python opencv 简单绘制画板

import  cv2
import  numpy as np

#基本功能:
# 可以通过鼠标进行基本图形的绘制
#1.可以画线: 当用户按下1键，即选择了画线。此时，滑动鼠标即可画线。
#2.可以画矩形:当用户按下r键，即可选择画矩形。此时，滑动鼠标即可画矩形。
#3.可以画圆:当用户按下c键，即可选择画圆。此时，滑动鼠标即可画圆。
curshape = 0 # 0 画线 1 画矩形 2 画圆
startpos = (0,0)
img = np.zeros((480,640,3),np.uint8)

# 鼠标回调函数
def mouse_callback(event,x,y,flags,param):
    global  curshape,startpos
    if event & cv2.EVENT_LBUTTONDOWN == cv2.EVENT_LBUTTONDOWN:
        startpos = (x,y)
    elif  event & cv2.EVENT_LBUTTONUP == cv2.EVENT_LBUTTONUP:
        if curshape == 0:
            cv2.line(img,startpos,(x,y),(0,0,255),5)
        elif curshape == 1:
            cv2.rectangle(img,startpos,(x,y),(0,0,255),5)
        elif curshape == 2:
            a= (x-startpos[0])
            b= (y-startpos[1])
            r = int((a ** 2 + b ** 2) ** 0.5)
            cv2.circle(img,startpos,r,(0,0,255))
        else:
            print("无效的图形")



cv2.namedWindow('drawshape', cv2.WINDOW_NORMAL)
cv2.setMouseCallback('drawshape',mouse_callback,"123")



while True:
    # 转换颜色空间

    cv2.imshow('drawshape', img)
    key = cv2.waitKey(10) & 0xFF
    if key  == ord('q'):
        break
    elif key == ord('l'):
        curshape = 0
    elif key == ord('r'):
        curshape = 1
    elif key == ord('c'):
        curshape = 2
cv2.destroyAllWindows()