Add the basic plugin API

src/lib.rs

@@ -15,3 +15,4 @@
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 pub mod params;
+pub mod plugin;

src/plugin.rs

@@ -0,0 +1,92 @@
+// nih-plugs: 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
+/// - 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
+/// - Outputting parameter changes from the plugin
+/// - GUIs
+pub trait Plugin: Sync {
+    /// 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 &[f32]] may not be the correct type here
+    /// TODO: Provide a way to access auxiliary input channels if the IO configuration is
+    ///       assymetric
+    fn process(&mut self, samples: &mut &[f32]);
+}
+
+/// We only support a single main input and output bus at the moment.
+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.
+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,
+}