High Collision Prims Count

MrRstar

So, I'm just learning UDK and have run into the High Collision Prims note on some of my assets as I import them. I figure this is a problem but can't seem to get the count as low as i think it should be.

I have a tree that i am importing. I've made a collider with 2 cylinders and 4 spheres, all with the gaps between the objects like I've read I should have but when I import, UDK splits up the collider into 40 or so crazy pieces. The collider works as I want it to as I run around the level. But I'm afraid that if I get a bunch of things like this on the level it will bog down. I did find one person saying that he has never had a performance issue with high counts, but I'm not sure I believe that.

mAlkAv!An

Collision meshes need to be convex. If that's no the case, UDK will automatically split up a concave primitive into multiple convex pieces.
http://udn.epicgames.com/Three/FBXStaticMeshPipeline.html#Collision

MrRstar

Ah, yes i knew they needed to be convex. I thought that was talking about the full object though, not the individual quads. I got messing with it today and figured out the differences. However I don't know why it was giving my sphere and cylinder primitives a hard time.

What about my second question? Do collision prims read like geometry or are they handled differently?

Hourences

Its different from normal geometry and I think you are unlikely to ever notice it on a PC, unless you completely overdo it (tons of AI, physics, etc.). For a mobile platform it would be a bad idea.

There is an import flag for when you import staticmeshes by the way, One Convex Hull Per UCX.