Static Meshes: Collision Primitives VS Blocking Volumes - Performance

[DyotoOrion]

Hi Unit23! Yes you can create your own custom collision objects in any 3D software (Well, i know it works for Blender 3D, Max and Maya and probably Modo). Yes, I personally use Blender 3D for all my game assets.

Making custom collision inside Blender 3D is really easy. I’ll explain it briefly in a moment. But first here’s an example of one of the Static Mesh environment objects for my game, for which a custom collision object is pretty mush essential, just to show why I am using this method:

Here you can see the base Static Mesh (5200 Tris):

And then the Collision Asset (1100 Tris):

As you can see the “Concave” nature of the asset means that an auto generated collision would be useless and using Blocking Volumes would just be a mega pain in the ***.

So yeah to export custom collision asset from Blender -> UE4. Make your low poly collision asset in Blender as a separate object (It must have no holes in the mesh - IE all contiguous geometry, otherwise it can yield bad results in UE4.). Your collision object must be named UCX_ObjectName and must have the exact same Object Name as your Static Mesh, but with UCX_ at the start. Select both your objects and export as FBX. Check “Selection Only” in the export options. Import to UE4 - in the Static Mesh Import options uncheck “Auto Generate Collision” and uncheck “One Convex Hull Per UCX” (That option simplifies collision assets to single collision primitives) and click import. Voila! When you open your Static Mesh in the Static Mesh editor, click the “Collision” button to view collision and you should see your collision as a purple wireframe mesh!

So to answer your last question Unit 23. You cannot have “1 Sided” collision assets / primitives. If you try to make a single sided collision asset, UE4 will create an incorrect primitive that goes off into infinity. Try it you’ll see what I mean. Also that’s why you can’t have “holes” in your collision asset - the collision mesh must be watertight and it must have some volume. The most simple custom collision mesh you can create is a Tetrahedron (3 sided pyramid), and as far as I can tell more complex collision assets are broken down by UE4 into multiple tetrahedrons (the most simple collision primitive).

Thanks for your answers guys - hope you found this all interesting.

@unit23;632621

I wasn’t even aware that you can import your own collisions, do you use blender or something else? I am not sure if i would need something like that. However, when you merge meshes, for instance floor tiles, the generated collision is always a cube shape, and then you can align the heights. If you would create collision yourself, you probably also want to use cube forms, instead of many different angles, or spheres ofc. Though, for floors and walls you would just need single sided collision, and i am currently not sure if you can delete the other side which is normally automatically created. Just some thoughts