On a more modern CPU, we can expect this number to be between 30,000 and 120,000 batches per second (around 1,000 to 4,000 batches per frame at 30 frames/sec). Wloka 2003 shows that a 1 GHz CPU can render only around 10,000 to 40,000 batches per second in Direct3D. Submitting triangles to the GPU for rendering in Direct3D is a relatively slow operation. Figure 3-1 shows an example from Black & White 2, a game in development at Lionhead Studios.įigure 3-1 Geometry Instancing in Black & White 2 3.1 Why Geometry Instancing? This chapter addresses the problem of rendering many unique instances of the same geometry in Direct3D. Graphics APIs such as Direct3D and OpenGL are not designed to efficiently render a small number of polygons thousands of times per frame (Wloka 2003). However, rendering a large number of small objects, each made from a few polygons, imposes a big strain on today's GPUs and rendering libraries. The user perceives a forest made of many unique trees and believes the world to be credible, enriching his or her game experience. For example, every tree in a big forest might be geometrically very similar, but all may be different in terms of their color or height. From countless blades of grass, to trees, to generic clutter: it all improves the final perception and helps maintain the user's "suspension of disbelief." If the user can believe the world he is immersed in, he is more likely to be emotionally connected to that world-the Holy Grail of game development.įrom a rendering point of view, achieving this richness translates into rendering many small objects, often each one similar to the next, with only small differences such as color, position, and orientation.
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The CD content, including demos and content, is available on the web and for download.Ī great way to enrich the user experience in an interactive application is to present a credible world, full of small, interesting features and objects. You can purchase a beautifully printed version of this book, and others in the series, at a 30% discount courtesy of InformIT and Addison-Wesley. GPU Gems 2 GPU Gems 2 is now available, right here, online.
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