Monday, August 13, 2012

Got 99 Problem and a ...

So I was asked by someone about the problems and the short comings of the Maya smooth-skinning.
It is times like this, that I realize how little I know about rigging...and after some research and asking "real" riggers about it, these are what I came up with...

Problem of smooth skinning:
When using linear-blend/smooth skinning the main issues is the
limitation of geometry deformation, smooth skinning in (Maya)
manipulates vertices using a
weighted average of transformations.

All possible positions that the vertexes
can travel to lies between the influences. The problem is that a set
of vertexes can't be weight painted to achieve shapes that doesn't
fall within the subspace determined by the influences.

In common situations such as shoulders and
elbows the desired deformation does not lie in this subspace, hence
no amount of adjusting the algorithm weights will produce good results.

Normally I will have funny pic to show here but ... DO NOT...Google Image..."skinning" at work

1. corrective blend Shape:
If the production does grant the use of (Maya) blend shapes, using
tools such as "B Spirit", allows the rigger to
sculpt out corrective blend shapes that can be apply before the smooth
skinning layer in deformation.

Using joints within the rig to drive
the weight of the corrective blend shape. By using both a blend shape
and smooth skinning it gives the most control on the final
look of the geometry, giving the best result artistically.

2. helper joints:
Creating a system of joints that are driven by control joints, working
with the base skinning joints.
The helper joints convert the motion of the control joints in
ways that aid the skinning process (a bicep helper joint for example might
convert the elbow rotation to a translation).

The helper joints are skin to the
same skin cluster as the base skinning joints but gets moved to help
the smooth skinning joints to create a desired shape when control
joints are posed. Similar to how the corrective blend shape is driven
but without the use of blend shapes.

Here is a link to my Rig Demo that shows how I solve the problems describe above

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