SCHMALSTIEG D.: On-the-fly generation and rendering of infinite cities on the GPU

Figure 1: Infinite cities with highly detailed, context-sensitive buildings can be generated in real-time on the GPU using a parallel shape grammar. The visible 28km2 of the city contain up to 47000 buildings. In full detail, these buildings would expand to 240 million rules, producing 2 billion triangles. Generating an initial view with adaptive level of detail (7 million triangles) from scratch takes 500ms. Exploiting frame-to-frame coherence, we update the geometry for successive frames in 50ms on a standard PC, even if the viewer moves at supersonic speed. In this paper, we present a new approach for shape-grammar-based generation and rendering of huge cities in real-time on the graphics processing unit (GPU). Traditional approaches rely on evaluating a shape grammar and storing the geometry produced as a preprocessing step. During rendering, the pregenerated data is then streamed to the GPU. By interweaving generation and rendering, we overcome the problems and limitations of streaming pregenerated data. Using our methods of visibility pruning and adaptive level of detail, we are able to dynamically generate only the geometry needed to render the current view in real-time directly on the GPU. We also present a robust and efficient way to dynamically update a scene’s derivation tree and geometry, enabling us to exploit frame-to-frame coherence. Our combined generation and rendering is significantly faster than all previous work. For detailed scenes, we are capable of generating geometry more rapidly than even just copying pregenerated data from main memory, enabling us to render cities with thousands of buildings at up to 100 frames per second, even with the camera moving at supersonic speed