Just out of curiosity.
When you guys were developing new character tools for Houdini
(skin deformers in particular) did you concider doing it the same way
“cgCharacter” did it. I mean, like in ACT. Skin deformed by musles.
If you did concider this way of doing it, what made you turn away from
this solution? Is there some serious downflaws to this upproach?

There aren't any purpose-built musle tools right now in Houdini. Are there plans? We haven't seriously approached this part of character rigging yet.

That being said, there have been some fantastic muscle rigs built in the past in both Prisms and Houdini. The tools are there but it is currently up to you to implement your own system. As a brief start, you can parent metaballs to bones then scale with boneangle() using bulge or magnet SOPs. It can get much more complicated and predictable depending on your approach.

I would imagine the biggest advantage to a product like ACT is that they have musle rigs pre-built for you already. This is where the time is spent: Placing muscles inside your character and fine-tuining their effect on the skin.

Now for some history. :wink:

There was Digital Domain and their “HARD” project driven in part by Caleb Howard and Academy Award Winner Kevin Mack way back in 1994 using PRISMS!
David Oliver also pioneered a muscle system with help from some R&D for the Disney Dinosaur project. From what I understand, David was able to acomplish with Prisms what took quite some time of hard development with what would become maya and they still didn't capture all of what was in the original Prisms solution.
Most recently, Primal Pictures developed their own muscle system tools for Houdini that are probably more accurate than those in ACT. Very clever those Primal guys. Many more muscle projects inbetween of varying complexity.

The bulge SOP actually came out of C.O.R.E.'s custom tool for doing muscle simulations.

Thanks for the input old_school.

That being said, there have been some fantastic muscle rigs built in the past in both Prisms and Houdini. The tools are there but it is currently up to you to implement your own system. As a brief start, you can parent metaballs to bones then scale with boneangle() using bulge or magnet SOPs. It can get much more complicated and predictable depending on your approach.

Now, this is something for me to to loose sleep over it and twist my brain.

I tried to write a Vex SOP to formulate the NURBS CVs to Deforms the Vertexs Polymesh in my model where the NURBS are the muscles and bones and the PolyMesh is the skin. I tried to use blend regions and tried to figure out how to pipe the point SOP as the input to average the regions between the NURBS and the PolyMesh but so far I have not been successful. Any Suggestions? If you want I will post my Vex SOP as a Jpeg so you can see my setup. Maybe I am just going about it all wrong. I don't know.

Cheers,
Nate Nesler

Please post the Vex SOP snapshot.

As for the NURBs cv affecting vertecies in a polymesh, what function(s) are you using to accomplish this? It could be difficult and slow in VEX or just not possible right now.

Wouldn't it be very CPU intensive to deform a mesh with metaballs?
The metaball count most sertanly will go very high.
I guess my question is, how hard are the metaballs for Houdini to compute? Will high number of metaballs noticeballly decrease performance?

An ACT type of muscle system combined with the current rigging system that Houdini comes with? That would be a very good thing.

By the way. Would it be possible to get metaballs to push each other away instead of merging together?
I can imagine that this could be done in POPs but, as I said, what I'm looking for is not “push away force” for animating metaballs, but simply for shaping them. Squishing, if you will, each other at the point where two forces overlap.

Never mind my last question.
I just got it answered at OdForce.
If anyone interested,Here is the link [odforce.net]

If I could pipe in both the point groups to the blend region perhaps I would be successful. I am not really sure though. Thanks for all your help!!

Cheers,
Nate Nesler

P.S. Just out of curiosity how much would you be willing to pay for an ACT type system on Houdini?