text: #!/usr/bin/python3
  # -*- coding: utf-8 -*-
  
  from projectile import Projectile
  from graphics import Circle, Point
  
  class ShotTracker(object):
  	def __init__(self, win, angle, velocity, height):
  		self.proj = Projectile(angle, velocity, height)
  		self.marker = Circle(Point(0, height), 3)	# 圆心, 半径
  		self.marker.setFill('red')
  		self.marker.setOutline('red')
  		self.marker.draw(win)
  
  	def update(self, dt):
  		self.proj.update(dt)
  
  		center = self.marker.getCenter()
  		dx = self.proj.getX() - center.getX()
  		dy = self.proj.getY() - center.getY()
  		self.marker.move(dx, dy)
  
  	def getX(self):
  		return self.proj.getX()
  
  	def getY(self):
  		return self.proj.getY()
  
  	def undraw(self):
  		self.marker.undraw()
  