Tkinter canvas flickering

Question

I'm attempting to implement a simple Pong game in Python using Tkinter, but unfortunately I'm having some major issues with flickering. I'm using a Canvas widget that covers the entire window and I'm drawing rectangles on said canvas many times per second. When I do this all drawn rectangles flicker regularly while the game is running, disappearing for a fraction of a second before appearing again.

A simple example of the logic I use for drawing in my game can be seen below, by running it you should be able to see the flickering in action:

from tkinter import *
import threading, time

def loop():
    FRAME_TIME = 1 / 60
    while True:
        render()
        time.sleep(FRAME_TIME)

def render():
    canvas.delete(ALL)
    canvas.create_rectangle(0, 0, WIDTH, HEIGHT, fill='black')

WIDTH = 800
HEIGHT = 600

root = Tk()
canvas = Canvas(root, width=800, height=600)
canvas.pack()
threading.Thread(target=loop, daemon=True).start()
root.mainloop()

Any ideas as to what is causing it?

You don't need a thread to do this. Also, don't delete and recreate a rectangle, just move it. See http://stackoverflow.com/a/25431690/7432 for an example of the proper way to do animation with tkinter. — Bryan Oakley, Dec 23 '16 at 23:53
@Bryan Oakley. Thanks, your comment solved my problem. Shame I don't have an answer to accept. — Just some guy, Dec 25 '16 at 13:19

score 1 · Answer 1 · answered Aug 07 '20 at 16:32

The threading is totally not needed for your script (The Tkinter doesn't love the threading).

You should use the widget.after() instead of infinite for loop.

I guess you should define the canvas and the rectangle on the canvas and in a function you should move the other widgets. In this case you shouldn't delete/recreate the widgets.

The black "background" (rectangle) is static and it is not updated during the script running. An oval widget has been created on the canvas (create_oval()) and this widget moves in the render function (randomly change the X-Y positions between -3 and 3).

The canvas.after(10, render) means to call again-and-again the render function in every 10 secs. So actually it is an animation and the oval will move always on your canvas.

Example:

from tkinter import *
import random


def render():
    canvas.move(oval, random.randint(-3, 3), random.randint(-3, 3))
    canvas.after(10, render)


WIDTH = 800
HEIGHT = 600

root = Tk()
canvas = Canvas(root, width=800, height=600)
canvas.create_rectangle(0, 0, WIDTH, HEIGHT, fill="black")
oval = canvas.create_oval(400, 400, 410, 410, fill="red")
canvas.pack()
render()
root.mainloop()

GUI:

I think it is a good starting point for you to implement the complete pong game.

+1 "`Tkinter` doesn't love the threading". This is very true and over the years has caused the _tkinter module to have many a work-around added. The current situation is a careful balance of a tkinter exclusive mutex and the GIL but you can still crash the CPython interpreter using threads with tkinter in some situations. Summary: avoid this combination if possible. — Minion Jim, Aug 07 '20 at 16:57
I totally agree with you. I hope this tk/python situation will be a funny memory is heads is the future! :) — milanbalazs, Aug 07 '20 at 18:54

Tkinter canvas flickering

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