wierd collision behaviour

I have imported some pretty simple meshes I use for rooms and set these to use complex collision which works fine when there is only 1 material on the mesh

If i select some wall polygons in UE4 and assign a different material to a new material slot, then these polygons then are excluded from the complex collision and my character walks right through this wall

What gives?

Complex collision is a really bad idea for anything at all. Why not just add a collision box to your model and utilize simple collision?
especially on something simple like a wall…

because they block doors and stairways etc, and besides I these are minimal poly meshes that I optimised for complex collisions

I found a workaround…I can duplicate the mesh in UE4 and add it as a complex collision mesh before texturing the original mesh, but I think it sucks that adding a material removes those polys from the complex collision detection…unless im doing something wrong as a noob?

You can use mesh LODs for collision:…ion/index.html
And you can create LODs with Python or BP scripts:…ODs/index.html

Using LODs for collision is the best way for any object that doesn’t have a quite simple shape. That is if you need player characters or any AI driven NPC interact with it or if you want any collision to look realistic.

I just ran into something similar in case you’re still working on it.

I had an object that somehow at some point in time the material on the object was turned to ‘no collision’. (in the model file- not in bp or material file.)

The assertion that simple collisions don’t work with doors is simply ridiculous.

Create 3 boxes of collision and you get reliable simple collision on a door at a cent of the performance complex provides.

The assertion simple collision doesn’t work with stairs is equally insane, but complex vs UCX/UBX and simple might not offer much savings if you need every step to have collision.

The LOD idea is great too, but you would probably still have more LOD detail then a UBX component.

Study up if you haven’t.