Saturday, March 29, 2014

Tip: Using timeline animation for Set Driven Keys on rig deformation


I was trying to deform an elbow area of a character i'm rigging and i wanted to maintain a sharp elbow and not have the biceps collapse.  So this time around i tried creating a locator for the inner elbow and a locator for the outer elbow (added these as influences to skin and assigned some rough weights to the areas i wanted the locators to effect).

The interesting thing i tried now was to set normal animation key frames on the locators  and a key frame at the elbow joint (for appropriate rotate axis and rounding value) even before i assigned appropriate weighting to the influences.   I then edited the weighting of the locators to get an improved look on the corner of elbow and at inner bicep.   By scrolling through the animation timeline i could get an idea for when i want to begin changing deformation (moving the influence locators).

Then i wrote a kind of pseudo code for the animation values in preparation for set driven keys later and placed it on something i could easily look at and save in Maya.  I used a nurbs curves name.

Here is an example:
(basically the "first curve's" name is saying when the elbow joint is at rotation in z of -164 the corner locator skin influence should be at a translation in x  of 0.35 and a translation in y of -0.08.
Here's an idea for a before and after (using locator influences .. the after has a couple topology changes to help improve deformation)

Finally i used these values in a set driven key on the elbow to improve on its deformation.

One reason i used this set driven key behavior as opposed to corrective shape is because i'm still working on the topology of the character.  Changing topology using correctives would require me to resculpt corrective, but changing topology using driven keys on skin influence i can still use Maya's copy skin weight tool to put weights onto new topology.  In the future when topology finalized probably corrective would be a more elegant solution.

Hope this is helpful,

Inspired by
Alex Alvarez's "Skinning 4: Smooth Skin Influence Objects" (alexalvarez dot com)
Carlo Sansonetti's "The Skinned Character Rig: Skinning and Deformations" (carlosansonetti dot com)