View Full Version : stretching skin between joints

01 January 2005, 05:19 PM
I was checking out the elastic foot setup on, a tutorial that many people recommend when it comes to stretching limbs, and I got a little confused. Maybe it's because I am more familiar with max which causes me to think in terms of bones and not joints. It seems to me that the stretching in the elastic foot setup is created by skinning and not the rig itself. let me explain what I mean: if you skin everything to one joint, and stretch your rig, the mesh itself won't be stretched. if we would skin our leg to two joints, only the part that is influenced by both will stretch. this means that if our character was wearing checkerboard pants, he would have square checkers around the hip and foot, heavily stretched out checkers right above and below the knee, and normal stretched out checkers on the knee.

one solution I can think of is to connect the x scaling of my joints to the distance to the next joint:

scaleX = current distance / original distance.

but this creates a pile of work: two locators, a distance and expression for each joint that takes part in the stretching. and when you apply smooth skinning to a 4 joint setup that can stretch only between joint 2 and 3 (thus the scaling of joint2 is changed), you would create unwanted stretching influence between joint 1 and 2.

so my question to you: how would you get an evenly stretching checkerboard pants? :)

01 January 2005, 08:26 PM
the most elegant solution I have come up with is an extra joint for each stretching "bone". for instance, I add another joint parented to the hip, but point constrained to the knee. the vertices halfway my upperleg are skinned to both the hip joint and the extra joint, causing it to stretch, without inheriting rotations from the knee. a lot of extra work during skin weighting, but a fairly easy setup and no unwanted stretching.

I played around with latices a bit, but I can't get it to do what I want. I only want to use the lattice for a linear stretch along the axis of a bone, while the deformations in the joint areas are handles by smooth skinning. I know you can attach a vertex to either the lattice, or the smooth skin, but is there a way to weight it to both?

am I thinking in weird ways? am I seeing problems where there are none? Any input will be greatly apreciated!

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01 January 2006, 08:00 AM
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