Simple animation with Tkinter Python

Question

I've searched for a simple animation code with Tkinter but I've found very different examples and I can't understand the correct way to write an animation. Here my working code to display a simple moving circle:

import tkinter as tk
import time

root=tk.Tk()
canvas=tk.Canvas(root,width=400,height=400)
canvas.pack()
circle=canvas.create_oval(50,50,80,80,outline="white",fill="blue")

def redraw():
   canvas.after(100,redraw)
   canvas.move(circle,5,5)
   canvas.update()
canvas.after(100,redraw)
root.mainloop()

In this code I can't correctly understand: how the after method works, where correctly put the update and the move method (before after method ?), is there another way to write an animation code? may you post me another example and comment the code please? Thanks :)

the update is doing nothing, what do you want to happen exactly? — Padraic Cunningham
– Padraic Cunningham, Commented Mar 22, 2015 at 15:05
I need a simple animation, create a polygon and move it in my app — Cassandra
– Cassandra, Commented Mar 23, 2015 at 15:19
@PadraicCunningham: it doesn't do nothing -- it actually does something. It processes all pending events. — Bryan Oakley
– Bryan Oakley, Commented Mar 25, 2015 at 19:57
@PadraicCunningham: Like I said, it processes all pending events. In this specific case it's harmless since there are no event bindings, but "harmless" isn't the same as "nothing" because it actually does process any pending events. It does the same work as mainloop, but it does it just once rather than continually. — Bryan Oakley
– Bryan Oakley, Commented Mar 25, 2015 at 20:10

Bryan Oakley · Accepted Answer · 2022-05-13 02:56:59Z

1

Calling update

You should not call canvas.update(). As a general rule of thumb you should never call update. For a short essay on why, see this essay written by one of the original developers of the underlying tcl interpreter.

If you take out the call to canvas.update(), you have the proper way to do animation in a tkinter program.

Calling after to start the animation

You don't need to call after immediately before calling root.mainloop(). This works just as well:

...
redraw()
root.mainloop()

The choice to use or not use after in this specific case is dependent on if you want the animation to start immediately (possibly even before the widget is visible) or if you want it to happen after a short delay (possibly after the widget is made visible)

How after works

mainloop is nothing more than an infinite loop that checks the event queue for events. When it finds an event, it pops it off of the list and processes it. after is nothing more than making a request that says "in 100 ms, please add a new event to the queue". When the time limit expires, an event is added to the queue that says, in effect, "run this command". The next time the loop checks for events, it sees this event, pulls it off of the queue, and runs the command.

When you call after from within a method that itself was called by after, you're saying in effect "wait 100ms and do it again", creating an infinite loop. If you put the call to after before moving the object, you're saying "every 100ms run this function". If you put it after you're saying "run this function 100 ms after the last time it was run". The difference is very subtle and usually not perceptible unless your function takes a long time to run.

edited May 13, 2022 at 2:56

answered Mar 25, 2015 at 19:56

Bryan Oakley

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2 Comments

ChronoVortex Over a year ago

Is there a reason why you should never call .update? It seems like a pretty useful thing to use to force an animation to be shown on the screen if you're changing things within a loop, for example making a loading screen.

Bryan Oakley Over a year ago

@RedstoneReforged: this essay by someone who wrote some of the internals of the underlying tcl interpreter is probably the best explanation there is.

Enek · Accepted Answer · 2017-09-02 09:01:13Z

0

my code is:

from tkinter import *
import time
tk = Tk()
płótno = Canvas(tk, width=500, height=500)
płótno.pack()
płótno.create_polygon(10,10,10,70,70,10,fill="blue",outline="black")
for x in range(0,51):
   płótno.move(1,5,0)
   płótno.update()
   rest(0.05)

płótno means canvas

answered Sep 2, 2017 at 9:01

Enek

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