Paint application with adjustable colors

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please help with this example exercise ,Create a Paint application with adjustable colors and brush radius using trackbars. For drawing, refer previous tutorial on mouse handling. i am stuck making trackbar change the color of cv2.drawCirle() fxn

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i am trying to add an erase function where a green rectangle acts as an eraser, pressing "m" switches between draw circle and draw rectangle. pressing the left mouse button allows drawing while releasing stops drawing then adjust the track bar for other collors to draw on the window

this is my code:

import cv2
import numpy as np

drawing = True

ix,iy = -1,-1
erase= True






def paint(event,x,y,glags,param):
    global ix,iy,drawing,erase,trackbar

    if event == cv2.EVENT_LBUTTONDOWN:
        drawing = True
        ix,iy = x,y

    elif event == cv2.EVENT_MOUSEMOVE:
        if drawing == True:
            if erase == False:
               cv2.circle(img,(x,y),2,(0,0,255),-1)

               def nothing(x):
                return()


               trackbar = np.zeros((300,512,3), np.uint8)
               cv2.namedWindow("trackbar")
               cv2.createTrackbar('R','trackbar',0,255,nothing)
               cv2.createTrackbar('G','trackbar',0,255,nothing)
               cv2.createTrackbar('B','trackbar',0,255,nothing)

            else:
               cv2.rectangle(img,(x,y),(ix,iy),(0,120,0),-1)

    elif event == cv2.EVENT_LBUTTONUP:
        drawing = False


img = np.zeros((512,512,3), np.uint8)
cv2.namedWindow('image')
cv2.setMouseCallback('image',paint)

while(1):
        cv2.imshow('image',img)


        r = cv2.getTrackbarPos('R','trackbar')
        g = cv2.getTrackbarPos('G','trackbar')
        b = cv2.getTrackbarPos('B','trackbar')

        k = cv2.waitKey(1) & 0xFF
        if k == ord('m'):
             erase = not erase
        elif k == 27:
            break
cv2.destroyAllWindows()