在海龜圖形中組合多個按鍵

在海龜圖形中，可以實現(xiàn)註冊多個按鍵來觸發(fā)所需的操作。一個常見的例子是，當(dāng)同時按下向上和向右箭頭鍵時，讓海龜沿著對角線移動。

請考慮以下程式碼片段作為起點：

<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>

雖然此程式碼允許您執(zhí)行單獨的按鍵操作，它不適合同時按下按鍵進行對角線移動。

另一種方法

另一種方法是採用排隊事件系統(tǒng)。按鍵事件不是在按鍵時直接執(zhí)行操作，而是儲存在佇列中。然後，計時器會定期檢查佇列並執(zhí)行排隊的操作。這種方法允許捕獲和組合多個按鍵。

以下程式碼示範(fàn)了這個替代方法：

<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>

使用這種方法，當(dāng)同時按下向上和向右箭頭鍵時，move_up_right函數(shù)被觸發(fā)，導(dǎo)致海龜沿對角線方向移動。

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