feat(tracker): implement selecting a range in the tracker

also refactored a location in song to SongPoint, and a particular row in song into SongRow

tracker/songpoint.go

@@ -0,0 +1,85 @@
+package tracker
+
+import "github.com/vsariola/sointu"
+
+type SongRow struct {
+	Pattern int
+	Row     int
+}
+
+type SongPoint struct {
+	Track int
+	SongRow
+}
+
+type SongRect struct {
+	Corner1 SongPoint
+	Corner2 SongPoint
+}
+
+func (r *SongRow) Wrap(song sointu.Song) {
+	totalRow := r.Pattern*song.PatternRows() + r.Row
+	r.Row = mod(totalRow, song.PatternRows())
+	r.Pattern = mod((totalRow-r.Row)/song.PatternRows(), song.SequenceLength())
+}
+
+func (r *SongRow) Clamp(song sointu.Song) {
+	totalRow := r.Pattern*song.PatternRows() + r.Row
+	if totalRow < 0 {
+		totalRow = 0
+	}
+	if totalRow >= song.TotalRows() {
+		totalRow = song.TotalRows() - 1
+	}
+	r.Row = totalRow % song.PatternRows()
+	r.Pattern = ((totalRow - r.Row) / song.PatternRows()) % song.SequenceLength()
+}
+
+func (p *SongPoint) Wrap(song sointu.Song) {
+	p.Track = mod(p.Track, len(song.Tracks))
+	p.SongRow.Wrap(song)
+}
+
+func (p *SongPoint) Clamp(song sointu.Song) {
+	if p.Track < 0 {
+		p.Track = 0
+	} else if l := len(song.Tracks); p.Track >= l {
+		p.Track = l - 1
+	}
+	p.SongRow.Clamp(song)
+}
+
+func (r *SongRect) Contains(p SongPoint) bool {
+	track1, track2 := r.Corner1.Track, r.Corner2.Track
+	if track2 < track1 {
+		track1, track2 = track2, track1
+	}
+	if p.Track < track1 || p.Track > track2 {
+		return false
+	}
+	pattern1, row1, pattern2, row2 := r.Corner1.Pattern, r.Corner1.Row, r.Corner2.Pattern, r.Corner2.Row
+	if pattern2 < pattern1 || (pattern1 == pattern2 && row2 < row1) {
+		pattern1, row1, pattern2, row2 = pattern2, row2, pattern1, row1
+	}
+	if p.Pattern < pattern1 || p.Pattern > pattern2 {
+		return false
+	}
+	if p.Pattern == pattern1 && p.Row < row1 {
+		return false
+	}
+	if p.Pattern == pattern2 && p.Row > row2 {
+		return false
+	}
+	return true
+}
+
+func mod(a, b int) int {
+	m := a % b
+	if a < 0 && b < 0 {
+		m -= b
+	}
+	if a < 0 && b > 0 {
+		m += b
+	}
+	return m
+}