How to make a ball go around the edge of the screen continuously? (Python 2.7)
<p>I need help with my animation code. So far i have the ball go around 3 edges of the screen. But i don't know how to make it go around the last screen. </p>

<pre><code>#-------------------------------------------------------------------------------
# Name:        U1A4.py
# Purpose:     To animate the ball going around the edge of the screen
#-------------------------------------------------------------------------------

import pygame
import sys
pygame.init()

# Screen
screenSize = (800,600)
displayScreen = pygame.display.set_mode(screenSize,0)
pygame.display.set_caption("Animation Assignment 1")

# Colours
WHITE = (255,255,255)
GREEN = (0,255,0)
RED = (255,0,0)
BLUE = (0,0,255)

displayScreen.fill(WHITE)
pygame.display.update()

# ----------------- Leave animation code here ---------------------------------#

# THU/09/29
# Need to complete the last turn with the ball

x = 50
y = 50
dx = 0
dy = 2
stop = False
while not stop:
    for event in pygame.event.get():
        if event.type ==pygame.QUIT:
            stop = True

    displayScreen.fill(WHITE)

    x = x + dx
    y = y + dy

    if (x&gt;=750):
            dx = 0
            dy = -2

    if (y&gt;=550)and dy&gt;0:
            dy = 0
            dx = 2

    if (x&gt;=750)and dy&gt;0:
            dy = 0
            dx = 2

    if (y&gt;=550)and dy&gt;0:
            dx = 0
            dy = -2


    pygame.draw.circle(displayScreen, GREEN, (x,y),50, 0)
    pygame.display.update()

pygame.quit()
sys.exit()
</code></pre>

<p>The ball needs to go around the border of the screen continuously, any hints or direct answers are welcome. Thanks.</p>

<p>The ball only changes directions in the corners, so you just need to cover four cases (two <code>if</code>'s nested in two <code>if</code>'s):</p>

<pre><code>x += dx
y += dy

if x &gt;= 750:
  if y &gt;= 550:
    dx = 0
    dy = -2
  elif y &lt;= 50:
    dx = -2
    dy = 0
elif x &lt;= 50:
  if y &gt;= 550:
    dx = 2
    dy = 0
  elif y &lt;= 50:
    dx = 0
    dy = 2
</code></pre>

python python-2.7 pygame