What makes a rig "ephemeral?"

When there's danger in Node Graph City, the NGPD shines a node callback into the sky. As if from nowhere, Ephemeral Rig Man appears! When his work is done he vanishes...into the night!

Last time we talked about the problems caused by keyframe interpolation, and the benefits you can get by removing it altogether. But because we can't use Source Filmmaker for production--it's really not geared towards character animation--we're going to need to figure out how to get some of those benefits in Maya.

Some of those benefits are easy to get. Maya was designed for a series of separate animation curves for each attribute, with it's own keyframe placement and interpolation. But we don't need to think of them that way--we can make a "pose," with a keyframe on every attribute associated with the character, and choose to animate only with poses. "Breakdown" tools like Justin Barrett's The Tween Machine or our own Anzovin Breakdown Tool can be used to generate in-between poses easily. Indeed, this is a well-established workflow for blocking, even when the final animation will be splined and adjusted through the graph editor.

Some benefits are harder to get. Working with poses effectively really requires you to be able to see other poses while you are working, which is best done through some sort of onion skin tool in the manner of a 2D DCC app like Toon Boom. Maya is really not designed to do this, but there are a number of possible solutions--I'll go over onion skinning in a future post.

And some benefits seem, at first blush, impossible. In theory, a truly pose-based system would let you completely change the rig's behavior between poses. But even if you're thinking of your motion in poses, Maya isn't. It still thinks you have a bunch of animation curves driving a bunch of attributes that must remain consistent to allow for interpolation--actually changing the rig in an arbitrary way would completely destroy your motion. Maya is built to think about rigs as pre-defined little machines, and that's the opposite of what we want.

So we need a concept of "ephemeral" rigging--rig behavior that does not use the node graph! To Maya, ephemeral rigging is essentially invisible. It's triggered by some callback or manipulator, performs some rig behavior on the scene, and then vanishes, as mysteriously as it had appeared!

Here's the two initial tests I've put out for the ephemeral rig system I'm currently working on:

Note that the control rig has no keyframes, allowing you to arbitrarily change the rig. The "attach" command I'm using here just parents the control to whatever you want. That includes being able to completely reverse the hierarchy if desired, or parent controls to something external to the character. No special consideration is needed for "space switching," because the controls have no canonical space to begin with!

Using this system, you could decide you want the hand to be parented to the head. After adjusting the pose, you scrub over to another pose. When you do so, the hand is still parented to the head, but both the hand and the head controls have conformed themselves to the pose you've scrubbed over to. This allows you to configure the rig in any way you want without disturbing any pose, and then use that configuration to manipulate any pose you choose.

There are a number of ways to implement this. What I'm doing here uses API node callbacks that fire when the control rig is manipulated. When they do, they get the world transformation matrix of the control rig node being manipulated and use it to figure out what values the geometry rig needs to receive to match its pose. Since I am starting with the node's world-space matrix, hierarchy is entirely irrelevant.

When I've had a few more posts to lay down other aspects of my overall workflow, I'm going to circle back to ephemeral rigs and go into detail on how this system works, with code samples.