code: def _on_move(self, event):
          
          w = self.winfo_width()
          h = self.winfo_height()
          x = min(max(event.x, 0), w)
          y = min(max(event.y, 0), h)
          self.coords('cross_h', 0, y, w, y)
          self.coords('cross_v', x, 0, x, h)
          self.event_generate("<<ColorChanged>>")
docs: Make the cross follow the cursor.