Add MIDI IO support to the CPAL backends

Using Midir. This has been on the todo list for way too long.

src/wrapper/standalone/backend/cpal.rs

@@ -1,22 +1,28 @@
-use std::num::NonZeroU32;
-
 use anyhow::{Context, Result};
 use cpal::{
     traits::*, Device, InputCallbackInfo, OutputCallbackInfo, Sample, SampleFormat, Stream,
     StreamConfig,
 };
 use crossbeam::sync::{Parker, Unparker};
-use midir::{MidiInput, MidiInputPort, MidiOutput, MidiOutputPort};
+use midir::{
+    MidiInput, MidiInputConnection, MidiInputPort, MidiOutput, MidiOutputConnection, MidiOutputPort,
+};
 use parking_lot::Mutex;
 use rtrb::RingBuffer;
+use std::borrow::Borrow;
+use std::num::NonZeroU32;
+use std::thread::ScopedJoinHandle;
 
 use super::super::config::WrapperConfig;
 use super::Backend;
 use crate::audio_setup::{AudioIOLayout, AuxiliaryBuffers};
 use crate::buffer::Buffer;
 use crate::context::process::Transport;
-use crate::midi::{MidiConfig, PluginNoteEvent};
+use crate::midi::{MidiConfig, MidiResult, PluginNoteEvent};
 use crate::plugin::Plugin;
+use crate::prelude::NoteEvent;
+
+const MIDI_EVENT_QUEUE_CAPACITY: usize = 2048;
 
 /// Uses CPAL for audio and midir for MIDI.
 pub struct CpalMidir {
@@ -26,8 +32,8 @@ pub struct CpalMidir {
     input: Option<CpalDevice>,
     output: CpalDevice,
 
-    midi_input: Option<Mutex<MidirInputDevice>>,
-    midi_output: Option<Mutex<(MidirOutputDevice)>>,
+    midi_input: Mutex<Option<MidirInputDevice>>,
+    midi_output: Mutex<Option<MidirOutputDevice>>,
 }
 
 /// All data needed for a CPAL input or output stream.
@@ -41,8 +47,12 @@ struct CpalDevice {
 struct MidirInputDevice {
     pub backend: MidiInput,
     pub port: MidiInputPort,
-    // The name can be retrieved from the port, not sure why the connect function needs the name
-    // again
+}
+
+/// An active `MidirInputDevice`. Transformed back and from this during the `.run()` function.
+struct ActiveMidirInputDevice {
+    pub connection: MidiInputConnection<()>,
+    pub port: MidiInputPort,
 }
 
 /// All data needed to create a Midir output stream.
@@ -51,6 +61,20 @@ struct MidirOutputDevice {
     pub port: MidiOutputPort,
 }
 
+/// An active `MidirOutputDevice`. Transformed back and from this during the `.run()` function.
+struct ActiveMidirOutputDevice {
+    pub connection: MidiOutputConnection,
+    pub port: MidiOutputPort,
+}
+
+/// A task for the MIDI output thread.
+enum MidiOutputTask<P: Plugin> {
+    /// Send an event as MIDI data.
+    Send(PluginNoteEvent<P>),
+    /// Terminate the thread, stopping it from blocking and allowing it to be joined.
+    Terminate,
+}
+
 impl<P: Plugin> Backend<P> for CpalMidir {
     fn run(
         &mut self,
@@ -64,96 +88,253 @@ impl<P: Plugin> Backend<P> for CpalMidir {
             + 'static
             + Send,
     ) {
-        // The CPAL audio devices may not accept floating point samples, so all of the actual audio
+        // So this is a lot of fun. There are up to four separate streams here, all using their own
+        // callbacks. The audio output stream acts as the primary stream, and everything else either
+        // sends data to it or (in the case of the MIDI output stream) receives data from it using
+        // channels.
+        //
+        // Audio input is read from the input device (if configured), and is send at a period at a
+        // time to the output stream in an interleaved format. Because of that the audio output
+        // stream is delayed for one period using a parker to you don't immediately get xruns. CPAL
+        // audio devices may also not accept floating point samples, so all of the actual audio
         // handling and buffer management handles in the `build_*_data_callback()` functions defined
         // below.
+        //
+        // MIDI input is parsed in the Midir callback and the events are sent over a callback to the
+        // output audio thread where the process callback happens. If that process callback outputs
+        // events then those are sent over another ringbuffer to a thread that handles MIDI output.
+        // Both MIDI input and MIDI output are disabled by default.
+        //
+        // The thread scope is needed to accomodate the midir MIDI output API. Outputting MIDI is
+        // realtime unsafe, and to be able to output MIDI with midir you need to transform between
+        // `MidiOutputPort` and `MidiOutputPortConnection` types by taking values out of an
+        // `Option`.
+        std::thread::scope(|s| {
+            let mut _input_stream: Option<Stream> = None;
+            let mut input_rb_consumer: Option<rtrb::Consumer<f32>> = None;
+            if let Some(input) = &self.input {
+                // Data is sent to the output data callback using a wait-free ring buffer
+                let (rb_producer, rb_consumer) = RingBuffer::new(
+                    self.output.config.channels as usize * self.config.period_size as usize,
+                );
+                input_rb_consumer = Some(rb_consumer);
 
