Skinned cloth simulation clipping

[josemendez]

Hi, I'm working on an Obi Skinned Cloth shirt on an animated character, with an ambient force zone around them that changes direction. Depending on the arm position and the direction of the wind, sometimes there is some clipping between the sleeves and the side of the shirt, where the wind blows the cloth under the armpit outwards, leading it to clip with the sleeves of the shirt when the character's arms are lowered. These screenshots are from my initial cloth blueprints:
https://gyazo.com/58704254eb5c6f29a9e61df98ef49c97

To be fair, some of this is because of the original mesh design, here is a screenshot of the mesh with no cloth simulation:
https://gyazo.com/2d6b14283956874ca3b4c80a751c55f7

I've had some success with increasing the mass, skin radius and backstop of the particles directly underneath the arm, which looks good when the wind is blowing towards that side of the shirt, but when the wind is in the opposite direction, the increased skin radius results in even more clipping
(wind blowing left) https://gyazo.com/24ca161db1378b6acdbd465465729193
(wind blowing right) https://gyazo.com/b70b20e0b74cc11a1f0c7dae6c1f3ee9

Any advice for what kind of parameters would allow the particles to sink into the mesh (when the wind is blowing towards that side), but restricts the particles from moving away from the mesh surface?

Hi there!

Skin constraints impose two "off-limits" zones for a particle:

• outside the sphere defined by the vertex skinned position and the skin radius value
  
• inside the sphere defined by the vertex skinned position/normal and the skin backstop radius/skin backstop values.
  

The first one is pretty intuitive (i'd like to think) as it's basically a "don't move too far away from the skinned position" constraint.

The second one creates a "virtual" spherical collider behind the particle at each vertex (lets call it the "backstop" sphere), so that the vertex can't get too far back inside the character's body. The catch here is that the center of the backstop sphere is placed along the surface normal, at a distance of backstop radius (the sphere's radius) + backstop (the distance from the surface). So if your mesh has pre-modeled wrinkles/folds in it, the backstop spheres will be in weird positions (to the left or the right of the surface, because that's where the cloth normal is pointing), instead of right underneath the cloth surface which is where you want them. Am I making sense?

The solution would be to model your cloth with as few wrinkles as possible (the simulation will add result in wrinkles anyway), making sure that all normals point away from the body as much as you can.