Using Tkinter inside function not working

[darkv]

Hello iMuny, thanks for your suggestion.

I have done as you suggested and still no luck...

This is how it looks now:

from serial import *
from tkinter import *
import time

root = Tk() 
root.geometry("1280x800")
root.attributes('-fullscreen',True)
bg = PhotoImage(file = "/home/pi/Pictures/SCREEN2.png") 

canvas = Canvas( root, width = 1280, height = 800) 
canvas.pack(fill = "both", expand = True) 
canvas.create_image( 0, 0, image = bg, anchor = "nw") 

serialPort = "/dev/ttyUSB0"
ser = Serial(serialPort, 9600, timeout=0)
ser.flush()

def split_coords(astring):
    a, b = astring.split(';')
    a = int(a)
    b = int(b)
    
    return (a, b)

def paintRectangle1(canvas_ref):
    print("entered Rect 1")
    canvas_ref.create_rectangle(207, 151, 620, 374, fill='red')
    time.sleep(0.3)
    
def paintRectangle2(canvas_ref):
    print("entered Rect 2")
    canvas_ref.create_rectangle(600, 120, 800, 220, fill='red')
    time.sleep(0.3)
    
def paintRectangle3(canvas_ref):
    print("entered Rect 3")
    canvas_ref.create_rectangle(200, 260, 400, 360, fill='red')
    time.sleep(0.3)
    
def paintRectangle4(canvas_ref):
    print("entered Rect 4")
    canvas_ref.create_rectangle(600, 260, 800, 360, fill='red')
    time.sleep(0.3)

root.mainloop() 


while True:
    
    if ser.in_waiting> 0:
        line = ser.readline().decode('utf-8').rstrip()
        x, y = split_coords(line)
        print("x:", x, "- y:", y)
    
        canvas = Canvas( root, width = 1280, height = 800)
        
        if (x>19) and (x<60) and (y>20) and (y<40):
            print("OK button1")
            paintRectangle1(canvas)
        if (x>68) and (x<110) and (y>20) and (y<40):
            print("OK button2")
            paintRectangle2(canvas)
        if (x>19) and (x<60) and (y>45) and (y<80):
            print("OK button3")
            paintRectangle3(canvas)
        if (x>68) and (x<110) and (y>45) and (y<80):
            print("OK button4")
            paintRectangle4(canvas)
        '''    
        else:
            canvas.create_image( 0, 0, image = bg, anchor = "nw")

'''

and the error...

Error:
x: 11 - y: 11
Traceback (most recent call last):
  File "/home/pi/Documents/Touch-GUI-TKInter_4.py", line 55, in <module>
    canvas = Canvas( root, width = 1280, height = 800)
  File "/usr/lib/python3.7/tkinter/__init__.py", line 2405, in __init__
    Widget.__init__(self, master, 'canvas', cnf, kw)
  File "/usr/lib/python3.7/tkinter/__init__.py", line 2299, in __init__
    (widgetName, self._w) + extra + self._options(cnf))
_tkinter.TclError: can't invoke "canvas" command: application has been destroyed

same here. did you found the solution