feat(tracker): implement basic track display

go4k/tracker/tracker.go

@@ -1,13 +1,22 @@
 package tracker
 
-import "gioui.org/widget"
+import (
+	"gioui.org/widget"
+	"github.com/vsariola/sointu/go4k"
+)
 
 type Tracker struct {
-	QuitButton *widget.Clickable
+	QuitButton     *widget.Clickable
+	song           go4k.Song
+	CursorRow      int
+	CursorColumn   int
+	DisplayPattern int
+	ActiveTrack    int
 }
 
 func New() *Tracker {
 	return &Tracker{
 		QuitButton: new(widget.Clickable),
+		song:       defaultSong,
 	}
 }