feat(tracker, gioui): add ability & button to delete tracks.

Refer #46.

tracker/gioui/track.go

@@ -32,6 +32,10 @@ func (t *Tracker) layoutTracker(gtx layout.Context) layout.Dimensions {
 		t.AddTrack(true)
 	}
 
+	for t.DeleteTrackBtn.Clicked() {
+		t.DeleteTrack(false)
+	}
+
 	//t.TrackHexCheckBoxes[i2].Value = t.TrackShowHex[i2]
 	//cbStyle := material.CheckBox(t.Theme, t.TrackHexCheckBoxes[i2], "hex")
 	//cbStyle.Color = white
@@ -70,6 +74,14 @@ func (t *Tracker) layoutTracker(gtx layout.Context) layout.Dimensions {
 		subtractOctaveBtnStyle.Color = primaryColor
 		subtractOctaveBtnStyle.Background = transparent
 		subtractOctaveBtnStyle.Inset = layout.UniformInset(unit.Dp(6))
+		deleteTrackBtnStyle := material.IconButton(t.Theme, t.DeleteTrackBtn, widgetForIcon(icons.ActionDelete))
+		deleteTrackBtnStyle.Background = transparent
+		deleteTrackBtnStyle.Inset = layout.UniformInset(unit.Dp(6))
+		if t.CanDeleteTrack() {
+			deleteTrackBtnStyle.Color = primaryColor
+		} else {
+			deleteTrackBtnStyle.Color = disabledTextColor
+		}
 		newTrackBtnStyle := material.IconButton(t.Theme, t.NewTrackBtn, widgetForIcon(icons.ContentAdd))
 		newTrackBtnStyle.Background = transparent
 		newTrackBtnStyle.Inset = layout.UniformInset(unit.Dp(6))
@@ -110,6 +122,7 @@ func (t *Tracker) layoutTracker(gtx layout.Context) layout.Dimensions {
 			layout.Rigid(Label("  Voices:", white)),
 			layout.Rigid(voiceUpDown),
 			layout.Flexed(1, func(gtx C) D { return layout.Dimensions{Size: gtx.Constraints.Min} }),
+			layout.Rigid(deleteTrackBtnStyle.Layout),
 			layout.Rigid(newTrackBtnStyle.Layout))
 		t.Song().Score.Tracks[t.Cursor().Track].Effect = t.TrackHexCheckBox.Value // TODO: we should not modify the model, but how should this be done
 		t.SetTrackVoices(t.TrackVoices.Value)

tracker/gioui/tracker.go

@@ -28,6 +28,7 @@ type Tracker struct {
 	TrackVoices           *NumberInput
 	InstrumentNameEditor  *widget.Editor
 	NewTrackBtn           *widget.Clickable
+	DeleteTrackBtn        *widget.Clickable
 	NewInstrumentBtn      *widget.Clickable
 	DeleteInstrumentBtn   *widget.Clickable
 	AddSemitoneBtn        *widget.Clickable
@@ -113,6 +114,7 @@ func New(audioContext sointu.AudioContext, synthService sointu.SynthService, syn
 		TrackVoices:           new(NumberInput),
 		InstrumentNameEditor:  &widget.Editor{SingleLine: true, Submit: true, Alignment: text.Middle},
 		NewTrackBtn:           new(widget.Clickable),
+		DeleteTrackBtn:        new(widget.Clickable),
 		NewInstrumentBtn:      new(widget.Clickable),
 		DeleteInstrumentBtn:   new(widget.Clickable),
 		AddSemitoneBtn:        new(widget.Clickable),

tracker/model.go

@@ -203,6 +203,27 @@ func (m *Model) CanAddTrack() bool {
 	return m.song.Score.NumVoices() < 32
 }
 
+func (m *Model) DeleteTrack(forward bool) {
+	if !m.CanDeleteTrack() {
+		return
+	}
+	m.saveUndo("DeleteTrack", 0)
+	newTracks := make([]sointu.Track, len(m.song.Score.Tracks)-1)
+	copy(newTracks, m.song.Score.Tracks[:m.cursor.Track])
+	copy(newTracks[m.cursor.Track:], m.song.Score.Tracks[m.cursor.Track+1:])
+	m.song.Score.Tracks = newTracks
+	if !forward {
+		m.cursor.Track--
+	}
+	m.selectionCorner = m.cursor
+	m.clampPositions()
+	m.notifyScoreChange()
+}
+
+func (m *Model) CanDeleteTrack() bool {
+	return len(m.song.Score.Tracks) > 1
+}
+
 func (m *Model) SetTrackVoices(value int) {
 	if value < 1 {
 		value = 1