Abstract
We propose a novel method for simulating grass swaying with dynamic wind force. Each grass blade is represented as a coarse grass model with four nodes for controlling the grass shape. The control nodes are affected by a physically-plausible wind field which changes the positions of nodes and eventually alters the blade shape with some grass deformation constraints such as stiffness and damping. The wind field is simulated by grid-based fluid dynamics and the grass dynamics is solved by integrating swinging, shape bending and blade twisting. Common grass drooping type can also be handled correctly. For the grass geometry, we first use the coarse grass model to generate a Bezier curve which describes the actual shape of grass. Then, we divide this curve into line segments based on level-of-detail in the tessellation shader and pass it to the geometry shader for grass blade synthesis. By using this simplification technique, we can minimize the grass data needed to be computed and achieve high performance in grass swaying simulation. With 100,000 grass blades and 60X60X20 fluid grid size, our method can run in real time using GPU acceleration.