在Python編程中，使用畫布進行圖形繪制是很常見的。但是當繪制的圖形比較大或者需要進行拖動時，就需要實現畫布的拖動功能。下面介紹一種實現畫布拖動的方法。

from tkinter import *
class MoveableCanvas(Canvas):
def __init__(self, master=None, **kw):
Canvas.__init__(self, master=master, **kw)
self.bind("", self.on_button_press)
self.bind("", self.on_move_press)
self.bind("", self.on_zoom)
self.bind("", self.on_zoom)
self.bind("", self.on_zoom)
self.bind("", self.on_resize)
self.rect = None
self.start_x = None
self.start_y = None
def on_button_press(self, event):
self.start_x = self.canvasx(event.x)
self.start_y = self.canvasy(event.y)
self.rect = self.create_rectangle(
self.start_x, self.start_y, self.start_x, self.start_y
)
def on_move_press(self, event):
cur_x = self.canvasx(event.x)
cur_y = self.canvasy(event.y)
if self.rect:
self.coords(self.rect, self.start_x, self.start_y, cur_x, cur_y)
dx = cur_x - self.start_x
dy = cur_y - self.start_y
self.scan_mark(0, 0)
self.scan_dragto(dx, dy, gain=1)
def on_zoom(self, event):
if event.delta >0:
self.scale("all", event.x, event.y, 1.1, 1.1)
elif event.delta< 0:
self.scale("all", event.x, event.y, 0.9, 0.9)
def on_resize(self, event):
self.scan_mark(0, 0)
self.scan_dragto(event.width, event.height, gain=1)
root = Tk()
canvas = MoveableCanvas(root, width=800, height=600, bg="white")
canvas.pack(fill=BOTH, expand=YES)
for i in range(400):
for j in range(300):
canvas.create_oval(i*5, j*5, i*5+5, j*5+5, fill="blue", outline="blue")
root.mainloop()

上述代碼中，定義了一個繼承自Canvas的MoveableCanvas類。在該類中重寫了鼠標按下、拖動、滾輪、調整畫布大小等事件的方法。通過在畫布上創建一個矩形，實現拖動畫布。使用scale方法實現畫布的縮放。