just to note: Collision Detection can be maintained without rendering if objects are set to Alpha 0.
Thanks, but I knew that already :) Are they meshes or sprites?
meshes, about 50 polygons
can you texture them with less surfaces?
I guess they have 2 surfaces, the trunk (solid) and the leaves (transparant)... I tried grouping them in less meshes with addmesh(), add them to a mesh based on their location, but the 3D engine doesn't support zbuffer on transparant surfaces (or something like that, someone from blitz support explained it to me but I don't have the mail right here), which caused trees to pop up in front of eachother. And it didn't really increased the FPS by much.
can you replace meshes with sprites at greater distances (L.O.D stuff)?
My camera is top-down (well, tilted a bit, but from the top), which means you can't look very far anyway. There are typically 10 trees on screeen at once, and they are not far enough away to replace them with a sprite.
But I'm pretty sure most of the slow-down was caused by the engine checking the collision between my players and every single tree that was in the scene. Now it only has to check a few trees, and it's a LOT faster.
Thanks for the suggestions.