[UE4] - Collision Hull (Using Planes)?

EliasWick

Greetings!

Can you use a plane for collision in UE4 or does it have to be a box or something that is "intact"?
For example: If I am making a floor which is just a plane. Do I have to add a box for a collision, or can I just use a plane?

Kyetja

You can just use a plane! You can just make you collision in i.e. Maya or 3DS Max and export it to UE4.
https://www.youtube.com/watch?v=uXGW6Vf2rzY

EliasWick

Kyetja said:

You can just use a plane! You can just make you collision in i.e. Maya or 3DS Max and export it to UE4.
https://www.youtube.com/watch?v=uXGW6Vf2rzY

Hey Kyetja... Thanks for the answer... I've spent 12 hours reading through forums and came to the conclusion that you can't use a plane for a Collision Hull. The mesh has to be enclosed, in other words be a box... It' can't be a single polygon.
Can you confirm any of this?

Obscura

Yes they should be closed shapes if you want to do it with primitives.

EliasWick

EliasWick said:

Kyetja said:

You can just use a plane! You can just make you collision in i.e. Maya or 3DS Max and export it to UE4.
https://www.youtube.com/watch?v=uXGW6Vf2rzY

Hey Kyetja... Thanks for the answer... I've spent 12 hours reading through forums and came to the conclusion that you can't use a plane for a Collision Hull. The mesh has to be enclosed, in other words be a box... It' can't be a single polygon.
Can you confirm any of this?

Edit: I spent some more time looking and found an answer... You can't use a plane for Collision in UE4. So what you said "You can just use a plane!" is incorrect.

See source below:

UCX_[RenderMeshName]_##

Convex objects can be any completely closed convex 3D shape. For example, a box can also be a convex object. The diagram below illustrates what is

EliasWick

Obscura said:

Yes they should be closed shapes if you want to do it with primitives.

Thank you for the clarification! I notices that UE4 transforms my plane collision to a box collision when using UCX
By the way, I love the new profile image!

Obscura

lol. 

Actually you could have a plane kind of collision setup if you would really want to. I think the per poly collision can act like 2 sided, so what you could do is to import a plane, make it colliding per poly, and attach it to your mesh. But I dont see a point of doing this.

Kyetja

See source below:

UCX_[RenderMeshName]_##

Convex objects can be any completely closed convex 3D shape. For example, a box can also be a convex object. The diagram below illustrates what is

But can't you set the collision type to simple? I recall doing something like this before, my bad if I remember that incorrectly hehe, maybe you can search on that.

jlazzaro

I have a floor in my current project that is a simple plane made of 2 triangles. To setup collision, I went into the static mesh editor and choose "add box simplified collision."

EliasWick would be looking for. No need for making a custom collision mesh (assuming we're actually talking about a plane and not some complex flat mesh.

EliasWick

Kyetja said:

See source below:

UCX_[RenderMeshName]_##

Convex objects can be any completely closed convex 3D shape. For example, a box can also be a convex object. The diagram below illustrates what is

But can't you set the collision type to simple? I recall doing something like this before, my bad if I remember that incorrectly hehe, maybe you can search on that.

Hey, that's true. That is what I did for my models.

Setting		Description
Default		This will cause simple collision requests to use simple collision, and complex requests to use complex collision; the "default" behavior.
UseSimpleAsComplex		This means that if a complex query is requested, the engine will still query against simple shapes; basically ignoring the trimesh. This helps save memory since we don't need to bake the trimesh and can improve performance if the collision geometry is simpler.
UseComplexAsSimple		This means that if a simple query is requested, the engine will query against complex shapes; basically ignoring the simple collision. This allows us to use the trimesh for the physics simulation collision. Note that if you are using UseComplexAsSimple you cannot simulate the object, but you can use it to collide with other simulated (simple) objects.

EliasWick

jlazzaro said:

I have a floor in my current project that is a simple plane made of 2 triangles. To setup collision, I went into the static mesh editor and choose "add box simplified collision."

EliasWick would be looking for. No need for making a custom collision mesh (assuming we're actually talking about a plane and not some complex flat mesh.

Thank you! I found this a bit later after I asked the question. Still... I would really want to know if there was a way to create a custom collision with only planes, but that seems to not work.

jlazzaro

As far as I can tell, when doing the box simplified collision, it appears to be functionally equivalent in size to a plane. So my guess is that it's making a box with a height that's 0 units (which is basically a two sided plane).  So perhaps you could experiment in your 3d modeling package with either two sided planes, or boxes that have a height of zero?

EliasWick

jlazzaro said:

As far as I can tell, when doing the box simplified collision, it appears to be functionally equivalent in size to a plane. So my guess is that it's making a box with a height that's 0 units (which is basically a two sided plane).  So perhaps you could experiment in your 3d modeling package with either two sided planes, or boxes that have a height of zero?

Thanks, the idea of a box with 0 in height should work, technically speaking. Thanks again for all the help!

Butthair

Best habit for collision is to use water tight meshes, basic primitives and meshes with some thickness are ideal.

UCX is the standard I believe, no more UBX or USP or MCDCX suffixes like UDK days.

For a ground floor, which is just a plane, a box is sitll ideal. Furthermore, if you begin to make stories for a buildings, lets say, then your floor becomes a ceiling also. It's better to think about your collision as the volume that this mesh takes up, meaning thickness.