to have a system with a hardware-accelerated z-buffer, not to mention something that supported even the most primitive form of lighting. On the other hand, once texture mapping and Phong lighting hardware acceleration appeared a couple of years later, what followed was more of an evolution in cost reduction and large-scale integration, not a functional revolution. In fact, up until one or two years ago, almost all games used at most a Phong lighting model, modulated with layers of textures.
Nevertheless, today we are seeing a virtual explosion of complex lighting and surface reflection models in real-time graphics research and in game demos, pushing the technological envelope. These techniques include high-dynamic-range environmental lighting and preconvolved diffuse maps, separable bidirectional reflectance distribution functions (BRDFs), and many techniques using depth and occlusion information to render more accurately all varieties of materials—transparent, translucent, or opaque. This part of the book covers a number of these techniques.
In Chapter 16, "Real-Time Approximations to Subsurface Scattering," Simon Green describes several different methods of approximating the look of translucent materials, such as skin and marble, using programmable graphics hardware.
Next, in Chapter 17, "Ambient Occlusion," Matt Pharr and Simon Green show how to combine the preprocessing of occlusion information of an object and its environment with an efficient real-time shader that takes these elements into account to create a realistically lit and shadowed object.
David McAllister presents an interesting approach to representing multiple complex materials by encoding separate BRDFs within a single texture map, in Chapter 18, "Spatial BRDFs." He then expands upon this notion to support discrete lights as well as environmental lighting.
In Chapter 19, "Image-Based Lighting," Kevin Bjorke breaks out of the standard cube-map environment and delves into a world with many more possibilities for realistic lighting effects. First he explores image-based lighting, including localized cube maps—the analogue of local lighting using image-based rendering—then he shows how to apply those critical final touches to the shading model, including realistic reflectance, shadows, and diffuse/ambient terms.
Finally, in Chapter 20, "Texture Bombing," Steve Glanville shows how texture bombing and related cellular techniques can add a visual richness to your shaders, amplifying the variability of your images and reducing the repetitive look of large textured regions. He concludes with an interesting exposition on developing Voronoi diagrams within a pixel shader, which could serve as the kernel of a broad spectrum of shaders depicting natural phenomena, including scales, bubbles, leaves, and skin.
John Spitzer, NVIDIA
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