Warning This is probably my first CMake/C++ project, you might see some things that could be better or are simply wrong, so please take it with a pinch of salt. PRs are highly appreciated.

USD Multi Asset Resolver

An ArResolver plugin for USD. This project aims to provide a wide range of tools to make the asset resolution on USD much more flexible. The resolver can be configured with stacks of sub-solvers that will perform tasks on the asset path such as expanding environment variables or performing a REST query to retrieve asset paths from a database (and in the future, possibly more).

Usage

The asset resolver can be configured with stacks of sub-solvers that will pick up the output of the previous sub-solver and pass its result to the next one until the asset path is fully resolved.

Available subsolvers

Name	Purpose	Implemented?
env	Expands environment variables	Yes
rest	Makes a GET request to a URL	Yes
format	Parses and re-formats	Yes
symlink	Expands symlinks	Yes
subprocess	Resolves the path via a subprocess	Yes
cache	Caches values to be baked for the farm	Planned

Configuration

The solver is configured by specifying the path to a JSON file via the environment variable USDMAR_CONFIG_PATH with the following format:

{
    "stacks": {
        "<stack name>": {
            "resolvers": [
                {
                    "type": "<subsolver type>",
                    "<subsolver var>": "<value>"
                }
            ]
        }
    },
    "defaults": {
        "<scheme>": "<stack>"
    }
}

Under stacks, a mapping of stacks can be defined, each one with its own list of resolvers. Resolvers can also specify their own variables. The defaults key makes defining the default stack to use in the asset path optional, for more information see the next section.

Schemes

The asset path is composed of three elements: <scheme>:<stack>!<path>, where scheme is the defined scheme at build time (by default mr), stack is the name of the stack to use and path is the asset path itself to be resolved. On the next section there are examples on it's usage.

Example

The following configuration file will do the following:

Convert a path in the format of /{project}/seq/{sequence}/{shot}/{asset}/{version}@ to a valid URL
Make a GET request to a local REST server
Expand any environment variables on the path

{
    "resolvers": {
        "db": {
            "stack": [
                {
                    "type": "format",
                    "pairs": [
                        [
                            "/([\\w\\d]+)/(?:seq|build)/([\\w\\d_]+)/([\\w\\d_]+)/([\\w\\d_]+)/([\\w\\d_]+)",
                            "?project={0}&sequence={1}&shot={2}&asset={3}&version={4}"
                        ]
                    ]
                },
                {
                    "type": "rest",
                    "host": "http://127.0.0.1:5000",
                    "entryPoint": "/api/v3"
                },
                {
                    "type": "env"
                }
            ]
        }
    },
    "defaults": {
        "mr": "db"
    }
}

To test this, we can create this USD file and run a simple Flask server on localhost with port 5000. Please note that because we've defined in the defaults section the scheme mr:, the asset path specified would be equivalent to it without the db! specification: @mr:/AHB/seq/NJS/0010/boat_aa/latest@.

#usda 1.0
(
)

def "geo" (
	references = [
        @mr:db!/AHB/seq/NJS/0010/boat_aa/latest@
    ]
    ) {
}

We can set the environment variable TF_DEBUG to USDMAR" to get a better feeling of what's going on:

usdmar - MultiResolver::_Resolve('mr:db!/AHB/seq/NJS/0010/boat_aa/latest')
usdmar - Extracted asset path: /AHB/seq/NJS/0010/boat_aa/latest
usdmar - [RESTSubSolver::Resolve] Making GET request to url 'http://127.0.0.1:5000/api/v3?project=AHB&sequence=NJS&shot=0010&asset=boat_aa&version=latest'
usdmar - [RESTSubSolver::Resolve] Response: ${PROJECTS_ROOT}/AHB/publish/seq/NJS/0010/boat_aa/v005/main.usda
usdmar - Resolving /AHB/seq/NJS/0010/boat_aa/latest:
        format    -> ?project=AHB&sequence=NJS&shot=0010&asset=boat_aa&version=latest
        rest      -> ${PROJECTS_ROOT}/AHB/publish/seq/NJS/0010/boat_aa/v005/main.usda
        env       -> /mnt/projects/AHB/publish/seq/NJS/0010/boat_aa/v005/main.usda

Building

Build command

The easiest way to build it is to compile USD and use the flags to automatically download and build the missing of dependencies:

git clone https://github.com/salvaom/usd-mar
cd usd-mar
mkdir build
cd build
cmake -DCMAKE_PREFIX_PATH=<USD INSTALL PATH> -G "<GENERATOR NAME>" -DDOWNLOAD_CPR=ON -DDOWNLOAD_SUBPROCESSH=ON ..

Build requirements:

Name	Optional	Version
USD	No	22.08
CPR	Yes	1.9.1
subprocess.h	Yes	master?
Python	No, planned	3.7.x

Build Options

Option	Function	Default
USDMAR_REST	Whether to build with support for the REST subsolver Requires CRP	ON
USDMAR_SUBPROCESS	Whether to build with support for the subprocess subsolver Requires subprocess.h	ON
DOWNLOAD_CPR	Downloads and builds CPR	OFF
DOWNLOAD_SUBPROCESSH	Downloads subprocess.h	OFF
RESOLVER_SCHEMES	List of schemes (space separated) to register for asset resolution	`mr`