feat(tracker): add support for a MIDI controller to the standalone tracker

Closes #132.

tracker/gomidi/midi.go

@@ -0,0 +1,115 @@
+package gomidi
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/vsariola/sointu/tracker"
+	"gitlab.com/gomidi/midi/v2"
+	"gitlab.com/gomidi/midi/v2/drivers"
+	"gitlab.com/gomidi/midi/v2/drivers/rtmididrv"
+)
+
+type (
+	MIDIContext struct {
+		driver          *rtmididrv.Driver
+		inputAvailable  bool
+		driverAvailable bool
+		currentIn       MIDIDevicer
+		events          chan midi.Message
+	}
+	MIDIDevicer drivers.In
+)
+
+func (m *MIDIContext) ListInputDevices() <-chan tracker.MIDIDevicer {
+
+	ins, err := m.driver.Ins()
+	channel := make(chan tracker.MIDIDevicer, len(ins))
+	if err != nil {
+		m.driver.Close()
+		m.driverAvailable = false
+		return nil
+	}
+	go func() {
+		for i := 0; i < len(ins); i++ {
+			channel <- ins[i].(MIDIDevicer)
+		}
+		close(channel)
+	}()
+	return channel
+}
+
+// Open the driver.
+func CreateContext() *MIDIContext {
+	m := MIDIContext{}
+	var err error
+	m.driver, err = rtmididrv.New()
+	m.driverAvailable = err == nil
+	if m.driverAvailable {
+		m.events = make(chan midi.Message)
+	}
+	return &m
+}
+
+// Open an input device while closing the currently open if necessary.
+func (m *MIDIContext) OpenInputDevice(in tracker.MIDIDevicer) bool {
+	fmt.Printf("Opening midi device %s\n.", in)
+	if m.driverAvailable {
+		if m.currentIn == in {
+			return false
+		}
+		if m.inputAvailable && m.currentIn.IsOpen() {
+			m.currentIn.Close()
+		}
+		m.currentIn = in.(MIDIDevicer)
+		m.currentIn.Open()
+		_, err := midi.ListenTo(m.currentIn, m.HandleMessage)
+		if err != nil {
+			m.inputAvailable = false
+			return false
+		}
+	}
+	return true
+}
+
+func (m *MIDIContext) HandleMessage(msg midi.Message, timestampms int32) {
+	go func() {
+		m.events <- msg
+		time.Sleep(time.Nanosecond)
+	}()
+}
+
+func (c *MIDIContext) NextEvent() (event tracker.MIDINoteEvent, ok bool) {
+	select {
+	case msg := <-c.events:
+		{
+			var channel uint8
+			var velocity uint8
+			var key uint8
+			var controller uint8
+			var value uint8
+			if msg.GetNoteOn(&channel, &key, &velocity) {
+				return tracker.MIDINoteEvent{Frame: 0, On: true, Channel: int(channel), Note: key}, true
+			} else if msg.GetNoteOff(&channel, &key, &velocity) {
+				return tracker.MIDINoteEvent{Frame: 0, On: false, Channel: int(channel), Note: key}, true
+			} else if msg.GetControlChange(&channel, &controller, &value) {
+				fmt.Printf("CC @ Channel: %d, Controller: %d, Value: %d\n", channel, controller, value)
+			} else {
+				fmt.Printf("Unhandled MIDI message: %s\n", msg)
+			}
+		}
+	default:
+		// Note (@LeStahL): This empty select case is needed to make the implementation non-blocking.
+	}
+	return tracker.MIDINoteEvent{}, false
+}
+
+func (c *MIDIContext) BPM() (bpm float64, ok bool) {
+	return 0, false
+}
+
+func (c *MIDIContext) DestroyContext() {
+	close(c.events)
+	c.currentIn.Close()
+	c.driver.Close()
+}