now 'all' the file are in order

Script/ball.gd

@@ -0,0 +1,20 @@
+extends StaticBody3D
+signal entrato 
+signal uscito
+
+# Called when the node enters the scene tree for the first time.
+func _ready() -> void:
+	pass # Replace with function body.
+
+
+# Called every frame. 'delta' is the elapsed time since the previous frame.
+func _process(delta: float) -> void:
+	pass
+
+# se e "visibile nello schermo" emit ma emit anche se ce un muro davanti
+func _on_visible_on_screen_notifier_3d_screen_entered() -> void:
+	entrato.emit()
+
+
+func _on_visible_on_screen_notifier_3d_screen_exited() -> void:
+	uscito.emit()

Script/ball.gd.uid

@@ -0,0 +1 @@
+uid://br3i356g3fo3f