The GPU Based Rendering And Dynamic Simulation Of Vegetation Complex Scene

Complex vegetation scene is an important element of outdoor scenes. It often occupies most of the users' vision in the three-dimensional scene. The photorealistic and real-time interactivity of complex vegetation scene will directly affect the users' immersion in the scene. However, the construction of this kind of scene is very complicated. In addition to the terrain, the scene also contains a large area of grassland and a wide variety of trees. In order to meet the users' requirements of the photorealistic and real-time interactivity of complex vegetation scene. This thesis, using the latest GPU-based programmable rendering pipeline technology, researches on the realistic rendering and dynamic simulation of grass and photorealistic rendering of trees, as well as the implementation of the complex vegetation scene rendering system.First, to solve huge amount of data transmission and low rendering efficiency when drawing the meadow scene, this thesis applies tessellation and geometry shaders to draw massive grass. When rendering grass scene, CPU only needs to transfer a small amount of mesh data to GPU, then, tessellation function is used to produce a large number of vertices. According to the vertex coordinates generated by tessellation stage, the geometry shader can draw grass in GPU which is a good solution to handle the CPU and GPU data transfer bottlenecks. Using tessellation factor can well control grid subdivision level which makes it possible to adjust the grass density according to position of the viewpoint. Benefiting from the geometry shader, dynamic simulation of grass can also be done on the GPU so that the CPU no longer affected by the heavy computing tasks, significantly improved the performance of the rendering system.Second, in terms of rendering mass trees in vegetation complex scene, this thesis uses a hardware-based instancing technology. In the drawing process, this method can effectively reduce the amount of data transmission between the CPU and GPU, and decrease CPU interference during the drawing process, which enhances the rendering efficiency. In terms of realistic rendering of trees, this thesis replaces traditional lighting model by physics-based lighting model to render tree leaves. Based on positional relationship between viewpoint and the light source, lighting calculations are performed on both sides of the leaves so that leaves could have more realistic appearance. For trees trunk in the scene, this thesis takes advantage of the latest tessellation technology to render the trunk with a concavity. Depending on the viewpoint position, it is possible to control the levels of trunk's subdivision, achieving a smooth transition between different trunk details.Finally, data, logic and rendering are separated from each other in order to improve the rendering efficiency in the rendering system. The fog effects and surface details are added to make the vegetation complex scene more realistic.