mouse_drawing_p3.py

import cv2
import numpy as np

#################
##  VARIABLES  ##
#################

# true while mouse down, false while mouse up
drawing = False
ix,iy = -1,-1

#################
##  FUNCTION  ###
#################

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 == True:
            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)


##################################
##  SHOWING IMAGE WITH OPENCV   ##
##################################

img = np.zeros((512,512,3))

cv2.namedWindow(winname='my_drawing')

cv2.setMouseCallback('my_drawing',draw_rectangle)

while True:

    cv2.imshow('my_drawing',img)

    # check for hitting esc key
    if cv2.waitKey(1) & 0xFF == 27:
        break

cv2.destroyAllWindows()