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To quote the docs

Normally cloth uses the state of the object in the first frame to compute the natural rest shape of the cloth, and keeps that constant throughout the simulation.

Is it possible to specify this "natural rest shape" explicitly?

My use case is the following: I'd like to simulate "tightening" shoelaces to have them follow a natural position without manually modelling all the collisions. Initial results are promising.

I've loosely modeled the path of the shoelace using a curve and curve modifier:

enter image description here

I hook the ends of the lace to an empty and move that using keyframes. After simulation I get a result which is close to what I want, however there are some weird twists where the shoelace previously went through the eyelets.

enter image description here

It seems like the simplest solution to this problem would be if it were possible to specify the base, straight, shoelace as the "natural shape" of the mesh. However, I'm not seeing any obvious appropriate option... am I missing something or is there some workaround?

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  • $\begingroup$ And yes, I looped the the back middle eyelet the wrong way around - sorry about that :-) $\endgroup$ Commented Jan 17, 2023 at 23:55
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    $\begingroup$ Maybe straighten the curve on frame 1, set pinning to 1.0 for all verts on frames 1 and 2, maybe via vertex weight edit modifier, and then let it run? Not sure if there's a way to set explicit rest shape, but you can define the rest shape from frame 1 and then override on frame 2. $\endgroup$
    – Nathan
    Commented Jan 18, 2023 at 0:20
  • $\begingroup$ just set the beziercurve to minimum instead of z-up - i think that's getting closer to what you want $\endgroup$
    – Chris
    Commented Jan 18, 2023 at 6:21

2 Answers 2

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setting beziercurve to minimum gives this result:

enter image description here

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OK, well, it turns out the exact option I was expecting does actually already exist.

https://docs.blender.org/manual/en/3.4/physics/cloth/settings/shape.html

Rest Shape Key

Allows starting the cloth simulation using a specific shape key as the rest state, instead of the shape that results from evaluating shape keys and preceding modifiers in the regular way. This option is mutually exclusive with Dynamic Mesh.

This can be used to start the simulation with the cloth in a pre-draped state without applying that shape as a plastic deformation that relaxes all springs as a side effect.

The reason I didn't find it is that it only shows up if the selected object already has shape keys.

enter image description here

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