-        // CPAL does not support duplex streams, so audio input (when enabled, inputs aren't
-        // connected by default) waits a read a period of data before starting the output stream
-        let mut _input_stream: Option<Stream> = None;
-        let mut input_rb_consumer: Option<rtrb::Consumer<f32>> = None;
-        if let Some(input) = &self.input {
-            // Data is sent to the output data callback using a wait-free ring buffer
-            let (rb_producer, rb_consumer) = RingBuffer::new(
-                self.output.config.channels as usize * self.config.period_size as usize,
-            );
-            input_rb_consumer = Some(rb_consumer);
+                let input_parker = Parker::new();
+                let input_unparker = input_parker.unparker().clone();
+                let error_cb = {
+                    let input_unparker = input_unparker.clone();
+                    move |err| {
+                        nih_error!("Error during capture: {err:#}");
+                        input_unparker.clone().unpark();
+                    }
+                };
 
-            let input_parker = Parker::new();
-            let input_unparker = input_parker.unparker().clone();
+                let stream = match input.sample_format {
+                    SampleFormat::I16 => input.device.build_input_stream(
+                        &input.config,
+                        self.build_input_data_callback::<i16>(input_unparker, rb_producer),
+                        error_cb,
+                    ),
+                    SampleFormat::U16 => input.device.build_input_stream(
+                        &input.config,
+                        self.build_input_data_callback::<u16>(input_unparker, rb_producer),
+                        error_cb,
+                    ),
+                    SampleFormat::F32 => input.device.build_input_stream(
+                        &input.config,
+                        self.build_input_data_callback::<f32>(input_unparker, rb_producer),
+                        error_cb,
+                    ),
+                }
+                .expect("Fatal error creating the capture stream");
+                stream
+                    .play()
+                    .expect("Fatal error trying to start the capture stream");
+                _input_stream = Some(stream);
+
+                // Playback is delayed one period if we're capturing audio so it has something to
+                // process
+                input_parker.park()
+            }
+
+            // The output callback can read input events from this ringbuffer
+            let mut midi_input_rb_consumer: Option<rtrb::Consumer<PluginNoteEvent<P>>> = None;
+            let midi_input_connection: Option<ActiveMidirInputDevice> =
+                self.midi_input.lock().take().and_then(|midi_input| {
+                    // Data is sent to the output data callback using a wait-free ring buffer
+                    let (rb_producer, rb_consumer) = RingBuffer::new(MIDI_EVENT_QUEUE_CAPACITY);
+                    midi_input_rb_consumer = Some(rb_consumer);
+
+                    let result = midi_input.backend.connect(
+                        &midi_input.port,
+                        "MIDI input",
+                        self.build_midi_input_thread::<P>(rb_producer),
+                        (),
+                    );
+
+                    match result {
+                        Ok(connection) => Some(ActiveMidirInputDevice {
+                            connection,
+                            port: midi_input.port,
+                        }),
+                        Err(err) => {
+                            // We won't retry once this fails
+                            nih_error!("Could not create the MIDI input connection: {err:#}");
+                            midi_input_rb_consumer = None;
+
+                            None
+                        }
+                    }
+                });
+
+            // The output callback can also emit MIDI events. To handle these we'll need to spawn
+            // our own thread. This can be simplified a lot by using the `MidiOutputConnection`
+            // directly inside the audio output callback, but looking at the implementation sending
+            // MIDI events is not realtime safe in most midir backends.
+            // NOTE: This uses crossbeam channels instead of rtrb specifically for the optional
+            //        blocking API. This lets the MIDI sending thread sleep when there's no work to
+            //        do.
+            let mut midi_output_rb_producer: Option<crossbeam::channel::Sender<MidiOutputTask<P>>> =
+                None;
+            let midi_output_connection: Option<ScopedJoinHandle<ActiveMidirOutputDevice>> =
+                self.midi_output.lock().take().and_then(|midi_output| {
+                    // This uses crossbeam channels for the reason mentioned above, but to keep
+                    // things cohesive we'll use the same naming scheme as we use for rtrb
+                    let (sender, receiver) = crossbeam::channel::bounded(MIDI_EVENT_QUEUE_CAPACITY);
+                    midi_output_rb_producer = Some(sender);
+
+                    let result = midi_output
+                        .backend
+                        .connect(&midi_output.port, "MIDI output");
+
+                    match result {
+                        Ok(mut connection) => Some(s.spawn(move || {
+                            while let Ok(task) = receiver.recv() {
+                                match task {
+                                    MidiOutputTask::Send(event) => match event.as_midi() {
