import cv2 as cv
import numpy as np

drawing = False # 是否开始画图
mode = True # True：画矩形，False：画圆
start = (-1, -1)

# 鼠标的回调函数的参数格式是固定的，不要随意更改。
def mouse_event(event, x, y, flags, param):
  global start, drawing, mode

  # 左键按下：开始画图
  if event == cv.EVENT_LBUTTONDOWN:
    drawing = True
    start = (x, y)
  # 鼠标移动，画图
  elif event == cv.EVENT_MOUSEMOVE:
    if drawing:
      if mode:
        cv.rectangle(img, start, (x, y), (0, 255, 0), -1)
      else:
        cv.circle(img, (x, y), 5, (0, 0, 255), -1)
  # 左键释放：结束画图
  elif event == cv.EVENT_LBUTTONUP:
    drawing = False
    if mode:
      cv.rectangle(img, start, (x, y), (0, 255, 0), -1)
    else:
      cv.circle(img, (x, y), 5, (0, 0, 255), -1)


img = np.zeros((512, 512, 3), np.uint8)
cv.namedWindow('image')
cv.setMouseCallback('image', mouse_event)

while(True):
  cv.imshow('image', img)
  # 按下m切换模式
  if cv.waitKey(1) == ord('m'):
    mode = not mode
  # 按ESC键退出程序
  elif cv.waitKey(1) == 27:
    break