feat(tracker): add a rudimentary VU-meter to show master volume, peaks & clipping

Closes #16

tracker/sequencer.go

@@ -47,7 +47,7 @@ type noteID struct {
 	id    uint32
 }
 
-func NewSequencer(bufferSize int, service sointu.SynthService, context sointu.AudioContext, iterator func([]RowNote) []RowNote) *Sequencer {
+func NewSequencer(bufferSize int, service sointu.SynthService, context sointu.AudioContext, callBack func([]float32), iterator func([]RowNote) []RowNote) *Sequencer {
 	ret := &Sequencer{
 		closer:        make(chan struct{}),
 		setPatch:      make(chan sointu.Patch, 32),
@@ -60,11 +60,11 @@ func NewSequencer(bufferSize int, service sointu.SynthService, context sointu.Au
 	// the iterator is a bit unconventional in the sense that it might return
 	// false to indicate that there is no row available, but might still return
 	// true in future attempts if new rows become available.
-	go ret.loop(bufferSize, service, context, iterator)
+	go ret.loop(bufferSize, service, context, callBack, iterator)
 	return ret
 }
 
-func (s *Sequencer) loop(bufferSize int, service sointu.SynthService, context sointu.AudioContext, iterator func([]RowNote) []RowNote) {
+func (s *Sequencer) loop(bufferSize int, service sointu.SynthService, context sointu.AudioContext, callBack func([]float32), iterator func([]RowNote) []RowNote) {
 	buffer := make([]float32, bufferSize)
 	renderTries := 0
 	audioOut := context.Output()
@@ -141,6 +141,7 @@ func (s *Sequencer) loop(bufferSize int, service sointu.SynthService, context so
 					}
 				}
 				rendered, timeAdvanced, err := s.synth.Render(buffer, renderTime)
+				callBack(buffer)
 				if err != nil {
 					s.Disable()
 					break

tracker/songpanel.go

@@ -192,5 +192,6 @@ func (t *Tracker) layoutSongOptions(gtx C) D {
 			gtx.Constraints.Min = image.Pt(0, 0)
 			return panicBtnStyle.Layout(gtx)
 		}),
+		layout.Rigid(t.VuMeter.Layout),
 	)
 }

tracker/tracker.go

@@ -71,6 +71,7 @@ type Tracker struct {
 	InstrumentDragList    *DragList
 	TrackHexCheckBoxes    []*widget.Bool
 	TrackShowHex          []bool
+	VuMeter               VuMeter
 	TopHorizontalSplit    *Split
 	BottomHorizontalSplit *Split
 	VerticalSplit         *Split
@@ -695,10 +696,23 @@ func New(audioContext sointu.AudioContext, synthService sointu.SynthService) *Tr
 	t.TopHorizontalSplit.Ratio = -.6
 	t.Theme.Palette.Fg = primaryColor
 	t.Theme.Palette.ContrastFg = black
+	t.EditMode = EditTracks
+	t.Step.Value = 1
+	t.VuMeter.FallOff = 2e-8
+	t.VuMeter.RangeDb = 80
+	t.VuMeter.Decay = 1e-3
 	for range allUnits {
 		t.ChooseUnitTypeBtns = append(t.ChooseUnitTypeBtns, new(widget.Clickable))
 	}
-	t.sequencer = NewSequencer(2048, synthService, audioContext, func(row []RowNote) []RowNote {
+	callBack := func(buf []float32) {
+		t.VuMeter.Update(buf)
+		select {
+		case t.refresh <- struct{}{}:
+		default:
+			// message dropped, there's already a tick queued, so no need to queue extra
+		}
+	}
+	t.sequencer = NewSequencer(2048, synthService, audioContext, callBack, func(row []RowNote) []RowNote {
 		t.playRowPatMutex.Lock()
 		if !t.Playing {
 			t.playRowPatMutex.Unlock()

tracker/vumeter.go

@@ -0,0 +1,78 @@
+package tracker
+
+import (
+	"image"
+	"math"
+
+	"gioui.org/f32"
+	"gioui.org/op"
+	"gioui.org/op/clip"
+	"gioui.org/op/paint"
+	"gioui.org/unit"
+)
+
+type VuMeter struct {
+	avg     [2]float32
+	max     [2]float32
+	speed   [2]float32
+	FallOff float32
+	Decay   float32
+	RangeDb float32
+}
+
+func (v *VuMeter) Update(buffer []float32) {
+	for j := 0; j < 2; j++ {
+		for i := 0; i < len(buffer); i += 2 {
+			sample2 := buffer[i+j] * buffer[i+j]
+			db := float32(10*math.Log10(float64(sample2))) + v.RangeDb
+			v.speed[j] += v.FallOff
+			v.max[j] -= v.speed[j]
+			if v.max[j] < 0 {
+				v.max[j] = 0
+			}
+			if v.max[j] < db {
+				v.max[j] = db
+				v.speed[j] = 0
+			}
+			v.avg[j] += (sample2 - v.avg[j]) * v.Decay
+			if math.IsNaN(float64(v.avg[j])) {
+				v.avg[j] = 0
+			}
+		}
+	}
+}
+
+func (v *VuMeter) Reset() {
+	v.avg = [2]float32{}
+	v.max = [2]float32{}
+}
+
+func (v *VuMeter) Layout(gtx C) D {
+	defer op.Save(gtx.Ops).Load()
+	gtx.Constraints.Max.Y = gtx.Px(unit.Dp(12))
+	height := gtx.Px(unit.Dp(6))
+	for j := 0; j < 2; j++ {
+		value := float32(10*math.Log10(float64(v.avg[j]))) + v.RangeDb
+		if value > 0 {
+			x := int(value/v.RangeDb*float32(gtx.Constraints.Max.X) + 0.5)
+			if x > gtx.Constraints.Max.X {
+				x = gtx.Constraints.Max.X
+			}
+			paint.FillShape(gtx.Ops, mediumEmphasisTextColor, clip.Rect(image.Rect(0, 0, x, height)).Op())
+		}
+		valueMax := v.max[j]
+		if valueMax > 0 {
+			color := white
+			if valueMax >= v.RangeDb {
+				color = errorColor
+			}
+			x := int(valueMax/v.RangeDb*float32(gtx.Constraints.Max.X) + 0.5)
+			if x > gtx.Constraints.Max.X {
+				x = gtx.Constraints.Max.X
+			}
+			paint.FillShape(gtx.Ops, color, clip.Rect(image.Rect(x-1, 0, x, height)).Op())
+		}
+		op.Offset(f32.Pt(0, float32(height))).Add(gtx.Ops)
+	}
+	return D{Size: gtx.Constraints.Max}
+}