+                                        Some(MidiResult::Basic(midi_data)) => {
+                                            if let Err(err) = connection.send(&midi_data) {
+                                                nih_error!("Could not send MIDI event: {err}");
+                                            }
+                                        }
+                                        Some(MidiResult::SysEx(padded_sysex_buffer, length)) => {
+                                            // The SysEx buffer may contain padding
+                                            let padded_sysex_buffer = padded_sysex_buffer.borrow();
+                                            nih_debug_assert!(length <= padded_sysex_buffer.len());
+
+                                            if let Err(err) =
+                                                connection.send(&padded_sysex_buffer[..length])
+                                            {
+                                                nih_error!("Could not send MIDI event: {err}");
+                                            }
+                                        }
+                                        None => (),
+                                    },
+                                    MidiOutputTask::Terminate => break,
+                                }
+                            }
+
+                            // We'll return the same value from the join handle as what ends up
+                            // being stored in `midi_input_connection` to keep this symmetrical with
+                            // the input handling
+                            ActiveMidirOutputDevice {
+                                connection,
+                                port: midi_output.port,
+                            }
+                        })),
+                        Err(err) => {
+                            nih_error!("Could not create the MIDI output connection: {err:#}");
+                            midi_output_rb_producer = None;
+
+                            None
+                        }
+                    }
+                });
+
+            // This thread needs to be blocked until audio processing ends as CPAL processes the
+            // streams on another thread instead of blocking
+            let parker = Parker::new();
+            let unparker = parker.unparker().clone();
             let error_cb = {
-                let input_unparker = input_unparker.clone();
+                let unparker = unparker.clone();
                 move |err| {
-                    nih_error!("Error during capture: {err:#}");
-                    input_unparker.clone().unpark();
+                    nih_error!("Error during playback: {err:#}");
+                    unparker.clone().unpark();
                 }
             };
 
-            let stream = match input.sample_format {
-                SampleFormat::I16 => input.device.build_input_stream(
-                    &input.config,
-                    self.build_input_data_callback::<i16>(input_unparker, rb_producer),
+            let output_stream = match self.output.sample_format {
+                SampleFormat::I16 => self.output.device.build_output_stream(
+                    &self.output.config,
+                    self.build_output_data_callback::<P, i16>(
+                        unparker,
+                        input_rb_consumer,
+                        midi_input_rb_consumer,
+                        // This is a MPMC crossbeam channel instead of an rtrb ringbuffer, and we
+                        // also need it to terminate the thread
+                        midi_output_rb_producer.clone(),
+                        cb,
+                    ),
                     error_cb,
                 ),
-                SampleFormat::U16 => input.device.build_input_stream(
-                    &input.config,
-                    self.build_input_data_callback::<u16>(input_unparker, rb_producer),
+                SampleFormat::U16 => self.output.device.build_output_stream(
+                    &self.output.config,
+                    self.build_output_data_callback::<P, u16>(
+                        unparker,
+                        input_rb_consumer,
+                        midi_input_rb_consumer,
+                        midi_output_rb_producer.clone(),
+                        cb,
+                    ),
                     error_cb,
                 ),
-                SampleFormat::F32 => input.device.build_input_stream(
-                    &input.config,
-                    self.build_input_data_callback::<f32>(input_unparker, rb_producer),
+                SampleFormat::F32 => self.output.device.build_output_stream(
+                    &self.output.config,
+                    self.build_output_data_callback::<P, f32>(
+                        unparker,
+                        input_rb_consumer,
+                        midi_input_rb_consumer,
+                        midi_output_rb_producer.clone(),
+                        cb,
+                    ),
                     error_cb,
                 ),
             }
-            .expect("Fatal error creating the capture stream");
-            stream
+            .expect("Fatal error creating the output stream");
+
+            // TODO: Wait a period before doing this when also reading the input
+            output_stream
                 .play()
-                .expect("Fatal error trying to start the capture stream");
-            _input_stream = Some(stream);
+                .expect("Fatal error trying to start the output stream");
 
