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Custom Schemas

How-to create a USD custom schema.

Important Links

Note

You can find the usdFxquinox plugin on GitHub .

The easiest way to create a custom schema is to create what’s called a codeless schema (uncompiled version). This will create a new schema but won’t provide the C++/Python bindings from the freshly created schema class.

Directory Structure

Let’s start by creating a directory and a schema.usda file:

Directory 
.
└── 📁 usdFxquinox/
    └── 📁 resources/
        └── 📁 usdFxquinox/
            └── 📄schema.usda

Which corresponds to:

Directory 
.
└── 📁 <plugin name>/
    └── 📁 resources/
        └── 📁 <plugin name>/
            └── 📄 schema.usda

Edit schema.usda

Let’s now edit our schema.usda file. This will contain the IsA schemas or API schemas you want to create.

schema.usda 
#usda 1.0
(
    subLayers = [
        @usd/schema.usda@
    ]
)

over "GLOBAL" (
    customData = {
        string libraryName       = "usdFxquinox"
        string libraryPath       = "."
        string libraryPrefix     = "usdFxquinox"
        bool skipCodeGeneration = true
    }
)
{
}

class FxquinoxContextInfo "FxquinoxContextInfo" (
    doc = """Holder for fxquinox-specific context information."""
    inherits = </Typed>
    customData = {
        string className = "ContextInfo"
        }
    )
{
    string fxquinox:project (
        doc = """The project name."""
    )

    asset fxquinox:projectRoot (
        doc = """The project root path."""
    )

    string fxquinox:entity (
        doc = """The current context entity (asset or shot)."""
    )

    string fxquinox:assetType (
        doc = """If the entity is an asset, the type of asset."""
    )

    string fxquinox:asset (
        doc = """If the entity is an asset, the asset."""
    )

    string fxquinox:sequence (
        doc = """If the entity is a shot, the sequence."""
    )

    string fxquinox:shot (
        doc = """If the entity is a shot, the shot."""
    )

    string fxquinox:step (
        doc = """The context pipeline step."""
    )

    string fxquinox:task (
        doc = """The context pipeline task."""
    )

    string fxquinox:user (
        doc = """The current username."""
    )

    string fxquinox:hostname (
        doc = """The current hostname (machine name)."""
    )
}

Run usdGenSchema

Once you’re happy with your new schema, we now need to run usdGenSchema. The easiest way is to run the one shipping with your DCC compiled USD.

I made this batch script to run it on Windows:

.run_usdGenSchema.bat 
@echo off

REM Set paths to Houdini programs, and the USD file
set HOUDINI_VERSION=20.0.547
set USD_PLUGIN_NAME=usdFxquinox
set HYTHON_PATH="C:\Program Files\Side Effects Software\Houdini %HOUDINI_VERSION%\bin\hython.exe"
set USDGENSCHEMA_PATH="C:\Program Files\Side Effects Software\Houdini %HOUDINI_VERSION%\bin\usdGenSchema"
set SCHEMA_PATH=%~dp0%USD_PLUGIN_NAME%\schema.usda
set DESTINATION_PATH=%~dp0

echo Running usdGenSchema for %USD_PLUGIN_NAME%:
echo           Hython: %HYTHON_PATH%
echo       USD plugin: %USD_PLUGIN_NAME%
echo     UsdGenSchema: %USDGENSCHEMA_PATH%
echo           Schema: %SCHEMA_PATH%
echo             Dest: %DESTINATION_PATH%
echo.

REM Run the command `hython usdGenSchema 'path/to/schema.usda' 'destination/path'`
%HYTHON_PATH% %USDGENSCHEMA_PATH% %SCHEMA_PATH% %DESTINATION_PATH%

pause

Note

Think about changing your HOUDINI_VERSION and USD_PLUGIN_NAME accordingly.

Warning

%~dp0 is the Batch variable that expands to the current directory. Only use it if your .bat file is placed under the plugin folder: usdFxquinox/resources/_run_usdGenSchema.bat

Let the tool run. Once it’s done, you should have 2 new files:

Directory 
.
└── 📁 usdFxquinox/
    ├── 📁 resources/
    │   └── 📁 usdFxquinox/
    │       └── 📄 schema.usda
    ├── 📄 generatedSchema.usda
    └── 📄 plugInfo.json

You’ll need to modify the plugInfo.json file, since usdGenSchema leaves in the cmake @...@ string replacements:

plugInfo.json 
...
    "LibraryPath": "@PLUG_INFO_LIBRARY_PATH@",
    "Name": "usdFxquinox",
    "ResourcePath": "@PLUG_INFO_RESOURCE_PATH@",
    "Root": "@PLUG_INFO_ROOT@",
    "Type": "resource"
...

To:

plugInfo.json 
...
    "LibraryPath": "",
    "Name": "usdFxquinox",
    "ResourcePath": "resources",
    "Root": "..",
    "Type": "resource"
...

This change only need to be made once, as indicated in plugInfo.json :

plugInfo.json 
# Edits will survive regeneration except for comments and
# changes to types with autoGenerated=true.

Edit Environment

The last step is to add the folder containing plugInfo.json to the PXR_PLUGINPATH_NAME environment variable. In our instance: 

set PXR_PLUGINPATH_NAME=%SERVER_ROOT%/Projects/Code/fxquinox/plugins/usd/usdFxquinox/resources;%PXR_PLUGINPATH_NAME%