USD Stage Editor Quick Start

Unreal Engine provides support for USD through the USD Stage Actor and the USD Stage workflow. In this Quick Start guide, you will:

• Creating the USD Stage Actor.
• Editing properties using the USD Stage Window.
• Adding new Prims to your USD Stage Actor.
• Writing data back to your USD file.
• Accessing USD animations using Sequencer.
• Importing assets into an Unreal Engine project.

Before you begin, you will need the USD Importer plugin enabled in your project. For more information, see Working with Plugins.

Prerequisite Topics

In order to understand and use the content on this page, make sure you are familiar with the following topic:

• Universal Scene Description in Unreal Engine

This tutorial uses the Kitchen Set USD file from Pixar. Pixar maintains a small library of USD sample files for learning and demonstration. Download the Kitchen Set and other samples here.

1. Creating the USD Stage Actor

Start working with USD content by opening the USD Stage panel.

Click image for full size.

1. In the Level Editor, from the Top Menu, select Window > Virtual Production > USD Stage.

2. From the menu in the USD Stage Editor panel, select File > Open and navigate to your USD file.

The Hierarchy section will populate with the scene hierarchy from your USD file.

The Hierarchy section of the USD Stage window populated with the contents of the Kitchen Set. Click image for full size.

Each USD file you open in Unreal Engine requires its own USD Stage Actor that serves as an anchor for your USD data. The process outlined above will automatically add a USD Stage Actor to your Level.

It is also possible to add a USD Stage Actor using the Place Actors panel and select an associated USD file for it using the Root Layer option in the Details panel.

2. Editing Properties Using the USD Stage Window

You can edit the properties of your USD Stage Actor and prims using the Properties section of the USD Stage Editor window.

Changing the UpAxis of the USD Stage Actor

1. Select Stage at the top of the hierarchy in the USD Stage window. In the Properties section, locate the upAxis property and click the dropdown menu. Select the new axis to represent up for your USD data.

   Select the axis the best fits your USD data. Click image for full size.

Changing the Variant of a Prim

1. In the USD Stage Editor, select Options > Selection and enable Synchronize with Editor. This synchronizes your selection between the Unreal Engine Level and the USD Stage Editor window.

   Enable Synchronize with Editor to synchronize your selection between the USD Stage and the Unreal Engine viewport. Click image for full size.

2. In the Hierarchy section, click the dropdown arrow next to Kitchen_Set to expand the group. Expand Props_grp to display the props in the scene.

3. Expand West_grp to display individual prims. Props highlighted in orange indicate that they are composition arcs, and you can right-click any of their prims to add references to them (or clear references from them). Other right-click actions include the ability to add or remove prims, and the ability to toggle, load, or unload payloads.

   Click image for full size.

4. Expand DiningTable_grp and select ChairB_1. In the Properties section you can edit the following:

   Property	Description
   name	Displays the name of the selected asset.
   path	Displays the path of the selected asset.
   kind	Defines the type of the selected asset. assembly: Collection of models. component: Type of model that contains subcomponents. group: Collection of models within an assembly. model: Base type of kind. Assets should not have their kind set to model since it is an abstract commonality used to differentiate components and groups. For more information, see Model Hierarchy in the Pixar USD documentation. subcomponent: Prims inside a component. Not a type of model.
   purpose	Sets the initial Purpose to load. Uses a USD Stage Actor and an integer as input. Options include: default proxy render guide
   visibility	Sets the initial Purpose to load. Uses a USD Stage Actor and an integer as input. Options include: inherited: Inherits visibility from its parent invisibile: Prim and any prims included in its subtree are not rendered.
   xformOp:rotateZ	Defines the Z rotation of the selected asset.
   xformOp:translate	Defines the X, Y, and Z location of the asset.
   xformOpOrder	Displays the order in which transform operations are applied to the asset.
   modelingVariant	Defines the current variant being displayed in the scene. It will only be visible if the asset has one or more variants.
   References	Displays all references attached to this prim.

5. The chairs in this scene have two variants, ChairA and ChairB. With ChairB_1 selected, locate the Variants section of the Properties. Change modelingVariant to ChairA. This will swap the chair mesh used in the scene with the new variant.

3. Adding New Prims to Your USD Stage Actor

Prims are added or removed from the hierarchy using the right-click menu. Once added, their properties can be edited in the Properties section.

