CODEWITHSUNDEEP
pythontkinter
Fergal Bernard
Fergal Bernard

Reputation: 13

Why does my tkinter oval accelerate despite having a fixed speed?

I'm trying to make this oval move fluidly on this canvas using tkinter, but despite having a fixed speed, it seems to accelerate the more I move it. Even when debugging I've noticed that my speed variables do not increase above the desired values. I can't manage to identify what is causing this acceleration, can someone please point out what's going on?

Here's my code:

from tkinter import*

window = Tk()
canvas = Canvas(window, width = 300, height = 300, bg ='white')
canvas.focus_set()

speedx = 0
speedy = 0
speed = 1

x1=40
y1=40

oval=canvas.create_oval(x1-10,y1-10,x1+10,y1+10,width=2,fill='orange')

def key_press(event):
    global x1, y1
    global speedx, speedy, speed

    button = event.keysym
    if button == 'Up':
        speedx = 0
        speedy = -speed
    elif button == 'Down':
        speedx = 0
        speedy = speed
    elif button == 'Right':
        speedx = speed
        speedy = 0
    elif button == 'Left':
        speedx = -speed
        speedy = 0
    move()

def move():
    global x1,y1
    global oval
    global speedx, speedy
    x1 += speedx
    y1 += speedy
    canvas.delete(oval)
    oval = canvas.create_oval(x1+10,y1-10,x1-10,y1+10,width=2,fill='orange')
    window.after(10, move)

def key_release(event):
    global speedx, speedy
    speedx = 0
    speedy = 0


canvas.bind('<KeyPress>', key_press)
canvas.bind("<KeyRelease>", key_release)
canvas.pack(padx =5, pady =5)
window.mainloop()

Upvotes: 1

Views: 166

Answers (1)

fhdrsdg
fhdrsdg

Reputation: 10572

The problem is that you call window.after(10, move) from within your move function without ever cancelling it again. This generates a never ending loop of calls to move for every <KeyPress> event.

What you could do is to save the after call to a variable. With this you can make sure that move isn't called again from outside this loop, plus you can use it to cancel the after call on the key's release:

from tkinter import *

window = Tk()
canvas = Canvas(window, width = 300, height = 300, bg ='white')
canvas.focus_set()

speedx = 0
speedy = 0
speed = 1

# Make variable to store after call object
after_obj = None

x1=40
y1=40

oval=canvas.create_oval(x1-10,y1-10,x1+10,y1+10,width=2,fill='orange')

def key_press(event):
    global x1, y1
    global speedx, speedy, speed
    global after_obj
    button = event.keysym
    if button == 'Up':
        speedx = 0
        speedy = -speed
    elif button == 'Down':
        speedx = 0
        speedy = speed
    elif button == 'Right':
        speedx = speed
        speedy = 0
    elif button == 'Left':
        speedx = -speed
        speedy = 0
    # Only call move from here if there is no after scheduled
    if after_obj is None:
        move()

def move():
    global x1,y1
    global oval
    global speedx, speedy
    global after_obj
    x1 += speedx
    y1 += speedy
    canvas.delete(oval)
    oval = canvas.create_oval(x1+10,y1-10,x1-10,y1+10,width=2,fill='orange')
    # Save the after call object
    after_obj = window.after(10, move)

def key_release(event):
    global speedx, speedy  
    global after_obj
    # When pressing multiple buttons at the same time you can get a key release without an after_obj, so check if it exists then cancel it
    if after_obj:
        window.after_cancel(after_obj)
    # Reset after_obj to None so move can be called from key_press again
    after_obj = None
    speedx = 0
    speedy = 0


canvas.bind('<KeyPress>', key_press)
canvas.bind("<KeyRelease>", key_release)
canvas.pack(padx =5, pady =5)
window.mainloop()

Upvotes: 1

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