-            // Playback is delayed one period if we're capturing audio so it has something to process
-            input_parker.park()
-        }
+            // Wait for the audio thread to exit
+            parker.park();
 
-        // This thread needs to be blocked until audio processing ends as CPAL processes the streams
-        // on another thread instead of blocking
-        let parker = Parker::new();
-        let unparker = parker.unparker().clone();
-        let error_cb = {
-            let unparker = unparker.clone();
-            move |err| {
-                nih_error!("Error during playback: {err:#}");
-                unparker.clone().unpark();
-            }
-        };
+            // The Midir API requires us to take things out of Options and transform between these
+            // structs
+            *self.midi_input.lock() =
+                midi_input_connection.map(|midi_input_connection| MidirInputDevice {
+                    backend: midi_input_connection.connection.close().0,
+                    port: midi_input_connection.port,
+                });
+            *self.midi_output.lock() =
+                midi_output_connection.map(move |midi_output_connection_handle| {
+                    // The thread needs to be terminated first
+                    midi_output_rb_producer
+                        .expect("Inconsistent internal MIDI output state")
+                        .send(MidiOutputTask::Terminate)
+                        .expect("Could not terminate the MIDI output thread");
 
-        let output_stream = match self.output.sample_format {
-            SampleFormat::I16 => self.output.device.build_output_stream(
-                &self.output.config,
-                self.build_output_data_callback::<P, i16>(unparker, input_rb_consumer, cb),
-                error_cb,
-            ),
-            SampleFormat::U16 => self.output.device.build_output_stream(
-                &self.output.config,
-                self.build_output_data_callback::<P, u16>(unparker, input_rb_consumer, cb),
-                error_cb,
-            ),
-            SampleFormat::F32 => self.output.device.build_output_stream(
-                &self.output.config,
-                self.build_output_data_callback::<P, f32>(unparker, input_rb_consumer, cb),
-                error_cb,
-            ),
-        }
-        .expect("Fatal error creating the output stream");
+                    let midi_output_connection = midi_output_connection_handle
+                        .join()
+                        .expect("MIDI output thread panicked");
 
-        // TODO: Wait a period before doing this when also reading the input
-        output_stream
-            .play()
-            .expect("Fatal error trying to start the output stream");
-
-        // Wait for the audio thread to exit
-        parker.park();
+                    MidirOutputDevice {
+                        backend: midi_output_connection.connection.close(),
+                        port: midi_output_connection.port,
+                    }
+                });
+        });
     }
 }
 
@@ -351,10 +532,10 @@ impl CpalMidir {
                 };
 
                 match found_port {
-                    Some(port) => Some(Mutex::new(MidirInputDevice {
+                    Some(port) => Some(MidirInputDevice {
                         backend: midi_backend,
                         port: port.clone(),
-                    })),
+                    }),
                     None => {
                         let mut message = format!(
                             "Unknown input MIDI device '{midi_input_name}'. Available devices are:"
@@ -362,7 +543,7 @@ impl CpalMidir {
                         for port in available_ports {
                             match midi_backend.port_name(&port) {
                                 Ok(device_name) => message.push_str(&format!("\n{device_name}")),
-                                Err(err) => message.push_str(&format!("\nERROR: {err:?}")),
+                                Err(err) => message.push_str(&format!("\nERROR: {err:#}")),
                             }
                         }
 
