End to End Example
VERIFIED ON USD VERSION 21.05
This tutorials aims to show USD in an extremely simplified pipeline. The files for this tutorial live in USD/extras/usd/tutorials/endToEnd.
Overview of files:
- assets: This folder contains some files that are used in the tutorial. It also contains some of the geometry in case you do not want to author them yourself.
- scripts: Some generic scripts we use in the tutorial. We've tried to document them. Feel free to poke around, or run them with
- tutorial_scripts: Scripts specifically geared toward this tutorial. They may have hard-coded paths that are intended to be run from the tutorial root. We've also documented those, but they are intended to be used primarily for this tutorial.
- How to generate USD files from Maya
- How to introspect USD files
- How to manipulate USD files with code
We'll first run a script that bootstraps an asset for us. The following will create an empty asset named "Ball" inside the directory "models/Ball".
Go ahead and look at the files it created:
There is no geometry but if
usdview opens without errors, we're off to a great start. We'll be adding geometry in the next section.
Putting models in their own directories is convenient for managing versions, etc. but how you layout files at your site will likely differ. This particular structure is an example and is not required to get USD to work.
We're going to also need a Table for this example so go ahead and run:
The Maya plugin previously distributed with USD has been incorporated into the Autodesk maya-usd repository. This portion of the tutorial remains here for historical reference.
You can continue through this tutorial by using the geometry provided in the repository and skipping to the "Shading Variants" section.
You should see a sphere-like mesh for the Ball asset.
Load the Maya plugin
Inside Maya, load the
pxrUsd Maya plugin. This can be done via the Plug-in Manager
(Windows -> Settings/Preferences -> Plug-in Manager) or by entering the following command in the MEL script window
Exporting the ball asset
Open the Ball.ma file in Maya. This file contains geometry and shading for a simple sphere:
To export this scene, select the sphere, select
File -> Export Selection, and choose pxrUsdExport under Files of type.
Be sure to choose RfM under shading mode. In the file browser, find "
models/Ball/Ball.maya.usd" and save over it.
You can now try viewing this:
Exporting the table asset
Open the Table.ma file in Maya.
Select the table in the scene, then select
File -> Export Selection. Choose pxrUsdExport under Files of type.
As with the Ball, be sure to choose RfM under shading mode. In the file browser, find "
models/Table/Table.maya.usd" and save over it.
At this point, you should have geometry and shading information authored for both the
Table. If you were not able to complete this section, see the note above for instructions on copying over pre-exported assets.
We will add shading variants to the Ball entirely through code. Please see
Start by copying the Ball textures into your Ball directory:
Add shading variants to the Ball with a python script:
This script assumes you've been following along the tutorial and is expecting a
Ball model to exist with shading from the Maya file. If you've tweaked things, you may have to go in and modify that script.
We are keeping the networks very simple for this tutorial. If you look at the
Ball model in
usdview, and then with
/Ball selected, select the Meta Data tab and use the shadingVariant drop-down menu to change to variants with different colors.
We'll create a set model that brings together the
Table and a standard set of 15
Ball models together.
This script assumes you've been following along the tutorial and is expecting an
Table model to exist. It also makes some assumptions about the size of these models. If you've tweaked things, you may have to go in and modify that script.
Also, note that we're hard-coding absolute paths to the other assets. The path resolver plugin provides a better mechanism that allows you to locate assets by other means.
You may need to move the camera around to see the table and balls as pictured below.
Here, we'll mock up an example of how a sequence and shot might be structured. This will illustrate some of the benefits of USD composition. Since your structure likely varies, we'll first define some terms and explain the structure we're about to create.
A sequence is a collection of related shots. A shot will include (by sublayering) all the scene description that is associated with its sequence. This structure allows you to put opinions that affect multiple shots in one location. We will also make each sequence inherit opinions from a global/shared
shot.usd file. This makes it so we can define the overall structure in one place. That's a good place to put things you will need everywhere (for example, the camera).
Another axis by which we organize our work is by department. A shot can have a layer for layout, a layer for animation, and a layer for sim, as an example. The same goes for a sequence. We will build a shot that has the following layers (strongest to weakest)
USD has no notion of what a "shot" or "sequence" is. Again, this is just an example and this structure is not required for USD.
scripts/create_shot.py script will help setup a sequence and a shot. For starters, take a look at the structure that's defined in
Let's setup the sequence. We'll use the
create_shot.py script even though we're making a sequence:
This creates a sequence in the directory
shots/s00 that references
assets/shot.usd (note the
-b argument to
create_shot.py authors that reference verbatim).
And now the shot:
Now, you should have the layer structure defined in the previous sections. Opinions from the shot will override the weaker opinions that are in the sequence or the "global" layer.
In an actual production, you'll probably structure your files to make the dependency between
s00 more evident.
Since this is a newly created shot and sequence, there shouldn't really be anything in it except for what was in assets/shot.usd, which should just be the camera.
Simple shot work
Now we'll start running some scripts. First, at the sequence level, we'll bring in the
And now, let's say a layout TD adds in a cue ball, removes some un-needed props, and positions the camera
The Katana USD plugin was removed from the USD distribution in version 20.05 in favor of the Foundry-supported plugin located at https://github.com/TheFoundryVisionmongers/KatanaUsdPlugins. This portion of the tutorial remains here for historical reference.
We'll now render our shot in
katana. In the root of your endToEnd tutorial directory, run:
The USD file is read in with the provided PxrusdIn node. An optional camera is merged into the scene (to work around a known issue when rendering from the camera in the USD file). A simple light is created in the gaffer node.
To render the scene, right-click on the RenderSettings node and select "Preview Render".
Feel free to experiment with this tutorial by modifying scripts or adding your own geometry and shading.