[ODE] Terrain LOD and trimesh collision detection

[Jon Watte (ODE)]

Jean-Sebastien Guay wrote:

> I was wondering what to do with collision detection in that case. Should I just
> make a trimesh with the highest resolution terrain and let the collision
> detection always use that, or should I update the trimesh with the results of
> LOD every frame / time step?

Most consistent would be to collide with a specific level of detail, 
always. This may or may not be your finest level of detail for graphics 
display. Also note that there is a heightmap collider (I think it's a 
contrib) you might want to look into.

What I would do is cache collision tiles at the right resolution. When 
objects bounding boxes intersect with specific tiles, I make sure those 
tiles are actually in RAM, but if there are tiles that haven't seen use 
for a while, I can re-cycle the memory for those into newer created tiles.

If you have the memory to build all of your terrain at the same time at 
a given level of detail, for collision, then go for it. It'll be faster 
at runtime, and it will be much easier to implement.

> I'm having a hard time figuring out if updating the trimesh often will take
> more time that just using the full resolution terrain in the first place.

The trimesh code has a highly efficient AABB tree built-in, so it's 
unlikely to take a lot of extra time to collide with larger meshes. The 
search time is O(log N) where N is the number of triangles in the mesh.

Cheers,

			/ h+