如何在 Turtle 图形中实现多个按键组合以进行对角线移动？

在海龟图形中组合多个按键

在海龟图形中，可以实现注册多个按键来触发所需的操作。一个常见的示例是，当同时按下向上和向右箭头键时，让海龟沿对角线移动。

请考虑以下代码片段作为起点：

<code class="python">import turtle

flynn = turtle.Turtle()
win = turtle.Screen()
win.bgcolor("LightBlue")
flynn.pensize(7)
flynn.pencolor("lightBlue")

win.listen()

def Up():
    flynn.setheading(90)
    flynn.forward(25)

def Down():
    flynn.setheading(270)
    flynn.forward(20)

def Left():
    flynn.setheading(180)
    flynn.forward(20)

def Right():
    flynn.setheading(0)
    flynn.forward(20)

def upright():
    flynn.setheading(45)
    flynn.forward(20)

win.onkey(Up, "Up")
win.onkey(Down,"Down")
win.onkey(Left,"Left")
win.onkey(Right,"Right")</code>

虽然此代码允许您执行单独的按键操作，它不适合同时按下按键进行对角移动。

另一种方法

另一种方法是采用排队事件系统。按键事件不是在按键时直接执行操作，而是存储在队列中。然后，计时器定期检查队列并执行排队的操作。这种方法允许捕获和组合多个按键。

以下代码演示了这种替代方法：

<code class="python">from turtle import Turtle, Screen

win = Screen()

flynn = Turtle('turtle')

def process_events():
    events = tuple(sorted(key_events))

    if events and events in key_event_handlers:
        (key_event_handlers[events])()

    key_events.clear()

    win.ontimer(process_events, 200)

def Up():
    key_events.add('UP')

def Down():
    key_events.add('DOWN')

def Left():
    key_events.add('LEFT')

def Right():
    key_events.add('RIGHT')

def move_up():
    flynn.setheading(90)
    flynn.forward(25)

def move_down():
    flynn.setheading(270)
    flynn.forward(20)

def move_left():
    flynn.setheading(180)
    flynn.forward(20)

def move_right():
    flynn.setheading(0)
    flynn.forward(20)

def move_up_right():
    flynn.setheading(45)
    flynn.forward(20)

def move_down_right():
    flynn.setheading(-45)
    flynn.forward(20)

def move_up_left():
    flynn.setheading(135)
    flynn.forward(20)

def move_down_left():
    flynn.setheading(225)
    flynn.forward(20)

key_event_handlers = { \
    ('UP',): move_up, \
    ('DOWN',): move_down, \
    ('LEFT',): move_left, \
    ('RIGHT',): move_right, \
    ('RIGHT', 'UP'): move_up_right, \
    ('DOWN', 'RIGHT'): move_down_right, \
    ('LEFT', 'UP'): move_up_left, \
    ('DOWN', 'LEFT'): move_down_left, \
}

key_events = set()

win.onkey(Up, "Up")
win.onkey(Down, "Down")
win.onkey(Left, "Left")
win.onkey(Right, "Right")

win.listen()

process_events()

win.mainloop()</code>

使用这种方法，当同时按下向上和向右箭头键时，move_up_right函数被触发，导致海龟沿对角线方向移动。

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