ROA算法的优化

s. We can use a more tricky data structure of our patches than just a simple grid - a quadtree. This will allow us to do quick and effective occlusion. Do not forget that when checking whether a quad is in or out of the frustum, that the nodes are not simply 2D squares but also have a third component - height. Cylinders can be reused, as they have already been prepared for an "up" orientated check.