Adding a new chair to the Kitchen Set

1. Right-click the DiningTable_grp entry in the hierarchy and select Add Prim from the menu. Name this new prim ChairB_3.

   Adding a new prim to the USD Stage. Click image for full size.

2. Select your new prim in the hierarchy. In the Details section, change its kind to component.

   Changing the properties of the new prim. Click image for full size.

3. Reference the chair USD file to bring it into the stage. Right-click ChairB_3 in the hierarchy and select Add Reference. Navigate to the location of your Kitchen Set files. Open the assets > Chair folder and select Chair.usd. Click Open.

4. Your new prim now references the Chair USD data and displays the ChairA variant. It should be located at the Level's origin. Select ChairB_3 in the hierarchy and change the modelingVariant to ChairB.

5. Click the new chair in the viewport and use the transform tools to place the chair near the table.

4. Writing Data Back to Your USD File

Changes made using the USD Stage Actor can be written back to your USD file. From the USD Stage panel, select File > Save.

5. Accessing USD Animations Using Sequencer

Accessing USD Animations

Animations stored within a USD file are accessible from a specifically-generated Level Sequence spawned by the USD Stage Actor.

1. In the Outliner, select UsdStageActor. In the USD section of the Details panel, locate the Level Sequence. Double-click the asset to open it in Sequencer.

   Double click the Level Sequence in the Details panel. Click image for full size.

For more information on using Sequencer, see Cinematics and Sequencer.

Animating the Chair

To add animation to the new prim ChairB_3 that you created in step three, you will create a new USD file and add it as a layer to the USD Stage Actor.

1. In the Layers section of the USD Stage window, right-click the kitchen_set.usd layer and select Add New. Save this new file as myanim.usda.

   Add a new Layer to your USD data for the animation. Click image for full size.

2. USD layers use a LIVRPS structure to determine how layers affect the final composition of the scene. For animation to affect the kitchen set, the layer containing that animation must be higher in the layer structure than the scene containing the prims. From the Top Menu in the Level Editor, select Window > Place Actors to open the panel. Search for Usd Stage Actor in the Place Actors panel and drag a new copy into your Level.

   New USD Actors in the Place Actors panel. Click image for full size.

3. Select the UsdStageActor in the Outliner. From the USD Stage panel, select File > Open and browse to your myanim.usda file.

4. Add the kitchen set back into the layer stack by right-clicking the myanim.usda layer and selecting the Add Existing option. In the File window, navigate to your kitchen_set.usd file and click Open.

5. Before adding the animation, the USD Stage needs to know how long the animation will be. Click the Stage prim in the hierarchy. In the Properties section, change the endTimeCode and endFrame values to 48.

   Change the endTimeCode and endFrame properties. Click image for full size.

6. Select your new USD Stage Actor in the Outliner. From the Details panel, scroll down to the USD section and locate Level Sequence. Double-click the asset to open it in Sequencer.

7. In the Sequencer panel, click the + Track button and select the Actor you want to animate from the Actor to Sequencer submenu.

   Add a new Track group for the selected Actor. Click image for full size.

8. Click the Add (+) button on the new track and create a new Transform track.

   Add a new Transform track. Click image for full size.

9. Animate the chair rotating in place. For more information on using Tracks in Sequencer, see Tracks.

10. Write the data back to USD using File > Save in the USD Stage window.

6. Importing Assets into an Unreal Engine Project

Actors displayed on the USD Stage Actor can be imported into the Unreal Editor's Content Browser through any of the following import options.

• Using File > Import Into Level. This process will import both assets (static mesh, skeletal mesh, materials, textures, and so on) and Actors.
• Using the Add/Import button in the Content Browser. This process will only import assets.
• Dragging and dropping the file into the Content Browser. This process will only import assets.
• Using the Action > Import option in the USD Stage Editor window. This process will import everything on the USD Stage Actor and works with both assets and Actors. After the import process is complete, assets on the USD Stage are replaced with new Actors from the Content Browser.

Importing the Kitchen Set into Unreal Engine

1. With the Kitchen Set open in the USD Stage window, open the Actions menu and select Import.

2. Select the location to store the imported assets. In this example, importing the Kitchen Set will create a folder named Kitchen_set in the selected location. Materials and static meshes are saved into separate subfolders.