I'm trying to animate the "Rest Length Scale" of the Pressure Constraint that is connnected to a Cloth constraint.

Unfortunately enough one can't animate constraint values directly so I figured I can use a "Vellumconstraintproperty" in the DOPnet to do that.

But that only gives access to the "Rest Length Scale" of the Cloth Constraint , which is resulting in something completely different then animating the "Rest Length Scale" of the Pressure Constraint.

Is there a way to animate the "Rest Length Scale" of the Pressure Constraint without having to take a course in Vex ?

Thanks.

You don't really need a course. It's only two lines of VEX code. Check out this post.
https://www.sidefx.com/forum/topic/87419/ [www.sidefx.com]

Hey thanks.

I checked the scene. Looks great, but as far as I get it, it's just a fancy way to animate the rest length of the Cloth Constraint with a Vellum Constraint Property and a gradient mask ( restlength = mask; ) ?

But what I'm looking for is access to the Rest Length Scale of the Pressure Constraint that is connected to the Cloth Constraint in this particular setup...

When you override an attribute for animation, I believe all of those attributes are the same. The Rest Scale Length for a Cloth constraint is the same as the Rest Scale Length of the Pressure constraint.

Try this line of VEX code with the Rest Length Scale box enabled.

toonafish
But what I'm looking for is access to the Rest Length Scale of the Pressure Constraint that is connected to the Cloth Constraint in this particular setup...

those constraints are independent of each other and Vellum Constraint Property can work on all constraints so it's just matter of defining the correct constraint group

you can also have a look at AnimatedPressure example file in help, which while not completely correct in terms of volume computation, it may provide a good starting point

Great, thanks a lot for the pointers, I'll give it a try.

Thanks for pointing that out, Tomas. After specifying a new group name, pressure_stretch, the constraint vellum properties node can isolate only those for processing.

Strangely enough the "animated pressure constraints" scene from the Help, completely freezes up Houdini as soon as I hit "play".

I can fix it by replacing the "rubbertoy" with a simple torus, then the dynamics work as expected.

But as soon as I edit the Torus, like adding an edgebevel or duplicating it, the scene freezes up again when I try to play and run the simulation.

Is it me, or is this a bug ?

Houdini 19.5.493 / Nvidia RTX 4090 / driver version 528.49

To answer my own question, setting the OpenCL device to CPU in the preferences solved the freezing issue. ( Preferences -> Miscellaneous )

Probably another Nvidia driver issue.

Just in case someone else runs into the same problem.