A very advanced method to do grass rendering with dynamic lightning. There are shadows cast from each grass straw and you can paint a density map to select where you want grass and how much. The grass is obviously also animated in a very realistic way. The following is how they describe the technique briefly.
“We use a combination of geometry and lit volume slices, composed of Bidirectional Texture Functions (BTFs). BTFs, generated using a fast pre-computation step, provide an accurate, per pixel lighting of the grass.”
Link to more images and the paper: