#import opencv and numpy

import cv2  

import numpy as np

​

#trackbar callback fucntion does nothing but required for trackbar

​

​

​

def nothing(x):

    pass 

​

def change_color(x):

    #condition to change color if trackbar value is greater than 127 

    if(cv2.getTrackbarPos('r','controls')>127):

        global color

        color=(255,0,0)

    else:

        color=(0,0,255)

​

#create a seperate window named 'controls' for trackbar

cv2.namedWindow('controls')

#create trackbar in 'controls' window with name 'r''

cv2.createTrackbar('r','controls',15,255,change_color)

cv2.createTrackbar('s','controls',0,1,nothing)

​

#initial color

color=(0,0,255)

​

​

while(1):

    #create a black image 

    img = np.zeros((512,512,3), np.uint8)

    #calculate center of image

    img_center_y=img.shape[0]//2

    img_center_x=img.shape[1]//2

​

​

​

    #returns current position/value of trackbar 

    radius= int(cv2.getTrackbarPos('r','controls'))

    #returns current slider value of trackbar 's'

    shape=cv2.getTrackbarPos('s','controls')

​

    #checks if shape varible is off (0) or on (1)

    #draw square if switch is on

    if(shape==1): 

        start_point=(img_center_y-100,img_center_x-100)

        end_point=(img_center_y+100,img_center_x+100)

        #change thickness of square based in trackbar 'r'

        thickness = radius

        #create a square

        image = cv2.rectangle(img, start_point, end_point, color, thickness) 

        pass

    #draw circle if switch is off

    else:

        #draw a red circle 

        cv2.circle(img,(img_center_y,img_center_x), radius, color, -1)

    #show the image window

    cv2.imshow('img',img)

    #waitfor the user to press escape and break the while loop 

    k = cv2.waitKey(1) & 0xFF

    if k == 27:

        break

#destroys all window

cv2.destroyAllWindows()