Hi guys, I'm having some trouble using bone length for squash and stretch as it's giving me crazy deformations that I cant fix. (see attached file) if anyone knows how I can solve this, it would be much appreciated. Also, the other problem is, how would I do volume preservation with the stretching? In maya we'd use the joint scales but scaling bones in houdini seems to be bad idea. Any help would be much appreciated. Thanks

Hi Patrick,

for volume preservation, what you're looking for is the crscale parms on the bone.

For the nasty deformations you're getting - that is just a bit of a hitch with how bones are created by default inside Houdini…

Right now, when a bone is created it's length parm is referenced by the zfactor parm on the cregion inside the bone. This causes multiple problems, but the one you're seeing is due to the fact that not *all* of the cregion is being scaled when the length changed - only the middle (tubular) portion. The end caps on the cregion remain constant in scale, which is why you see horrible stepping in your mesh when you adjust the bone length.

The answer I've found that works best is to break the channel reference to the cregion zfactor and instead drive the crscalez parm (labelled “Deform Region Scales”) on the bone itself by dividing the “length” by the “captposelen”.The crscalez will stretch the cregion as a whole (endcaps included) and give you the nice smooth deformation that you'd be expecting.

The funny thing is, that if you look inside the Bone object and find the cregion, you'll find in the Region->Animate tab a parm called “Squash and Stretch”… which is driven by the bones “Deform Region Scales”… which kind of makes sense of it all

Anyway, that was lengthy… here's a hip file!

thank you @friedasparagus this is great. Thanks much.