draw_rect_diff_mouse_events.py

import cv2
import numpy as np

drawing = False
ix , iy = -1 , -1

def draw_rectangle(event,x,y,flags,param):
    global ix, iy, drawing
    if event == cv2.EVENT_LBUTTONDOWN:
        drawing = True
        ix,iy = x,y
    elif event == cv2.EVENT_MOUSEMOVE:
        if drawing:
            cv2.rectangle(img, (ix,iy), (x,y), (0,255,0), -1)
    elif event == cv2.EVENT_LBUTTONUP:
        drawing = False
        cv2.rectangle(img, (ix,iy), (x,y), (0,255,0), -1)



img = np.zeros(shape=(512,512,3))
cv2.namedWindow(winname = 'my_drawing')
cv2.setMouseCallback('my_drawing',draw_rectangle)

while(True):
    cv2.imshow('my_drawing', img)
    if cv2.waitKey(1) & 0xFF == 27:
        break
cv2.destroyAllWindows()