Summary

Title:Cloth collision problems
Category:Workflow
Status:Open
Posted By:Gregg ( Gregory Glezakos )
Date Created:16 September 2015

Problem

Description:

I'm not sure if this is ment to be this way or not, but...

If i sim two simple plane objects as cloth falling on one another and both on a box object and also having the "show particles" active, i get rather good collision detection between them.

With the same resollution and settings, if i don't have the "show particles" active, the collision is gone and the two planes don't see each other. At least, not as they did before; if there is collision there, it's not working as it should.

On the same topic, if i do simulate with the "show particles" active and turn that off after the simulation, then the cloth meshes look more like broken fluids rather than cloth objects...

So, are these user errors like something we shouldn't be doing or something weird going on here?

I'm using the today's latest Lucid version...

Cheers,
Greg

Steps to Reproduce:

Create two plane objects with 200 segments on both axis and a sphere with 32 segments .

Place them all at the 0,0,0 origin.

Move the first plane in Z axis above the sphere.

Move the second plane in Z axis above the first plane.

Make the sphere a Collision object.

Make the two planes a Cloth object.

Add the Lucid settings in thr scene and set the res to 200.

Activate the "show particles" in both plane objects.

Record the simulation for 100 frames.

Notice the "proper" collisions.

De-activate the "show particles" in both plane objects.

Notice the "broken" look of the plane (cloth) objects.

Once more, record the simulation for 100 frames.

Notice, the collisions we had before are gone and the two planes are interpenetrate each other.

I forgot to mention, that i was using 50 sub-steps and 10 iterations, when doing these tests, along with a 200 resolution...

 

BTW...

Using lower resolution like 60, we get better collision between the cloth objects but the expense of needed detail. the gap between the collisions is too obvious then...

Thank you for a detailed description Greg, I will have to go over these steps and see what I can discover. There should not be any difference in collision behavior if you use particle or mesh display so that is most likely some bug.

Marsel Khadiyev (Software Developer, EPHERE Inc.)

Okay...

Scratch everything i said about the collisions between the cloth objects; they seem to work now even with higher resolutions.
I could swear they didn't work before, but sim upon sim, they work now...

Anyway, the only thing that doesn't seem to work is the "show as particles" activated befeore the simulation and deactivated right after the simulation; keeps ruining the cloth objects...

I'll post a video soon...

Alright...

Here's a video with the latest finds:

https://vimeo.com/139532602

Since i'm showing some problematic behavior, i wasn't sure if i should go public with it, so i put a password: lucid

Greg

Looks good Greg even despite the errors :)

I can now see what you mean by using "Display as Particles" first and then turning them off. What happens is that the particles are meshes as if they were a fluid rather than recombining them into cloth mesh as it should happen. This is a bug which I will fix.

Regadring interpenetration, it looks like the mesh density is pretty high so it could be particle tunneling. Please try to increase sub-step count to see if that is the case. Higher sub-steps will help fight any tunneling problems.

Marsel Khadiyev (Software Developer, EPHERE Inc.)

So, i removed the error/bug portion of the sequence and made the video available to public view...

https://vimeo.com/139532602

Feel free to repost... :)

I'm not sure how to do it myself on FB... :)

Thank you Greg, just posted it on our social channels. Did you try to add more sub-steps in the sim?

Marsel Khadiyev (Software Developer, EPHERE Inc.)

Uhm, not yet unfortunatelly...

I'll get more tests soon tho...

Sounds good!

Marsel Khadiyev (Software Developer, EPHERE Inc.)

Siming right now!
With 200 sub-steps and 20 iterations i get ZERO penetrations, super tight collisions and much better looking cloth folds!

I'll render a video this time and post soon the results!

Even in preview they look gorgeous! :)

Soooo....
Any hint about when we should be getting those "lock vertices" or "pins"?
Really can't wait to try cloths on characters!

We're working on particles right now but I will spend some time over the weekend to see if I can get the ball rolling on this. Great to hear that substeps are improving the results!

Marsel Khadiyev (Software Developer, EPHERE Inc.)

Hi Marsel...

Here are the rendered results...

https://vimeo.com/139778582

Cheers,

Greg

 

Wow, that is quite an improvement. Thank you, I posted this up on FB.

Marsel Khadiyev (Software Developer, EPHERE Inc.)

Greg, we have tried to reproduce this scene here locally without much success (there was twisting involved). Would it be possible to share the scene from the last render for us to study?

Marsel Khadiyev (Software Developer, EPHERE Inc.)

Sure thing...
It's pretty consistent here every time i sim it...  


Attached Files:

>Lucid005.rar (68506 bytes),

Awesome, thanks a bunch.

Marsel Khadiyev (Software Developer, EPHERE Inc.)