@@ -388,10 +569,10 @@ impl CpalMidir {
                 };
 
                 match found_port {
-                    Some(port) => Some(Mutex::new(MidirOutputDevice {
+                    Some(port) => Some(MidirOutputDevice {
                         backend: midi_backend,
                         port: port.clone(),
-                    })),
+                    }),
                     None => {
                         let mut message = format!(
                             "Unknown output MIDI device '{midi_output_name}'. Available devices \
@@ -400,7 +581,7 @@ impl CpalMidir {
                         for port in available_ports {
                             match midi_backend.port_name(&port) {
                                 Ok(device_name) => message.push_str(&format!("\n{device_name}")),
-                                Err(err) => message.push_str(&format!("\nERROR: {err:?}")),
+                                Err(err) => message.push_str(&format!("\nERROR: {err:#}")),
                             }
                         }
 
@@ -418,8 +599,8 @@ impl CpalMidir {
             input,
             output,
 
-            midi_input,
-            midi_output,
+            midi_input: Mutex::new(midi_input),
+            midi_output: Mutex::new(midi_output),
         })
     }
 
@@ -443,10 +624,28 @@ impl CpalMidir {
         }
     }
 
+    fn build_midi_input_thread<P: Plugin>(
+        &self,
+        mut midi_input_rb_producer: rtrb::Producer<PluginNoteEvent<P>>,
+    ) -> impl FnMut(u64, &[u8], &mut ()) + Send + 'static {
+        // This callback parses the received MIDI bytes and sends them to a ring buffer
+        move |_timing, midi_data, _data| {
+            // Since this is system MIDI there's no real useful timing information and we'll set all
+            // the timings to the first sample in the buffer
+            if let Ok(event) = NoteEvent::from_midi(0, midi_data) {
+                if midi_input_rb_producer.push(event).is_err() {
+                    nih_error!("The MIDI input event queue was full, dropping event");
+                }
+            }
+        }
+    }
+
     fn build_output_data_callback<P: Plugin, T: Sample>(
         &self,
         unparker: Unparker,
         mut input_rb_consumer: Option<rtrb::Consumer<f32>>,
+        mut input_event_rb_consumer: Option<rtrb::Consumer<PluginNoteEvent<P>>>,
+        mut output_event_rb_producer: Option<crossbeam::channel::Sender<MidiOutputTask<P>>>,
         mut cb: impl FnMut(
                 &mut Buffer,
                 &mut AuxiliaryBuffers,
@@ -516,9 +715,8 @@ impl CpalMidir {
             aux_output_buffers.push(aux_buffer);
         }
 
-        // TODO: MIDI input and output
-        let midi_input_events = Vec::with_capacity(1024);
-        let mut midi_output_events = Vec::with_capacity(1024);
+        let mut midi_input_events = Vec::with_capacity(MIDI_EVENT_QUEUE_CAPACITY);
+        let mut midi_output_events = Vec::with_capacity(MIDI_EVENT_QUEUE_CAPACITY);
 
         // Can't borrow from `self` in the callback
         let config = self.config.clone();
@@ -615,6 +813,13 @@ impl CpalMidir {
                 }
             }
 
+            midi_input_events.clear();
+            if let Some(input_event_rb_consumer) = &mut input_event_rb_consumer {
+                if let Ok(event) = input_event_rb_consumer.pop() {
+                    midi_input_events.push(event);
+                }
+            }
+
             // SAFETY: Shortening these borrows is safe as even if the plugin overwrites the
             //         slices (which it cannot do without using unsafe code), then they
             //         would still be reset on the next iteration
@@ -647,7 +852,17 @@ impl CpalMidir {
                 *output_sample = T::from(buffer_sample);
             }
 
-            // TODO: Handle MIDI output events
+            if let Some(output_event_rb_producer) = &mut output_event_rb_producer {
+                for event in midi_output_events.drain(..) {
+                    if output_event_rb_producer
+                        .try_send(MidiOutputTask::Send(event))
+                        .is_err()
+                    {
+                        nih_error!("The MIDI output event queue was full, dropping event");
+                        break;
+                    }
+                }
+            }
 
             num_processed_samples += buffer.samples() as i64;
         }