Add a cylinder mesh to bevy_render

[allsey87]

What problem does this solve or what need does it fill?

Cylinders are a fundamental shape and we should have a means of generating cylinder meshes in Bevy. Currently the closest option to this is a capsule shape.

What solution would you like?

The addition of a Cylinder shape and implementation of From<Cylinder> for Mesh.

What alternative(s) have you considered?

• Modify the capsule so that the ends could have zero radius?
• Import a GLTF

Additional context

PR #305 implemented this feature but was closed before merge. I would like to bring this PR back to life and get it merged, however, meshes, normals, UVs etc are not my area of expertise and I am having some problems with the UVs/normals I think (see below). Perhaps I can open a new PR for this? Some more commits will be necessary to get the rendering working.

[alice-i-cecile]

Have you seen the geometric primitives RFC? :)
bevyengine/rfcs#12

It's ready for community comment, so your input on this topic would be valuable.

[Rust-Ninja-Sabi]

Is it now possible to make cylinder from the standard shapes?

[alice-i-cecile]

This should be constructable via the Capsule type.

However we should at the least add a helper method for this.

[JayPavlina]

I attempted this, but I don't think it's possible to create a cylinder from a capsule.

• radius controls both the radius of the capsule section and the radius of the spheres on the ends. Setting radius to 0 makes it invisible.
• rings does not have any noticeable effect
• depth changes the distance between the spheres.
• latitudes and longitudes just change the resolution.

Also I experimented with RegularPolygon, and it could be used to create the caps, but not sure how to create the column connecting them.

I think a cylinder needs to be a separate shape.

[alice-i-cecile]

Sounds good, I'd be happy to have this implemented as a seperate shape.

[JayPavlina]

I'll take a look at #305 and see if I can revive it, but I'll probably have the same problems that @allsey87 had with UVs/normals. But I'll see how it goes.

[rparrett]

I'd be happy to donate the cylinder code here: https://github.com/rparrett/typey_birb/blob/main/src/cylinder.rs

I had intended to PR it at some point but I'd be happy if someone else did that work.

[JayPavlina]

@rparrett Feel free to do the PR then. I don't know how to fix the lighting on the other one, but I put yours in the 3d_shapes example and it looks perfect.

Edit: Oh I just saw that you said you'd be happy for someone else to do it. I can do it then.

[rparrett]

Yeah, feel free to PR that code if you want. Maybe add the author of #305 and me as co-authors if you want. IIRC, my code was very loosely based on that one (docs still seem pretty similar) but I abandoned most of it when the UVs weren't behaving and referenced... some old textbook somewhere.

I don't need another PR on my plate at this moment though.