Play sfx in a loop

audio/audio.go

@@ -19,7 +19,9 @@ package audio
 //
 // offset is the note position to start playing (0-31). Offset is clamped to [0,31].
 //
-// length is the number of notes to play (1-32). Length <= 0 is automatically updated to 32.
+// length is the number of notes to play. If length <= 0 and sfx has no loop
+// then entire sfx is played. If length < sfx length then only fraction of sfx is
+// played. If length <= 0 and sfx has loop then sfx is played infinitely.
 func Sfx(sfxNo int, channel Channel, offset, length int) {
 	system.Sfx(sfxNo, channel, offset, length)
 }
@@ -118,6 +120,14 @@ type SoundEffect struct {
 	Buzz      bool
 }
 
+func (s SoundEffect) noteAt(no int) Note {
+	var note Note
+	if no < len(s.Notes) {
+		note = s.Notes[no]
+	}
+	return note
+}
+
 type Note struct {
 	Pitch      Pitch      // 0-63
 	Instrument Instrument // 0-15

audio/synth.go

@@ -59,7 +59,7 @@ func (c *channel) readSample(sfx SoundEffect) float64 {
 
 	var sample float64
 
-	volume := float64(sfx.Notes[c.noteNo].Volume) / 7
+	volume := float64(sfx.noteAt(c.noteNo).Volume) / 7
 	sample = c.oscillator.NextSample() * volume
 
 	c.sampleNo += 1
@@ -72,16 +72,25 @@ func (c *channel) readSample(sfx SoundEffect) float64 {
 }
 
 func (c *channel) moveToNextNote(sfx SoundEffect) {
+	c.notesToGo--
 	c.noteNo++
 
-	if c.noteNo == c.lastNoteNo {
+	if c.noteNo == int(sfx.LoopStop) {
+		c.noteNo = int(sfx.LoopStart)
+	}
+
+	maxLenReached := sfx.LoopStop == 0 && int(sfx.LoopStart) == c.noteNo
+	hasLoop := sfx.LoopStop > 0 // TODO  sfx.LoopStart must be != sfx.LoopStop
+	infiniteLoop := hasLoop && c.infiniteLoop
+	if (c.notesToGo == 0 && !infiniteLoop) || maxLenReached {
 		c.playing = false
 		return
 	}
 
 	c.noteEndSample += singleNoteSamples(sfx.Speed)
 
-	note := sfx.Notes[c.noteNo]
+	note := sfx.noteAt(c.noteNo)
+
 	c.oscillator.Func = oscillatorFunc(note.Instrument)
 	c.oscillator.FreqHz = pitchToFreq(note.Pitch)
 }
@@ -102,6 +111,7 @@ func (s *Synthesizer) Sfx(sfxNo int, ch Channel, offset, length int) {
 
 	if length <= 0 {
 		length = 32
+		s.channels[ch].infiniteLoop = true
 	}
 
 	s.channels[ch].playing = true
@@ -110,7 +120,7 @@ func (s *Synthesizer) Sfx(sfxNo int, ch Channel, offset, length int) {
 
 	s.channels[ch].sampleNo = 0
 	s.channels[ch].noteNo = offset
-	s.channels[ch].lastNoteNo = length
+	s.channels[ch].notesToGo = length
 
 	s.channels[ch].noteEndSample = singleNoteSamples(sfx.Speed)
 
@@ -325,7 +335,8 @@ func boolToByte(b bool) byte {
 type channel struct {
 	sfxNo         int
 	noteNo        int
-	lastNoteNo    int
+	notesToGo     int
+	infiniteLoop  bool
 	sampleNo      int
 	noteEndSample int
 	oscillator    internal.Oscillator