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I'm working on an animated scene with quite complex cloth simulation (2.83-2.90). Multiple characters and layers of clothing. The dress in the foreground is working perfectly now after much error and lots of trial. But I'd like to find a way to add more inertia/mass to the lower hem of vertices somehow, to give a sense of weight to the fringing along the bottom (this is created with particle hair btw).

I haven't tried stiffness scaling, as I don't want to change the stiffness of the cloth as such afaik. I thought about subdividing that part of the mesh, but this would likely mess up all the collsion/self-collision. Any thoughts anyone? Or do I just need to hope vertex group control is added someday? ;)

EDIT: I just discovered that this feature was implemented in 2006 Blender but later simplified/removed. Still wondering if there's a way to cheat this somehow.

from On what Cloth Simulation Model is Blender Cloth Physics Based? re: 2006 Blender:

Mass Scale Vertex Group : This vertex group allows the user to multiply the point mass by the influence/weight a vertice has in the vertex group. Thus parts of the cloth can have different weights making part of it appear wet or heavier for other reasons.

Mass Vertex Group : This vertex group allows the user to directly specify the weight of the vertices. The Scale parameter is used to adjust the results of this.

Scale : This allows the user to scale the results of applying a Mass Vertex Group.

Cloth simulation with fringed hem

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    $\begingroup$ i beleive weight painting is what your looking for $\endgroup$
    – TheRealist1969
    Commented Jun 12, 2020 at 11:54
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    $\begingroup$ I know it might sound like that, all this talk of mass and weight, but I'm referring to the mass of the physical simulation itself, which isn't controllable with vertex weights as far as I am aware. $\endgroup$
    – Stephen Hamacek
    Commented Jun 12, 2020 at 12:26
  • $\begingroup$ Did you try the Physical Properties: Vertex Mass? While it should be the place where you can control the real weight that is considered, it also fast totally changes the behavior, as one would suspect. If the cloth simulation is cached and the particle fringing simulated based on that, i believe fine tuning the mass could help. BUT you won't get the cloth like self collision with the particle system. Rather i would suggest to consider making a separate cloth fringing, in case you want the realism (it sure looks that way). $\endgroup$
    – Xylvier
    Commented Jun 12, 2020 at 12:38
  • $\begingroup$ I've tweaked most parameters many times, and have a vertex mass that works well for this silky cloth overall. But is if there is a way of adding to the mass just on the lower part of the mesh? The fringing is hair dynamics attached to the cloth, and it behaves very well but it doesn't interact with the cloth simulation, only after following the cloth position. Is there a way of attaching another cloth simulation to the bottom of the dress and have them both simulate together and interact? I'm not sure if that's possible, but if it were that could give that variation in mass I'm looking for. $\endgroup$
    – Stephen Hamacek
    Commented Jun 12, 2020 at 13:59
  • $\begingroup$ I've edited now to clarify that this is for animation btw. $\endgroup$
    – Stephen Hamacek
    Commented Jun 12, 2020 at 14:17

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Ive spoken briefly with some devs who suggested this feature could be added to the cloth sim again in future. In the meantime, I did manage to create a cheat that works well enough in this case:

  1. Added additional geometry at or near the bottom of the hem. In this case more or less a dense bunch of 10 loops within a couple of centimetres;
  2. Assign these additional verts to a vertex group, and excluded them from self-collision, and;
  3. assigned them a new transparent shader so they don't show in renders.

This made a distinct difference and got basically the result I wanted. Still hoping for a more elegant solution via the devs though, as there are multiple cases where vertex weighting mass would have application.

Hard to post animated visual results yet, but feel free to keep an eye on @LMODanimation or thelovemeordie.com if you want to see more soon.

Thanks for looking!

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