Real-time Rendering Technology Based On The Dynamic Lighting Of The Large-scale Grass Scene

Modeling and rendering of the natural scenes is an important research area in the field of computer graphics. And grass, as an ubiquitous part of nature scenes, its modeling and rendering technology has been the hotspot for research community for a long time. But due to huge number of grass blades and high complexity of geometry and lighting, real-time grass rendering has been a challenging task.This thesis presents a real-time grass rendering method with high performance and convincing visual effect based on current state of the art research in computer graphics, both domestic and overseas. To provide a growth environment for the grass, this thesis first presents an LOD terrain rendering method based on efficient and crack-proof Quad-tree subdivision. A procedural modeling method base on particle system is adopted to generate geometric models of the grass blades and a three-level LOD grass rendering system is designed based on the geometric models. The three levels are geometry rendering for the nearest distance, volume rendering using both horizontal and vertical slices for the median distance, and volume rendering using only horizontal slices for the farthest distance. The growth of grass on the terrain is implemented by rendering multiple instances of a single grass patch, with random orientations to eliminate periodic patterns. Seamless transition between LOD levels is realized by density control method. For volume rendering, dynamic lighting effects are achieved by using BTFs. For geometry rendering, dynamic shadows are generated by projecting grass blades onto the terrain.The real-time grass rendering system is designed and implemented using OpenGL and GLSL in Visual C++. The system makes extensive use of GPU to meet the real-time requirement and free CPU for other tasks. Results show that our system has achieved high rendering performance and convincing visual effect with good parallax effect.