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redhot - pyo3 (python + rust) auto-reloading for TouchDesigner

This is a little COMP to make your life easier when integrating Rust into your extensions

tl;dr

Let's assume you've got:

  • A TouchDesigner project with a project folder
  • A Python venv under $PROJECT/.venv
  • A Rust installation
  • You are on MacOS (untested on Windows but feel free and lmk!)

And you want:

  • To develop a Rust extension with Python bindings usable in TD
  • Have it automatically rebuild and reload when you re-init your TD extensions, scripts, etc

This COMP sets that up for you!

Usage

  • With the venv activated run pip install maturin maturin-import-hook

  • Run maturin new <name> inside your project folder

    • Creates a pyo3 package which will contain your Rust code
    • This name is what you'll be importing in Python-land

  • Run cd <name>; maturin develop --release

    • Builds and installs the package into the venv
    • Should only be necessary once

  • Grab redhot.tox and drop it into TouchDesigner

    • Sets up the environment and some magic hooks

  • Import your package like so

    import importlib
import <name>  # careful: your Rust module will be exposed under `<name>.<name>`
importlib.reload(<name>)

    The reload call normally has no effect on native code, but now it will rebuild and reinstall your package if there were any changes, and force the Python interpreter to actually reload it from disk!

    • check for output in the Textport
    • note that while a rebuild is happening the TD process will hang. This should only happen when you've edited Rust code and then enabled/disabled your COMP/script, re-inited, etc

Motivation

pyo3 is great and gives us an easy way to integrate Rust into Python projects. The only catch is that CPython can't reload native extensions, requiring you to restart the interpreter when you make changes. Bad news for TouchDesigner - you'd have to restart the whole app as part of your feedback loop!

More background on this can be found at maturin-import-hook/docs/reloading.md, if you're interested.

Solution

This COMP uses maturin-import-hook which includes some clever tricks to force the Python interpreter into reloading pyo3 extensions properly. The hook also provides conveniences for auto-building etc, so it makes sense to try to use it.

How It Works

On RedhotExt init we do some preliminary setup of the environment:

  • TouchDesigner doesn't inherit the system path, at least on MacOS, so we need to add $HOME/.cargo/bin to the PATH so that the rustc command is available
  • We need to ensure the venv you're using (which is assumed to be in the project folder under .venv and to have maturin and maturin-import-hook installed!) is also in the PATH
  • The venv also needs to be added to the Python search path, which is done by appending to sys.path

After that it's just a call to maturin_import_hook.install() and the hook handles everything