nih-plug/src/plugin.rs

// nih-plug: plugins, but rewritten in Rust
// Copyright (C) 2022 Robbert van der Helm
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

use std::pin::Pin;

use crate::params::Params;

/// Basic functionality that needs to be implemented by a plugin. The wrappers will use this to
/// expose the plugin in a particular plugin format.
///
/// This is super basic, and lots of things I didn't need or want to use yet haven't been
/// implemented. Notable missing features include:
///
/// - MIDI
/// - Sidechain inputs
/// - Multiple output busses
/// - Latency compensation
/// - Special handling for offline processing
/// - Transport and other context information in the process call
/// - Storing custom state, only the parameters are saved right now
/// - Sample accurate automation (this would be great, but sadly few hosts even support it so until
///   they do we'll ignore that it's a thing)
/// - Parameter update callbacks
/// - Parameter hierarchies/groups
/// - Bypass parameters, right now the VST3 wrapper generates one for you
/// - Outputting parameter changes from the plugin
/// - GUIs
pub trait Plugin: Default + Sync {
    const NAME: &'static str;
    const VENDOR: &'static str;
    const URL: &'static str;
    const EMAIL: &'static str;

    /// Semver compatible version string (e.g. `0.0.1`). Hosts likely won't do anything with this,
    /// but just in case they do this should only contain decimals values and dots.
    const VERSION: &'static str;

    /// The default number of inputs. Some hosts like, like Bitwig and Ardour, use the defaults
    /// instead of setting up the busses properly.
    const DEFAULT_NUM_INPUTS: u32;
    /// The default number of inputs. Some hosts like, like Bitwig and Ardour, use the defaults
    /// instead of setting up the busses properly.
    const DEFAULT_NUM_OUTPUTS: u32;

    /// The plugin's parameters. The host will update the parameter values before calling
    /// `process()`. These parameters are identified by strings that should never change when the
    /// plugin receives an update.
    ///
    /// TODO: Rethink the API a bit more. Also Requiring the pin on self makes more sense, but it's
    ///       not strictly necessary. We'll have to change this once the API is usable to see what's
    ///       ergonmic.
    fn params(&self) -> Pin<&dyn Params>;

    //
    // The following functions follow the lifetime of the plugin.
    //

    /// Whether the plugin supports a bus config. This only acts as a check, and the plugin
    /// shouldn't do anything beyond returning true or false.
    fn accepts_bus_config(&self, config: &BusConfig) -> bool;

    /// Initialize the plugin for the given bus and buffer configurations.
    ///
    /// Before this point, the plugin should not have done any expensive initialization. Pleaes
    /// don't be that plugin that takes twenty seconds to scan.
    fn initialize(&mut self, bus_config: &BusConfig, buffer_config: &BufferConfig) -> bool;

    /// Process audio. To not have to worry about aliasing, the host's input buffer have already
    /// been copied to the output buffers if they are not handling buffers in place (most hosts do
    /// however).
    ///
    /// TODO: &mut [&mut [f32]] may not be the correct type here
    /// TODO: Provide a way to access auxiliary input channels if the IO configuration is
    ///       assymetric
    /// TODO: Handle FTZ stuff on the wrapper side and mention that this has been handled
    /// TODO: Pass transport and other context information to the plugin
    fn process(&mut self, samples: &mut [&mut [f32]]) -> ProcessStatus;
}

/// Provides auxiliary metadata needed for a VST3 plugin.
pub trait Vst3Plugin: Plugin {
    /// The unique class ID that identifies this particular plugin. You can use the
    /// `*b"fooofooofooofooo"` syntax for this.
    const VST3_CLASS_ID: [u8; 16];
    /// One or more categories, separated by pipe characters (`|`), up to 127 characters. Anything
    /// logner than that will be truncated. See the VST3 SDK for examples of common categories:
    /// https://github.com/steinbergmedia/vst3_pluginterfaces/blob/2ad397ade5b51007860bedb3b01b8afd2c5f6fba/vst/ivstaudioprocessor.h#L49-L90
    const VST3_CATEGORIES: &'static str;
}

/// We only support a single main input and output bus at the moment.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct BusConfig {
    /// The number of input channels for the plugin.
    pub num_input_channels: u32,
    /// The number of output channels for the plugin.
    pub num_output_channels: u32,
}

/// Configuration for (the host's) audio buffers.
#[derive(Debug, Clone, PartialEq)]
pub struct BufferConfig {
    /// The current sample rate.
    pub sample_rate: f32,
    /// The maximum buffer size the host will use. The plugin should be able to accept variable
    /// sized buffers up to this size.
    pub max_buffer_size: u32,
}

/// Indicates the current situation after the plugin has processed audio.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ProcessStatus {
    /// Something went wrong while processing audio.
    Error(&'static str),
    /// The plugin has finished processing audio. When the input is silent, the most may suspend the
    /// plugin to save resources as it sees fit.
    Normal,
    /// The plugin has a (reverb) tail with a specific length in samples.
    Tail(u32),
    /// This plugin will continue to produce sound regardless of whether or not the input is silent,
    /// and should thus not be deactivated by the host. This is essentially the same as having an
    /// infite tail.
    KeepAlive,
}