clack-plugin 0.2.0

Low-level, safe Rust wrappers to create audio plugins using the CLAP audio plugin API.
Documentation

A crate offering low-level, safe Rust wrappers to create audio plugins using the CLAP audio plugin API.

This library is made of lightweight, low-level wrappers built on top of clap-sys.

This is part of the Clack project. See the clack-host crate if you need to make CLAP hosts, and the clack-extensions crate that contains wrappers for all the standard CLAP extensions (for both plugins and hosts).

Features

  • Safe: The #1 goal of this project is to provide the full functionality of the CLAP plugin APIs through fully memory-safe and thread-safe wrappers.

    This allows for making safer, less crash-prone plugins, but also allows to fully trust Rust's type system when making large refactorings or performance optimizations, especially when dealing with CLAP's powerful, multithreaded model.

  • Low-level: When safe designs permit it, Clack aims to be as close as possible to the underlying CLAP C API. Whenever it is safe to do so, it does not make any assumptions or interpretations about any operation, and simply passes data through to the user.

    Anything that's possible to do with the CLAP C API, should also be possible to do using only safe Rust and Clack.

  • Lightweight: Considering the performance sensitivity of audio plugins, Clack aims to add as little overhead as possible to any operation (being a low-level library helps!). It reduces runtime checks and memory allocations to an absolute minimum, heavily leveraging zero-cost abstractions or user-provided buffers for example.

  • Extensible: Following the intent of the underlying CLAP API, Clack allows third-party users and crates to use, add, or extend extensions, event types, factories, and more. As a matter of fact, all extensions in the clack-extensions crate are implemented using tools all Clack users have access to, and users may add or replace the provided implementations with their own!

  • Reasonably defensive: While Clack performs very little extra sanity checks to keep its overhead as low as possible, it will report any erroneous behavior it stumbles upon to user code if possible, or just log it and fall back to the safest option otherwise (e.g. in case of panics originating from user code).

  • Fairly ergonomic: Despite Clack being a low-level, fast API, it also tries to provide some additional ergonomic APIs when wrapping the C APIs, as long as they don't have any impact on performance or low-level capability. Examples include using Rust's Option, Result, allowing the use of iterators, implementing standard traits for e.g. I/O, From implementations for buffer types, etc.

clack-plugin example

This example code implements a very simple gain plugin that amplifies every input by 2.0. More involved examples are available in the examples directory, and in the crate's documentation.

use clack_plugin::prelude::*;

pub struct MyGainPlugin;

impl Plugin for MyGainPlugin {
    type AudioProcessor<'a> = MyGainPluginAudioProcessor;

    type Shared<'a> = ();
    type MainThread<'a> = ();
}

impl DefaultPluginFactory for MyGainPlugin {
    fn get_descriptor() -> PluginDescriptor {
        PluginDescriptor::new("org.rust-audio.clack.gain", "Clack Gain Example")
    }

    fn new_shared(_host: HostSharedHandle<'_>) -> Result<Self::Shared<'_>, PluginError> {
        Ok(())
    }

    fn new_main_thread<'a>(
        _host: HostMainThreadHandle<'a>,
        _shared: &'a Self::Shared<'a>,
    ) -> Result<Self::MainThread<'a>, PluginError> {
        Ok(())
    }
}

pub struct MyGainPluginAudioProcessor;

impl<'a> PluginAudioProcessor<'a, (), ()> for MyGainPluginAudioProcessor {
    fn activate(_host: HostAudioProcessorHandle<'a>, _main_thread: &(), _shared: &'a (), _audio_config: PluginAudioConfiguration) -> Result<Self, PluginError> {
        Ok(Self)
    }

    fn process(&mut self, _process: Process, mut audio: Audio, _events: Events) -> Result<ProcessStatus, PluginError> {
        for mut port_pair in &mut audio {
            // For this example, we'll only care about 32-bit sample data.
            let Some(channel_pairs) = port_pair.channels()?.into_f32() else { continue; };

            for channel_pair in channel_pairs {
                match channel_pair {
                    ChannelPair::InputOnly(_) => {}
                    ChannelPair::OutputOnly(buf) => buf.fill(0.0),
                    ChannelPair::InputOutput(input, output) => {
                        for (input, output) in input.iter().zip(output) {
                            *output = input * 2.0
                        }
                    }
                    ChannelPair::InPlace(buf) => {
                        for sample in buf {
                            *sample *= 2.0
                        }
                    }
                }
            }
        }

        Ok(ProcessStatus::Continue)
    }
}

clack_export_entry!(SinglePluginEntry<MyGainPlugin>);

Compiling this code as a "cdylib" library crate will produce a CLAP-compliant dynamic library file in your project's target folder.

License

This crate is distributed under the terms of both the MIT license and the Apache license, version 2.0. Contributions are accepted under the same terms.