Animate USD Prims within Maya

[christophezito]

Hello,

I've seen this question has already been asked in this discussion topic.

For setdress purposes or to quickly animate a prop in the stage (Open a door for example), it would be very interresting to be able to animate USD Prims within Maya.

We tried many things to achieve this goal and I wondered if Autodesk or any User have a better approach.

Custom Node

Implementing our custom node that will be placed between two MayaUsdProxyShape nodes, and allow us to interact with the selected Prim to animate it using Maya anim curves, and write time samples on the fly in the USD Stage.

We still have some issues with the LayerManager, as if a MayaUsdProxyShape node has an incoming Stage the incoming node will be in charge of saving the USD edits.

This might not be the better way to do that, as we will have to maintain our custom node as well as a patch of Maya USD to let the leaf MayaUsdProxyShape node be in charge of saving the edits if our custom node is connected as an incoming stage.

Use ProxyAccessor to animate Prims

Using the ProxyAcessor, we can have access to xfomOps and animate the Prims straight into maya setting keys on both side at the same time (Maya keys to the ProxyAccessor's Access Plugs and TimeSamples to the USD Prim)

This Proove Of Concept might work, but we don't have access to Maya Anim curves, and the animation interpolation is linear (which is normal).

Use ProxyAccessor Access Plugs connected to Maya Rig

We tried another alternative: connect all the transform outputs of a Locator to the corresponding ProxyAccessor Access Plug, and an Offset Parent Matrix connection between the Locator and the current Prim's parent (to preserve previous transformation in the graph).
We can bake the Animation, setting Maya keys to the ProxyAccessor Access Plug and adding the corresponding (per frame) Time Samples To the Prim.
This seems to work, and we still need to improve the workflow to retrieve an already animated Prim.

Autodesk point of view

Does Autodesk have plans to make USD Prims animation within Maya?
I guess it would be great to be able to manipulate, animate USD Prims like any other DAG Object, having access to the keyframes on the timeline and in the graph editor, and letting Maya do all the heavy work to write keys on both sides (Maya and USD)

Users point of view

Does anyone else tried to achieve this goal and has a better approach?

Thanks,

Christophe

[kxl-adsk]

The proxy accessor is the foundational piece we were planning to build on top of. I would be curious to learn more about the issues you run into with Use ProxyAccessor to animate Prims. What do you mean by saying that you don't have access to the curves?

[christophezito]

It's good to know that using the ProxyAccessor seems to be the way to animate USD Prims within Maya.

Let me detail the issue we get animating the USD Prims within Maya.
The workflow is as follow:

• Load the stage the usual way using a MayaUsdProxyShape
• Select a Prim, and apply a transformation
• Key the appropriate xformOpon both sides (Maya keyframes and USD Time Samples)

from mayaUsd import lib as mayaUsdLib
import ufe


def keyUfeObject():
    ufeObject = pa.getUfeSelection()
    selDag, selPrim = pa.getDagAndPrimFromUfe(ufeObject)
    stage = mayaUsdLib.GetPrim(selDag).GetStage()
    
    primPath = Sdf.Path(selPrim)
    prim = stage.GetPrimAtPath(primPath)
    
    pa.createXformOps(ufeObject)
    i = cmds.currentTime(query=True)
    for usdAttr in ["xformOp:rotateXYZ", "xformOp:translate"]:
        xformop = prim.GetAttribute(usdAttr)
        pos = xformop.Get()
        """Add a time sample to the xformOp at frame i"""
        xformop.Set(time=i, value=tuple(pos))
        """Add a keyframe to the proxyAccessor plug at frame i"""
        pa.keyframeAccessPlug(ufeObject, usdAttr)

This seems to work as expected, and we can use the "Save USD Edits" callback that will let us choose to save the animation in the Maya Scene or in the USD file.

But there still are some limitations:

• The keyframes are not displayed on the timeline.
• To access the animation curves in the Graph Editor, you need to select the MayaUsdProxyShape, and all the animation curves are displayed (It can be a lot), you can't get only the animation curves of the selected Prim.
• The usual Maya channel box's contextual menu "Set Keyframe" has no effect.
• In order to match the keyframed animation (with tangents) and the time samples, we need to bake the time samples (linear interpolation) at each frame.

These are more limitations from a User point of view. And this actually is the only reason we tried to add a minimal rig on top of the prim to ease the user's experience.

I think the perfect behaviour when animating USD Prims would be:

• To animate USD Prims the same way you animate any DAG Object
• The channel box xformOp available would be keyable
• The Graph Editor would display the selected Prim's animation curves
• The timeline would display the selected Prim's keyframes
• Maya would add the corresponding Prim's time samples (per frame) when saving the USD file
• When reading an USD file with animated Prims (time samples), it would add the corresponding Plug Access keyframes (or interpret them)

But maybe is that what you already have in mind, or even a better approach. Or maybe is that already working out of the box and I miss something in the proper way to animate USD Prims.

We would like to stick as close as possible to the direction you are going to build this feature on, and the simpler might be the better.

[kxl-adsk]

Thank you. The limitations you listed are matching my expectations. We provided a proxy accessor to enable studios to build on top of it, but we don't have yet many workflows that leverage it. The work that currently is landing in dev will take advantage of "parenting" dag nodes under prims...but everything that you listed in regards to animation curves driving prims and the workflows with it is still missing.

I think it's also worth bringing up that some of the workflows you are describing would really benefit from having an official animation curve schema in USD. Yet another big topic for the community to align on.

[bogdanamidzic]

Are there any news on this? It is very very sad how broken whole USD is in Maya. 2 years passed, and it seems nothing changed. We had project which we had to animate inside Houdini, because animating groups in Maya was rocket science. And now 2 years later, opening it and realizing nothing has changed.

In Houdini you can bind USD prims directly to kinefx skeleton, transform pieces, whatever you want. You get these transforms simply written in USD.

[p-hong]

Hello,

We've been looking into migrating our USD pipe to maya2022. Our current maya2020 pipe involves using temporary rig setups created in-shot for USD assemblies. This is to simplify assembly selection, manipulation, and keying for animators. It also lightens up rigging's workload a lot. We also rely on animators being able to set keys on assembly hierarchies as they need, with or without a temporary rig. Transforms can then be baked out at publish.

So it was a big surprise to find out we cannot freely constraint or key USD asset hierarchies in maya2022. Setting keys and constraints through ProxyAccessor might be a good workaround, but is not feasible for shot departments due to the limitations and complexities mentioned above.

Thanks to the insights from @christophezito, we will explore connecting our temporary rigs through access plugs instead of constraints.

Thanks,
Paul

[richardHaw]

any updates?

[wallworm]

Right now there is a proposal from Pixar for animation curves. Our intent is to work on supporting this when official.

[bogdanamidzic]

Are you bothered by the fact that people are waiting for these features for 3+ years?

[wallworm]

Of course we would love to tackle everyone's need as quickly as possible. We would like to accelerate some work here for sure. There are some things we will consider in the coming months around Constraints that can help improve animation workflows. The animation curves directly on USD will add another layer of improvements on animating USD. The truth is that we have several gaps from asset creation to layout to animation to rendering, and we are trying to make significant inroads on all fronts. I can't speak for the past, but I can speak for what we are trying to do now.