如何让一只乌龟在另一只乌龟上方绘制？

Question

我正在做一个项目，其中有一只乌龟画了一条黑线，但紧随其后的是另一只乌龟画了一条白线。我想让这条白线画在黑线上以“擦除”黑线，但黑线仍然在白线上方。

我正在 trinket.io

上编程

这是我的代码：

import turtle 

#create elements
pen = turtle.Turtle()
follow = turtle.Turtle()
screen = turtle.Screen()


#create variables
positions = [0,-180,0,-180,0,-180,0,-180,0,-180,0,-180,0,-180,0,-180,0,-180,0,-180]


#moving functions
def move_left():
  if pen.xcor() > -180:
    pen.goto(pen.xcor()-10,pen.ycor())
def move_right():
  if pen.xcor() < 180:
    pen.goto(pen.xcor()+10,pen.ycor())
def move_up():
  if pen.ycor() < 180:
    pen.goto(pen.xcor(),pen.ycor()+10)
def move_down():
  if pen.ycor() > -180:
    pen.goto(pen.xcor(),pen.ycor()-10)


#pen setup
pen.speed(1000)
pen.penup()
pen.goto(0,-180)
pen.left(90)
pen.pendown()

follow.left(90)
follow.color("#FFFFF1")
follow.width(50)


#adjust frame refresh settings
pen.tracer(0,0)
rate = 0
refresh = 0


#game functionality
def game():
  screen.onkey(move_left, 'left')
  screen.onkey(move_right, 'right')
  screen.onkey(move_up, 'up')
  screen.onkey(move_down, 'down')
  follow.goto(positions[0],positions[1])
  positions.append(pen.xcor())
  positions.append(pen.ycor())
  positions.pop(0)
  positions.pop(0)


#wait for keys
screen.listen()


#loop
while True:
  game()
  if refresh < rate:
    refresh = refresh + 1
  else:
    pen.update()
    #print(positions)
    refresh = 0

如何修复我的程序？

Answer 1

您只需调用每个 screen.onkey() 实例一次，在循环中（间接）调用它们不会获得任何好处。此外，不清楚为什么 positions 被预初始化为十个位置。

我猜你想要一只留下踪迹的乌龟，但那条踪迹的长度有限，随着新踪迹的铺设，它的尽头会消失。根据您的描述，您希望它在 trinket.io 乌龟中工作，这意味着我们不能使用像 stamps 这样的功能来使它更清洁。

下面是我对您的代码进行的修改，我已经在 trinket.io 上进行了测试，它留下了 20 个线段。最旧的线段随着新线段的放置而消失：

from turtle import Screen, Turtle

NUMBER_SEGMENTS = 20

# moving functions
def truncate():
    if len(positions) >= NUMBER_SEGMENTS:
        follower.setposition(positions.pop(0))

    screen.update()

def move_left():
    pen.setheading(180)

    if pen.xcor() > -180:
        pen.forward(10)
        positions.append(pen.position())

    truncate()

def move_right():
    pen.setheading(0)

    if pen.xcor() < 180:
        pen.forward(10)
        positions.append(pen.position())

    truncate()

def move_up():
    pen.setheading(90)

    if pen.ycor() < 180:
        pen.forward(10)
        positions.append(pen.position())

    truncate()

def move_down():
    pen.setheading(270)

    if pen.ycor() > -180:
        pen.forward(10)
        positions.append(pen.position())

    truncate()

# create elements
screen = Screen()

# adjust frame refresh settings
screen.tracer(0)

refresh = 0

# pen setup
pen = Turtle()
pen.speed('fastest')
pen.penup()
pen.sety(-180)
pen.setheading(90)
pen.pendown()

follower = pen.clone()
follower.hideturtle()
follower.width(3)
follower.color('#F9F9F9')

# create variables
positions = []

# wait for keys
screen.onkey(move_left, 'Left')
screen.onkey(move_right, 'Right')
screen.onkey(move_up, 'Up')
screen.onkey(move_down, 'Down')
screen.listen()
screen.update()
screen.mainloop()

不完美，但是trinket.io有点束缚我们的爪子。这大致就是您要尝试做的事情吗？

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