Improving collisions and self collisions

[josemendez]

Hi, Jose! Thanks for helping me


In fact, my rope isn't stretching and I'm not having any sort of length issue.

I'm talking about flexibility, resistance to bend.

When I increase the resolution parameter (trying to get consistent results during self collisions), my rope becomes flexible (small bending radius).

I need both consistent self-collisions results and low flexibility (large bending radius), though.


You know what I mean? 

Hi!

Yep, now I get it .

The thing with high-res ropes is that they have more particles, and bend constraints only work on 3 particles at a time (they have very low "radius", if you will). So for the anti-bending forces to propagate faster trough the rope, you need to increase the amount of bending constraint iterations in your ObiSolver. Using 20-50 iterations is not unusual for certain scenarios. This is similar to how all constraints work: for them to be more effective at what they do, you need to tell the solver to spend more resources (iterations) on enforcing them.

This will of course impact performance, as more iterations mean more work for the solver. How high you can crank the amount of iterations depends on your performance budget and how stiff you need your rope to appear. Note that getting a perfectly rigid rod using bend constraints would require an infinite amount of iterations. Obi Rope is designed to simulate ropes/chains, which are usually quite flexible by nature.

There's another kind of constraints we will be adding in the future, called "shape-matching" constraints. These would be better suited to keep particles in a certain rigid shape.

You can take a look at this video (excuse my strong accent), which will hopefully shed some more light on the inner workings of bend constraints:
https://www.youtube.com/watch?v=pe5mROQqPv8

cheers!