opencv-python在窗口用鼠标动态绘制直线、矩形、圆

 以下代码功能：创建窗口、在给定窗口显示图像、并在窗口上动态绘制直线、矩形、圆，类似labelme等标注工具画标注框。

缺陷：内存占用过高，有待优化，欢迎讨论并改进。

import numpy as np
import cv2

#1、创建窗口
cv2.namedWindow("demo1", cv2.WINDOW_NORMAL)
cv2.resizeWindow("demo1", 640, 480)
#2、创建图像、亦可cv2.imread读入
img = np.zeros((480, 640, 3), np.uint8)
img_backup = img.copy() #img的备份，防止画出叠叠框(类似千手观音)
start_point=(0,0)#起始点
state=-1 #标记量，0则画直线，1则画矩形，2则画圆
drawing=False #标记量、True表示开始画，False表示结束画
def onMouse(event, x, y, flags, param): #鼠标监听函数
    global start_point,state,drawing,img,img_backup #局部变量全局化
    if event==cv2.EVENT_LBUTTONDOWN: # 鼠标左键按下
        drawing=True
        start_point = (x, y)
    elif event==cv2.EVENT_MOUSEMOVE: #鼠标移动
        if drawing:#进入该层判断，改变了img，显示后要改回来，具体改回来的位置要位于图像显示之后
            if state==0:
                cv2.line(img, start_point, (x,y), (255,0,0), 2)
            elif state==1:
                cv2.rectangle(img, start_point, (x,y), (0,255,0), 2)
            elif state==2:
                radius=int(((start_point[0]-x)**2+(start_point[1]-y)**2)**0.5)
                cv2.circle(img, start_point, radius, (0,0,255), 2)
            else:
                print(f"state error: {state}")
    elif event==cv2.EVENT_LBUTTONUP: #鼠标左键抬起，只有进入此判断img才允许被改变
        drawing=False
        if state==0:
            cv2.line(img, start_point, (x,y), (255,0,0), 2)
        elif state==1:
            cv2.rectangle(img, start_point, (x,y), (0,255,0), 2)
        elif state==2:
            radius=int(((start_point[0]-x)**2+(start_point[1]-y)**2)**0.5)
            cv2.circle(img, start_point, radius, (0,0,255), 2)
        else:
            print(f"state error: {state}")
        img_backup=img.copy() # 备份图像更新

cv2.setMouseCallback("demo1",onMouse) #窗口和鼠标监听函数绑定

while True:
    cv2.imshow("demo1", img)
    if drawing:# 开始画后，鼠标移动，画完后吧img还原
        img=img_backup.copy()
    key = cv2.waitKey(1)
    if key==ord('q'):#按q退出
        break
    elif key==ord('l'):#按'l'画line
        state=0
    elif key==ord('r'):#按'r'画rectangle
        state=1
    elif key==ord('c'):#按'c'画circle
        state=2
cv2.destroyAllWindows()#窗口销毁