Rendering Grass in Real Time with Dynamic Light Sources

Since grass is very abundant on the Earth's surface, it is an important element of natural 3D scenes. Real-time realistic rendering of grass has always been difficult due to the huge number of grass blades. Overcoming this geometric complexity usually requires many coarse approximations to provide interactive frame rates. However, the performance comes at the cost of poor lighting quality and lack of detail of the grass. In this report, we describe a grass rendering technique that allows better lighting and parallax effect while maintaining real-time performance. We use a novel combination of geometry and lit volume slices, composed of Bidirectional Texture Functions ({BTF}s). {BTF}s, generated using a fast pre-computation step, provide an accurate, per pixel lighting of the grass. Our implementation allows the rendering of a football field, covered by approximately $627$ million virtual grass blades, with dynamic lighting, shadows and anti-aliasing in real-time. The creation of arbitrary shaped patches of grass is made possible using our density management