Interactive Vegetation Rendering

Vegetation poses a significant problem to computer graphics because the geometric complexity of plants does not lend itself very well to traditional simplification approaches. This thesis presents new algorithms that address these issues at different scales, for rendering individual plants as well as entire landscapes. For individual plants we introduce Displacement Mapped Billboard Clouds, an extended version of the billboard cloud extreme simplification approach. Billboard clouds have been successfully used to reduce the geometric complexity of highly detailedmodels to a few planes, however the resulting models are often unsuitable for viewing at closer distances. The presented extension exploits shaders to improve the visual quality of the resulting models. Also, a method is introduced for quickly determining approximate visible sets for point clouds, which are often used for rendering individual plants. Approximate visible sets allow a significant reduction in the number of primitives to be rendered with only very little impact on visual quality. For entire landscapes, displacement mapping shaders are explored to enhance existing terrain models with vegetation. We also address the issues involved with applying such techniques at a global scale, and present the integration of our method in the open source World Wind geospatial viewer. Furthermore, we propose a way to enable early-Z acceleration methods on the GPU for shaders where this is not yet possible, and discuss the handling of level of detail validity and criteria for time-critical rendering of discrete and continuous levels of detail.