Game Development Reference
F IGURE 12.3
Bottom-up hierarchy building in action.
namic worlds where objects are constantly in motion (a space shooter, for example),
the hierarchy needs to be rebuilt during the game.
I will give an overview and flavor of how hierarchies can be constructed, but it
would take many chapters to go into complete detail. You can find more information
in Ericson .
The following are the three approaches to building a BVH.
Bottom-up The bottom-up approach (illustrated in figure 12.3) starts with a
list of bounding volumes corresponding to individual objects. Pairs of objects
are chosen based on the requirements of the hierarchy just discussed, and a
parent node is added for the pair. This parent node then replaces the objects
in the list. The process continues until there is only one node left in the list.
To p - d o w n The top-down approach (illustrated in figure 12.4) starts with the
same list as before. At each iteration of the algorithm the objects in the list
are separated into two groups so that members of each group are clustered