Phong Grass: A dynamic LOD approach to grass rendering

Sammanfattning: Background: Recreating nature in a virtual environment comes with many aspects and challenges. Grass rendering is a part of this area, and both performance and visual results must be taken into consideration. A common optimization approach is through static level-of-detail (LOD), however, a certain visual loss comes with the use of this. Dynamic LOD is an alternative technique and exists in various forms, such as phong tessellation. The thesis will investigate the performance and visual implications of utilizing phong tessellation in grass rendering. Objectives: The main objective is to examine the implications of utilizing phong tessellation in grass rendering in terms of performance and visual results. Different scenarios will be examined, providing an overview while identifying performance and visual patterns of the technique. Methods: An experiment conducted via a DirectX 11 implementation was used to collect all data in scenarios that varied in the number of blades and how the tessellation falloff rate was described. The data collected was the average frame time during a 30-second duration as well were rendered images saved to disk from two points of view. Two reference scenes existed that only used a single LOD of either low- or high-quality grass, while no tessellation was applied. The data of each scenario and scene were compared to one another, and the visual differences were identified using the image difference evaluator FLIP. Results: The results show that different scenarios provide different benefits. Some scenarios contain smaller visual errors, while others perform efficiently. Overall a linear detail-falloff rate both performs well at various blade amounts and produces similar or smaller visual differences to the other scenarios. However, the results also show that the technique does not fit every set of hardware, at least not in demanding scenarios. Conclusions: The findings of this thesis show that the method has the potential to be a valid option in terms of performance and visual quality. It is, however, important to consider the specific use case as it is not applicable in every situation and to consider what hardware the application will run on.