02-10-2023, 07:33 PM
(31-08-2023, 07:56 AM)josemendez Wrote: Yes, all units are per-particle. Changing resolution and width will affect density (mass per volume/length unit). The reason for this is that you're typically more interested in the mass ratio between a single particle and another object than the mass ratio of the entire rope vs another object.
On a side note, a mass ratio of 1:720 will break pretty much any physics engine (except for direct/reduced coordinates solvers). Always try to keep mass ratios below 1:10.
I just tried a similar setup and couldn't reproduce any issues with 12 substeps, 1 iteration and a 1:5 mass ratio. Would it be possible for you to send your setup to support(at)virtualmethodstudio.com so that I can take a closer look?
Obi uses speculative contacts for CCD. It sweeps bounding boxes (of both particles and rigidbodies) by their velocity, and then generates a contact constraint between their closest points. Velocities and positions of both are then constrained so that the contact planes don't cross each other.
Yes, this is how it works. However a particle can only get past/inside the SDF if all previous contact detect&solve attempts have failed or if another constraint has forced it inside the SDF after contact constraints have been solved, both situations are very rare.
SDF collision detection in Obi is based on the following article, FYI:
https://mmacklin.com/sdfcontact.pdf
Nope, Obi predicts rigidbody position/orientation and uses this information during CCD checks. Rigidbodies shouldn't be able to go trough stationary ropes even if it's speed is large compared to rope thickness.
Note however that CCD isn't perfect. In particular, collision detection is performed only once per step (see: http://mmacklin.com/smallsteps.pdf). If a particle is pushed trough an object during a constraint solve, there's no way to prevent this (only solution would be to perform full collision detection/resolution after every single constraint iteration, which is of course impractical).
kind regards
To give this thread some closure I had figured out what was going on. I had a spring that only affected forces one-way, and the damping factor was causing the rope collision resolution to be less effective. Making it two-way fixed the problems. I can now thread a rope through the box, grab it, and use it as a makeshift zipline like intended.
Crossing two ropes so they look like two interlocking V shapes and shortening them still causes tunnelling, but I imagine that's just a consequence of the lengths becoming lower than that configuration can handle. I can with live that though.
Thank you for your help