Bug / Crash Obi adding huge forces to rigidbodies when you delete ropes... (Repro project)

[josemendez]

Well, it sounds like the only supported solution to have every rope collide with one another is to have the entire game parented to a ObiSolver GameObject?

Having every rope collide with every other rope does require to have all your ropes under the same solver.  However that's not usually what you want, unless everything in your game is made of ropes and can potentially move to anywhere else in the world.

And to write our own Object.Instantiate() method that parents everything we instantiate to that object, in case it contains a rope?

That's literally 2 lines of code, doesn't seem like much of a drawback to me.

It'd be very difficult to work with PhysX if it had those kinds of inflexibilities.

Actually PhysX works *exactly* the same way: you need to include Actors in a Scene for them to be simulated. Actors in different Scenes do not interact with each other. From their docs:

https://docs.nvidia.com/gameworks/conten...ction.html

The basic concepts of the world within a PhysX simulation are easy to visualize:
- The PhysX world comprises a collection of Scenes, each containing objects called Actors;
- Each Scene defines its own reference frame encompassing all of space and time;
- Actors in different Scenes do not interact with each other;

Unity creates a single Scene for you under the hood and puts all physics objects inside it for you. This actually gets in the way sometimes and has been a huge source of frustration for many people (including me) over the years. You didn't have explicit control over scenes or a way to have more than one physics scene until recently, and even now it's done in a quite clunky way:

https://learn.unity.com/tutorial/multi-scene-physics

This is the same architectural pattern used by Flex, Bullet, ODE, Box2D, Havok, and all other physics engines I've ever used or heard of. It's is not an inflexibility imho, but quite the opposite: it allows you to explicitly partition your world into independent simulations, allows you to perform local-space simulation (which is an absolute must for large game worlds) and it does so in a way consistent with how Unity works.