fix a boundary case of Tail extra time

Case: when Tail's position becomes smaller than Head's

game.go

@@ -15,13 +15,6 @@ type Scene interface {
 	Draw(screen *ebiten.Image)
 }
 
-// func init() {
-// 	if runtime.GOOS == "windows" {
-// 		os.Setenv("EBITEN_GRAPHICS_LIBRARY", "opengl")
-// 		fmt.Println("OpenGL mode has enabled.")
-// 	}
-// }
-
 var (
 	modeProps     []ModeProp
 	sceneSelect   *SceneSelect

handler.go

@@ -148,8 +148,8 @@ func LoadHandlers(props []ModeProp) {
 
 	tailExtraTimeHandler = ctrl.FloatHandler{
 		Value: props[ModePiano4].Settings["TailExtraTime"],
-		Min:   -250,
-		Max:   250,
+		Min:   -200,
+		Max:   200,
 		Unit:  10,
 	}
 	TailExtraTimeKeyHandler = ctrl.KeyHandler{

mode/piano/chart.go

@@ -75,6 +75,11 @@ func NewChart(cpath string) (c *Chart, err error) {
 		n.Position = tp.Position + float64(n.Time-tp.Time)*tp.Speed
 		if n.Type == Tail {
 			n.Position += float64(TailExtraTime) * tp.Speed
+			// It is guaranteed that Tail's Prev (which is Head)
+			// has already proceeded, since c.Notes is sorted by Time.
+			if n.Position < n.Prev.Position {
+				n.Position = n.Prev.Position
+			}
 		}
 	}
 	tp = c.TransPoints[0]

mode/piano/drawer.go

@@ -118,12 +118,6 @@ func (d NoteDrawer) Draw(screen *ebiten.Image) {
 		}
 		sprite := d.Frame(d.Sprites[n.Type])
 		pos := n.Position - d.Cursor
-		// if n.Type == Tail {
-		// 	pos += BodyGain * SpeedScale
-		// 	if headPos := n.Prev.Position - d.Cursor; pos < headPos {
-		// 		pos = headPos
-		// 	}
-		// }
 		sprite.Move(0, -pos)
 		op := ebiten.DrawImageOptions{}
 		if n.Marked {