View Full Version : ClothFX trouble

Mr. Limpet
01-28-2011, 04:59 PM
Using ClothFX for the first time and having an issue.

I am doing a product shot. The top has a round lid structure like a canning jar but instead of a solid center it has a stretchy fabric like nylon stockings.

When the lid goes on, the content in the jar slightly protrude through the top of the lid, pushing out and stretching the fabric.

I got the whole thing put together using a disc object for the fabric, a point selection around the rim of the disc to "fix" the fabric into place, ClothFX applied to the fabric and collision applied to the protruding object.

Basically it all works. But I am getting tearing on the fabric.
Tried many settings of Spring, up to 5000 and down to 50. No change.
Tried Stretch limit up to 200, No help.
Took Polygon size up but that merely broke the surface up badly.
Tried Thin Cotton, Thick Cotton, Silk, Rubber. No solution yet.

Any ideas?

Mr. Limpet
01-28-2011, 05:21 PM
I considered that.
The protruding object sometimes moves around under the fabric,
so the stretching fabric would have to animate as though something under it was also moving across the underside of the fabric in addition to pushing it out.

Gary Heck
01-28-2011, 05:27 PM
I'm not sure this could be the problem. Is the geometry subdivision set to last?

Mr. Limpet
01-28-2011, 06:15 PM
Hi Gary,
Went to the geometry tab in the object properties panel and switched subdivision order to last. Ran the calculation again and nothing changed. Fabric still tears along the edge of the area where the protruding object stretches the mesh. Also tried increasing the sub structure numbers but that didn't help.

Going to try changing settings in the collision tab under dynamics and see what happens.

01-28-2011, 07:01 PM
Do you have a scene I could look at?

Mr. Limpet
02-07-2011, 04:10 PM
I started this thread a week ago and then got drawn into other graphics last week. So I am back again at trying to solve this.

I am posting two clips illustrating the problem.

I played with all the controls in ClothFX.
The only one that seemed to make a difference was the "Collision Offset" setting under the Collision tab.

The clip where the fabric does not tear has the Collision Offset set at 140.
That seems to be about the threshold below which the cloth tears as in the second clip.

But, setting Collision Offset this high produces very long calculation times.
So, to investigate adjustments to all the other ClothFX settings, I set the Collision Offset lower and experimented with everything else. But nothing seemed to have any effect at all. As if there is something I need to enable to get the functions to work.

I suspect the pinching effect on parts of the stretched cloth is caused by the underlying mesh. The mesh was created as a simple square and then with 30X30 polys and then cut with a stencil into a circle. The polys were then tripled for finer detail.

The online manual is pretty much worthless for this. It has a section which discusses each setting but vaguely say things like "setting this function high does X and setting it low does Y". Not giving any idea what settings would be considered "low and high".

I purchased and downloaded a tutorial from Kurv last night and will go through it tonight. But most of the tutorials that I have found online are such simple things like "making a flag" or draping a square of cloth over a ball. These kinds of things don't push the settings at all and are kind of worthless.

This should get a more thorough explanation in the manual.

I will review the Kurv material and in the meantime perhaps someone, like Dodgy, who may have used ClothFX before will have some ideas.

The simple solution in the ClothFX settings would seem to be the "stretch limit" under the Advanced tab. But it seems to have no effect on the problem.

OK, thanks in advance for any ideas.

02-08-2011, 05:10 AM
Is the fabric object a subpatch object?

If not then try tipple-ing the polygons, part of the problem may simply be non-planer polys so if you tripple them thats sorted.

The other problem is parts of the underlying objects poking through; I forgot the setting name but you can change how far away from the surface the objects need to be before a collision is registered. That settings needs increasing to the point where the objects no longer pass through.

If the object isn't a subpatch object then obviously, changing the Subdivision Order, will do nothing.

02-08-2011, 05:20 AM
I think posting the scene files would help a lot more... it's tough describing stuff when it's causing problems... it could be anything at all! :D

02-08-2011, 06:19 AM
As lardbros says, giving me a scene file would probably help the most as I have no ideas what your settings are.
My first guess would be that the mesh, despite being fairly finely subdivided, isn't subdivided sufficiently at the area where the tearing occurs.

Collision occurs between points on your clothfx mesh and polys on the collision object.

Consider 2 adjacent points in the cloth object. If they each hit adjacent polys adjoined by a sharp enough corner, the edge between them will pass through the edge adjoining the polygons in the collision mesh. The collision offset counteracts this by trying to collide the points further away from the collision polys, hopefully stopping their adjoining edge interpenetrating.

This setting is highly dependent on the density of your cloth object. Too high and points will be continually trying to calculate collision with your object, too low and your object will pass through. It's not a save all setting, as you do need a dense enough mesh to work well.

Mr. Limpet
02-08-2011, 11:18 AM
OK guys, thanks.
I will finish the Kurv tutorial, see if I can learn anything and then repost including the project.

Skonk, the cloth object is not a subpatch object so I will look at that as well.