I am new to Houdini, so please bear with me.

I am trying to test a muscle setup using vellum fiber constraint. As per the docs, the muscle fibre direction vector should be initialized on v@materialW, which I have done.

What are the steps we need to do to make sure that vector is being calculated in the simulation space?
Should I use a SOP solver to update the materialW each frame? Any inputs on this is much appreciated.

I just figured this happens automatically. Yay

Hi Seemag,

Do you know anyway to apply the materialW direction per point and controlling it using line of action? Similar to what ziva's zfiber constraint does?

Thanks

Hey sorry for the late reply,

You can attach external SOP into the vellumsolver, and use those values to multiply the stiffness in the vellumConstraintProperty.

So you can build a line of action network outside and copy the length values to each of the muscles and attach that to the vellum solver as an external SOP. I dont have an example to share, but i tried it and it works.

Also , You dont need to do anything to direction of the materialW, you can just set it however you want in the beginning before feeding it to the solver. Houdini will keep that direction relative to the geometry through out the simulation(that was my initial question and after testing I found that it actually works).

So you just need to set the the stiffness of the constraint (for flex) using the lineOfAction setup.(using an external SOP)

I am trying to contract a vellum tet mesh using an animated materialW attribute.

I have created the attribute in a point wrangle upstream to start off as {0,0,0} so the tet doesn't contract

how can I animate the y value of that vector using a float channel attribute in a SOP/point wrangle and the
the vellum constraint properties node would update every frame to that value?