feat(tracker): hook up audio to tracker, we have liftoff

audio still a bit crackly; should probably decouple actual row ticking and rendering of audio (but how does that work with tempo ops?)

sequencer goroutine is a bit weird, too, should rethink

go4k/tracker/sequencer.go

@@ -0,0 +1,87 @@
+package tracker
+
+import (
+	"fmt"
+	"sync/atomic"
+	"time"
+)
+
+func (t *Tracker) TogglePlay() {
+	t.Playing = !t.Playing
+	t.setPlaying <- t.Playing
+}
+
+// sequencerLoop is the main goroutine that handles the playing logic
+func (t *Tracker) sequencerLoop() {
+	playing := false
+	rowTime := (time.Second * 60) / time.Duration(4*t.song.BPM)
+	tick := make(<-chan time.Time)
+	curVoices := make([]int, len(t.song.Tracks))
+	for i := range curVoices {
+		curVoices[i] = t.song.FirstTrackVoice(i)
+	}
+	for {
+		select {
+		case <-tick:
+			next := time.Now().Add(rowTime)
+			pattern := atomic.LoadInt32(&t.PlayPattern)
+			row := atomic.LoadInt32(&t.PlayRow)
+			if int(row+1) == t.song.PatternRows() {
+				if int(pattern+1) == t.song.SequenceLength() {
+					atomic.StoreInt32(&t.PlayPattern, 0)
+				} else {
+					atomic.AddInt32(&t.PlayPattern, 1)
+				}
+				atomic.StoreInt32(&t.PlayRow, 0)
+			} else {
+				atomic.AddInt32(&t.PlayRow, 1)
+			}
+			if playing {
+				tick = time.After(next.Sub(time.Now()))
+			}
+			t.playRow(curVoices)
+			t.ticked <- struct{}{}
+		// TODO: maybe refactor the controls to be nicer, somehow?
+		case rowJump := <-t.rowJump:
+			atomic.StoreInt32(&t.PlayRow, int32(rowJump))
+		case patternJump := <-t.patternJump:
+			atomic.StoreInt32(&t.PlayPattern, int32(patternJump))
+		case playState := <-t.setPlaying:
+			playing = playState
+			if playing {
+				t.playBuffer = make([]float32, t.song.SamplesPerRow())
+				tick = time.After(0)
+			}
+		}
+	}
+}
+
+// playRow renders and writes the current row
+func (t *Tracker) playRow(curVoices []int) {
+	pattern := atomic.LoadInt32(&t.PlayPattern)
+	row := atomic.LoadInt32(&t.PlayRow)
+	for i, trk := range t.song.Tracks {
+		patternIndex := trk.Sequence[pattern]
+		note := t.song.Patterns[patternIndex][row]
+		if note == 1 { // anything but hold causes an action.
+			continue // TODO: can hold be actually something else than 1?
+		}
+		t.synth.Release(curVoices[i])
+		if note > 1 {
+			curVoices[i]++
+			first := t.song.FirstTrackVoice(i)
+			if curVoices[i] >= first+trk.NumVoices {
+				curVoices[i] = first
+			}
+			t.synth.Trigger(curVoices[i], note)
+		}
+	}
+	buff := make([]float32, t.song.SamplesPerRow()*2)
+	rendered, timeAdvanced, _ := t.synth.Render(buff, t.song.SamplesPerRow())
+	err := t.player.Play(buff)
+	if err != nil {
+		fmt.Println("error playing: %w", err)
+	} else if timeAdvanced != t.song.SamplesPerRow() {
+		fmt.Println("rendered only", rendered, "/", timeAdvanced, "expected", t.song.SamplesPerRow())
+	}
+}