Here’s an idea for a new constraint that I think might prove handy.
http://www.sonic.net/raillard/hash/spherical_translate_limits_constraint.gif
Currently we have a Translate Limits constraint that allows a bone to rattle around inside a box, defined by three maximum and three minimum parameters, in the X,Y, & Z planes, respectfully.
This new constraint would be similar, except it would keep the constrained bone within a ball. My picture shows how it might work. I show what would happen with three possible settings.
In the first case, the minimum diameter setting is set to 0 and the maximum diameter setting is set to 6 cm. This would allow the constrained bone to be translated anywhere inside a 6 cm. diameter sphere.
In the second case, the minimum diamter setting is set to 4 cm. and the maximum diameter setting is set to 6cm. This would allow the constrained bone to rattle around between two spheres. It can go no closer to the origin than 4 cm, and it cannot go beyond 6cm.
In the third case the minimum diameter setting and the maximum diameter setting are both set to 6 cm. This would force the constrained bone to stick to the surface of a 6 cm. sphere.
I don’t know how difficult it would be to program such a constraint, dumb artist that I am. Still, I’m fairly certain it would be very useful. Consider the Setup Machine rig. Currently, the SM rig uses a plain old Translate Limits on the Bicep control bone. The underlying shoulder geometry bone (which is hidden) has an Aim At constraint, which points to the Bicep control bone … hence, you can control two bones, the bicep geometry bone and the shoulder geometry bone, with this one control bone. This is sweet. Why hassle with two bones if you can use just one? Well, actually there is a reason why you might not like this. Since the bicep control bone is free to bounce around inside a box, it no longer perfectly superimposes the underlying bicep geometry bone, whose origin has to move in a sphere defined by the length of the shoulder bone. This is not really a major deal … but it does produce a bit of wiggy behavior within the automatic elbow pointing rig, from time to time. To the best of my understanding, this is the chief reason why the Setup Machine offers the option to NOT install an automatic elbow control system. However, it cannot be denied that an automatic elbow managment system is a nice thing to have! Anyway, this is my chief gripe against the SM way of shrugging shoulders, and why I prefer a visible shoulder bone. If this new spherical translate limits constraint were available to us, then the SM way of doing things would instantly become the preferable alternative for everyone. A visible shoulder bone would become a thing of the past.
Okay. I’ve made my case. Feel free to throw flowers or bricks at it.
Respectfully,
Carl Raillard