Polytope to TriMesh

Game Mechanics
#1

hi

I am trying to use the collision data from Quake3 BSP maps. This data is stored as so called brushes, which are actually polytopes (defined by a set of planes). Since common physics engines only know trimeshes, I would like to convert these polytopes to trimeshes. But I can’t find any good coding examples for this.

A dumb solution would be to compute all cutting lines between the planes, sort out the relevant ones and compute the cutting points between them and finally create the desired triangles from these points. Of course this is not very smart and will be quite expensive. I suspect, there’s a smarter way.

Could anyone point me to good examples or give me other hints?

Thanks in advance.

Marvin

#2

I haven’t used quake3 maps before, but do the BSP’s come in a tree structure? You could use this to know which planes to intersect. I haven’t thought about that much, but then you might get away with only having to test intersections directly between a parent plane and it’s children.

#3

JBullet supports them directly as ConvexHullShape. It uses point cloud, to which you can convert by using GeometryUtil.getVerticesFromPlaneEquations.

The advantage is that it has actual volume, which is better for discrete collision detection (less chance of missing than with triangles).

#4

Yes, the brushes are in the BSP tree as well as the map’s geometry. Maybe it is worth more to risk doing the collision detection manually (if the used physics engine doesn’t support convex hulls), since the BSP tree will do a lot more for performance. I will try it.

Thanks a lot.

Marvin