Interactive Grass Rendering Using Real-Time Tessellation

Grass rendering is needed for many outdoor scenes, but for real-time applications, rendering each blade of grass as geometry has been too expensive so far. This is why grass is most often drawn as a texture mapped onto the ground or grass patches rendered as transparent billboard quads. Recent approaches use geometry for blades that are near the camera and flat geometry for rendering further away. In this paper, we present a technique which is capable of rendering whole grass fields in real time as geometry by exploiting the capabilities of the tessellation shader. Each single blade of grass is rendered as a two-dimensional tessellated quad facing its own random direction. This enables each blade of grass to be influenced by wind and to interact with its environment. In order to adapt the grass field to the current scene, special textures are developed which encode on the one hand the density and height of the grass and on the other hand its look and composition.