Chain multiple MayaUsdProxyShape nodes sharing Stage

[christophezito]

Hello,

We are trying to implement a custom loadStage node that simply loads the Stage, nothing more, and propagate it through the DG.
The goal here is that we would like to:

• Load a USD Stage
• Add a custom node in between and do some stuff
• Display the USD Stage

But we are stuck by the LayerManager, that (as far as we understand) does not handle other node types than MayaUsdProxyShape nodes.
Patching maya-usd for our purpose might not be the best option, and using a MayaUsdProxyshape in place of our "custom" loadStage node would be better.

So we wondered if it was good practice to chain two or more MayaUsdProxyShape Nodes, and if there was an extra cost using such a rig (see the example below).

Thanks

Christophe

world_scene.usda

#usda 1.0
(
    defaultPrim = "mayaUsdProxy1"
    endTimeCode = 96
    framesPerSecond = 24
    metersPerUnit = 0.01
    startTimeCode = 1
    timeCodesPerSecond = 24
    upAxis = "Z"
)

def Xform "world"
{
}

import maya.cmds as cmds


stage = "world_scene.usda"
layer = "Kitchen_set/assets/Chair/Chair.usd"

""" load plugins """
plugins = ["mayaUsdPlugin"]
for plugin in plugins:
    if not cmds.pluginInfo(plugin, query=True, loaded=True):
        cmds.loadPlugin(plugin)


""" MayaUsdProxyShape to load Stage """
proxy_shape = cmds.createNode("mayaUsdProxyShape", name="loadStageProxyShape")
cmds.setAttr(proxy_shape + ".filePath", stage, type="string")
proxy_transform = cmds.rename(cmds.listRelatives(proxy_shape, parent=True)[0], "loadStageProxy")
cmds.setAttr(proxy_shape + ".visibility", False)
cmds.setAttr(proxy_shape + ".lodVisibility", False)
cmds.setAttr(proxy_shape + ".hiddenInOutliner", True)
cmds.setAttr(proxy_transform + ".visibility", False)
cmds.setAttr(proxy_transform + ".lodVisibility", False)
cmds.setAttr(proxy_transform + ".hiddenInOutliner", True)
cmds.outlinerEditor(refresh=True)

""" MayaUsdProxyShape to display Stage """
display_shape = cmds.createNode("mayaUsdProxyShape", name="displayStageProxyShape")
cmds.connectAttr(proxy_shape + ".outStageData", display_shape + ".inStageData")
display_transform = cmds.rename(cmds.listRelatives(display_shape, parent=True)[0], "displayStageProxy")

""" Connect time information """
time = cmds.ls(typ="time")[0]
cmds.connectAttr(time + ".outTime", proxy_shape + ".time")
cmds.connectAttr(time + ".outTime", display_shape + ".time")

""" Add layer """
root_layer = "|" + proxy_transform + "|" + proxy_shape
cmds.mayaUsdEditTarget(root_layer,
    edit=True,
    editTarget=stage)

cmds.mayaUsdLayerEditor(stage,
    edit=True,
    insertSubPath=(0, layer))

[kxl-adsk]

Yes, you can absolutely chain proxy shapes, but you have to be careful to make sure the right shape receives changes. I see you did it above...just one FYI. You can use intermediateObject attribute to prevent one proxy shape from drawing.

Additionally, you have to keep in mind that stage is shared across src and dst nodes...so whatever will be edited upstream, will as well be edited at the source. This gets pretty messy is you start branching to multiple dst nodes and create a graph of dependencies (instead of chain). We created an unshared composition mode (attr on the proxy shape) in which the proxy shape will put the incoming stage layer stack under a new root layer.

Having a dedicated node isn't a bad idea either since the proxy shape has a few more features you don't care about. It's unclear to me if you really need to make it supported by LayerManager? Do you want to allow downstream to mutate the upstream state?

Cheers,
KxL

[christophezito]

Hello,
Thank you for your valuable reply @kxl-adsk .
I wasn't aware of this intermediateObject attribute which is really a better way to use a MayaUsdProxyShape as a "stage loader" only.

Thank you for sharing this advice.

Custom load stage node

As for implementing a custom node which purpose would be to only load a stage and propagate it to the inStageDataAttr plug of the MayaUsdProxyShape, I made the assumption that as the LayerManager only handles MayaUsdProxyShape or MayaUsdProxyShapeBase node types, we needed to patch it to add our loadStage node to the supportedNodeTypes.
But It might be too intrusive and would change too much the LayerManager's behavior.

As far as I understand, if a MayaUsdProxyShape has an incoming stage, the LayerManager will let the first MayaUsdProxyShape node being responsible of saving the edits.
So we tryed another approach overriding the fact that if a MayaUsdProxyShape has an incoming stage and if this stage comes from our custom node it would use THIS MayaUsdProxyShape to be responsible for saving. It partially works for now, as the edits are properly saved, but we still have an issue that we will fix when reloading the Maya Scene.

Thanks again for your reply,

Christophe