Jason Rubin says this on the blog: > Our occlusion worked on a texture level. That is, if we had a giant polygon with a fern texture on it (think many leaves

Jason Rubin says this on the blog: > Our occlusion worked on a texture level. That is, if we had a giant polygon with a fern texture on it (think many leaves but lots of empty space) the occlusion could actually get rid of polygons behind the leaf part of the texture but leave the polygons seen through the alpha channel holes. No other game had that kind of detail in occlusion, and it paid off immensely. Given how small ground polygons could be in the distance, a little fern action went a long way.