def draw_circle(event,x,y,flags,param):  global ix,iy,drawing,mode,start_x,start_y  if event == cv2.EVENT_LBUTTONDOWN:    if drawing == False:      start_x, start_y = x,y      ix,iy = x,y      drawing = True    elif drawing == True:      cv2.line(img,(ix,iy),(x,y),(0,255,0),3)      ix, iy = x, y    print(drawing)  elif event == cv2.EVENT_MBUTTONDOWN:    drawing = False    cv2.line(img, (ix, iy), (start_x, start_y), (0, 255, 0), 3)    print(drawing)  #  # elif event == cv2.EVENT_RBUTTONUP:  #   cv2.line(img,(ix,iy),(x,y),(0,255,0),3)# Next we have to bind this mouse callback function to OpenCV # # window. In the main loop, we should set a keyboard binding for# key ‘m' to toggle between rectangle and circle.img = np.zeros((512,512,3), np.uint8)cv2.namedWindow('image')cv2.setMouseCallback('image',draw_circle)while(1):  cv2.imshow('image',img)  k = cv2.waitKey(1) & 0xFF  if k == ord('m'): # 切換模式    mode = not mode  elif k == 27:    breakcv2.destroyAllWindows()