Physics objects overlapping when jointed


I’ve been using jointed physics objects in the past, but never noticed this: when I create physics polygons and then connect them with a distance joint, the object are attracted towards each other (which is normal), but then overlap as if contacts didn’t apply anymore. I’m not sure if I’m clear, so I’ve done this video.

Any idea what could cause this problem?

@Rodolphe Anytime I have physics objects overlapping is when the physics object rotates but the visual image doesn’t rotate properly to match it so the visual images overlap.

Thanks Dave. It doesn’t seem like this is my issue, but it’s a good point. I’m investigating… :slight_smile:

@Rodolphe this is normal, if you create a weld/rope/distance/slider etc the two bodies of that joint will stop colliding. I like this behaviour, but it would be nice to be able to make them collide. Because of this I’m using a ROPE joint with a length of math.huge to make objects not collide, so if this behaviour were to be fixed then it’s best if it’s optional to collide the two bodies.

@Rodolphe I think @Luatee is correct. I have a rope that I created with a lot of physics.body(Circle) linked together with joints. I can move the rope around in loops and make it overlap with itself. If the collision was in effect, then it wouldn’t overlap.

Alright, that makes sense now! Joint objects not colliding with each other is quite problematic for what I’m trying to achieve though… Any advice on how to get around this would be appreciated! cheers!

@Rodolphe I wonder if there’s a way to link none jointed objects to your jointed ones. That way, the none jointed objects will collide and stop the overlaps. But I’m not sure if that’s possible.

That could work, but I’m trying to keep computation at a minimum, my ipad I struggling to compute the scene as it is right now

@Rodolphe @dave1707 is probably right in his suggestion, I’d suggest you create two instances of the body, say a and b. Weld a to b, set b.sensor = true and that should work. If mass is an issue try to set b.mass = 0, that probably won’t work with the joint though.

Edit: Or axis a very small body to the center and use that as a body for the joint.

Thanks Luatee, trying your Edit piece right now.

Your suggestions worked, thanks a lot!!!

That’s very well done @Rodolphe and exactly what I meant. Your game is coming along nicely :slight_smile: But I still think this issue should be sorted out with an optional collide parameter with the joint, not sure if @Simeon or @John want to have a say in the matter.

Thanks! oh yes, I think we definitely need an option. this method works but it increases the number of joints and bodies by quite a lot (and we often need as much ressources as possible, I know I do)

Well if I were to do this in my game I’d only be allowed to have around 50 props with joints whereas now (on iPad Air) without having collision I can get up to 100 and still be on 60fps. I’m grasping at every single bit of memory I can get hands on, but some things aren’t avoidable unlike this with such a big advantage.