Ephemeral Rig Mark 2


Last time, I talked about some of the issues I had with the existing ephemeral rig system, and that I planned to rebuild it. I didn’t talk about how I planned to rebuild it in any detail, because if I did there was a chance I was going to make a complete fool of myself. Luckily, that’s not what happened, so now you get to hear about how I’m writing my own rigging system, with it’s own dependency graph and it’s own constraints, that only connects to the Maya scene graph at specific points. And how this was actually much easier than it sounds.

First of all, take a gander at this:

Of particular note is the paired hand and prop controls. The old system would have allowed you to attach the hand to the prop, or the prop to the hand, but it would not have allowed the seemingly two-way connection you see here. I say seemingly because there isn’t actually any cycle-breaking going on here. What’s happening is that the dependency graph that exists when you select the hand--representing all the rigging behavior in the control rig, including hierarchy--, and the graph that exists when you select the prop, are two entirely different graphs. I simply have it rebuild itself from scratch any time anything changes. It will rebuild if you look at it wrong. It will rebuild if you sneeze. But it builds so fast--16 milliseconds for this three-control rig--that you’d never notice. This means that instead of hacking around with reparenting or constraining controls in Maya, I can just have the graph remake itself to work however it needs to work at this particular moment.

This diagram may make the behavior more clear:


Conceptually, this is very similar to how the old system behaved: there’s a deformation rig that has keyframes, and a control rig that does not and is only used to manipulate the deformation rig. Previously, however, while the connection between the control rig and deformation rig was ephemeral, the control rig still existed in Maya as Maya transforms being evaluated through the Maya DAG and DG, each with it’s own callback to pass it’s data onto the deformation rig ephemerally.

Now there’s only one callback. It pulls data only from the node the user is currently manipulating, and all other rig behavior is evaluated by the ephemeral DG’s own nodes, with no connection at all to Maya’s evaluation. Then it pushes it’s data back to the Maya scene. And that’s the only other place it touches the Maya DG at all. It’s fast, too--evaluating this three-control rig takes a little less then a single millisecond, despite running a node graph that was written in Python, not exactly a language known for its performance.

This solves a huge number of problems. Remember all the hackery I had to engage in to get the ephemeral rig behavior to work when the control nodes were in Maya? Well I don’t have to do that anymore. No more special attribute to tell you whether or not you are on the current pose. Now I just kill the graph the moment the playhead leaves the current frame, and create it again the moment it stops. I mean, imagine deleting nodes and connections in Maya while in the process of scrubbing! But with my own nodes and DG, I can have them do whatever I want.

Similarly, the old system presented endless problems with undo. Because changing modes meant actually changing the Maya scene graph, getting it back into the right configuration to undo any given change was becoming a nightmare. While I don’t have undo fully working yet for the new system--you may notice that’s one thing I don’t do in the video!--tests suggest it will be far easier to implement for this system, since the graph has no persistent configuration in the first place, and there is no longer any concept of a “matchback” from the deformation rig to the control rig that would have to be triggered correctly.

I’ll be going through more details about how this system works in the next few posts.