Introduction to mouse events in opencv

drawing_app_with_mouse.py

import numpy as np
import cv2 as cv

drawing = False # true if mouse is pressed
mode = True # if True, draw rectangle. Press 'm' to toggle to circle
ix,iy = -1,-1

# mouse callback function
def draw_circle(event,x,y,flags,param):
    global ix,iy,drawing,mode

    if event == cv.EVENT_LBUTTONDOWN:
        drawing = True
        ix,iy = x,y
    elif event == cv.EVENT_MOUSEMOVE:
        if drawing == True:
            if mode == True:
                cv.rectangle(img,(ix,iy),(x,y),(0,255,0),-1)
            else:
                cv.circle(img,(x,y),5,(0,0,255), -1)

    elif event == cv.EVENT_LBUTTONUP:
        drawing = False
        if mode == True:
            cv.rectangle(img,(ix,iy),(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',draw_circle)

while 1:
    cv.imshow('image',img)
    k = cv.waitKey(1) & 0xFF
    if k == ord('m'):
        mode = not mode
    elif k == 27:
        break

cv.destroyAllWindows()

intro_to_mouse_events.py

import numpy as np
import cv2 as cv

# mouse callback function
def draw_circle(event, x, y, flags, param):
    if event == cv.EVENT_LBUTTONDBLCLK:
        cv.circle(img, (x,y),100, (0,255,0), -1)

# Create a black image, a window and binf the function to window
img = np.zeros((512, 512, 3), np.uint8)

cv.namedWindow('image')
cv.setMouseCallback('image', draw_circle)

while 1:
    cv.imshow('image', img)
    if cv.waitKey(20) & 0xFF == 27:
        break

cv.destroyAllWindows()
~