Description

This PR builds on top of #2703 and #2733, which respectively added the notion of local isolated computations for nodes, and the concept of plugins. This pull request adds the notion of runtime-specific environment, allowing nodes to be executed in a dedicated environment that contains their required dependencies independently from Meshroom's.

Two types of execution environments are added in this PR:

1. DirTreeProcessEnv

Based on the root folder of the plugin, it sets up the environment (PYTHONPATH, PATH and LD_LIBRARY_PATH environment variables). It assumes the plugin has a standard hierarchy:

mrPlugin/
|-- bin
|-- lib
|   `-- pythonX.X
|       `-- site-packages
|           |-- anotherModule
|           `-- myCustomModule
`-- meshroom
    |-- myNodes
    |   |-- NodeA.py
    |   |-- NodeB.py
    |   |-- NodeC.py
    |   `-- __init__.py
    |-- myPipelineA.mg
    `-- myPipelineB.mg

To declare a plugin using the DirTree, set the env variable MESHROOM_PLUGINS_PATH.

2. RezProcessEnv

Based on a Rez package that's provided through a dedicated environment variable, it gathers all the requirements to execute the process within that Rez environment.

To declare plugins using Rez for their execution, use the MESHROOM_REZ_PLUGINS environment variable.

Rez plugins need to be provided to MESHROOM_REZ_PLUGINS with the following syntax: packageName=/path/to/root. Their package.py also need to follow a certain structure. An example is given below for a package named "mrExample":

name="mrExample"
version="1.0"

plugin_for=["meshroom"]
requires = []

def commands():
    subRequires = [
        'python-3',
        'dependency1-1.0',
        'dependency2-1.0',
        'dependency3'
    ]
    env.MESHROOM_REZ_PLUGINS.append(this.name + "={root}/folder")
    env.MREXAMPLE_SUBREQUIRES = ":".join(subRequires)

Features list

• Add a new MESHROOM_REZ_PLUGINS environment variable to load Rez plugins;
• Use an isolated and node-specific runtime environment for all the nodes.

Implementation remarks

For Rez plugins, a few things are to be noted:

1. Meshroom's ability to detect and set up the runtime environment for Rez plugins relies on the "name=path" pair being correctly provided to MESHROOM_REZ_PLUGINS.
2. Setting env.MRNAME_SUBREQUIRES in the Rez package's package.py is necessary, as it is used by Meshroom to list the dependencies.
3. Providing versions of packages for the subrequires is not mandatory: if a version is provided, it will strictly be respected; otherwise, Meshroom will attempt to match the package's version with its own, if it exists in its environment.
4. When the node is executed in its dedicated Rez environment, both Meshroom's path and the Rez package's are injected into the PYTHONPATH environment variable, strictly within the Rez environment.