nearphase convex/convex is very slow (cylinders)

[ameent]

Hello there,

I started playing with your library yesterday so my understanding is very limited of it. I'm creating a lot of cylinders (which at the end are just convex polyhedrons). The nearphase algorithm becomes extremely slow and chokes up bringing the fps down to about 10 when I add upwards of 15 cylinders in my scene. When I changed the shapes to spheres, the same amount of shapes cruise along at 60 fps.

I looked into the ContactGenerator class and see that for cylinders the convexConvex function is used which is fairly generic.

I'm thinking that introduction of cylinder as a basic shape may be helpful here. I'll have some time in about 2 weeks and would be more than happy to contribute, however, before I dig my way in a tunnel, I'd like to know a couple of things:

• Is this something you have run into and I'm not aware of a property to set somewhere that would alleviate the issue? (I have tried useBoundingBox = true)
• Are there any docs on what the ContactEquation should hold? The field names are not descriptive, so I'm a bit lost.
• Does introducing a new shape type (cylinder) sound like an idea you're open to?

I'm running the dev branch code.

Thanks! -Ameen

[ameent]

To see the issue I'm running into, change the demos/plie.html and instead of a Sphere in the loop, add a Cylinder as such:

var sphereShape = new CANNON.Cylinder(size/2, size/2, size/10, 8);

[schteppe]

Hello Ameen, I think making the Cylinder into an own type is a very good idea. The convex class is indeed a bit too generic for this case. I'd design the Cylinder like the Box shape is right now: it adds special case code and falls back on the ConvexPolyhedron.

These optimizations could be done, as I see it.

• Special collision cases. For example, making a planeCylinder method for the ContactGenerator is a good and simple start.
• Computation of the AABB & bounding radius and other "virtual" methods in the Shape base class should be implemented directly in the Cylinder class to speed things up more.

Furthermore,

• ConvexPolyhedron should be able to support symmetry axes. This way it could take shortcuts when trying to find a separating axis, for example. However, this requires diving into the ConvexPolyhedron code, which is not the cleanest part of the repo.

Can't think of any direct setting in Cannon, except that .useBoundingBox, that would speed up this.

I agree that the field names (.ni, .ri, .rj) are a not very decriptive. If you can come up with better names, I'd be greatful. Check the source for docs. By the way, .ni, .ri, .rj should be the only fields that you have to worry about.

Please keep using dev branch for development and pull requests.

Thanks for the feedback, and any other future contributions!

Stefan