```"""
Bounces a rectangle around the screen.

Sample Python/Pygame Programs
Simpson College Computer Science
http://simpson.edu/computer-science/

Explanation video: http://youtu.be/-GmKoaX2iMs
"""

import pygame

# Define some colors
BLACK = (0, 0, 0)
WHITE = (255, 255, 255)
GREEN = (0, 255, 0)
RED = (255, 0, 0)

pygame.init()

# Set the height and width of the screen
size = [700, 500]
screen = pygame.display.set_mode(size)

pygame.display.set_caption("Bouncing Rectangle")

# Loop until the user clicks the close button.
done = False

# Used to manage how fast the screen updates
clock = pygame.time.Clock()

# Starting position of the rectangle
rect_x = 50
rect_y = 50

# Speed and direction of rectangle
rect_change_x = 2
rect_change_y = 2

# -------- Main Program Loop -----------
while not done:
# --- Event Processing
for event in pygame.event.get():
if event.type == pygame.QUIT:
done = True

# --- Logic
# Move the rectangle starting point
rect_x += rect_change_x
rect_y += rect_change_y

# Bounce the ball if needed
if rect_y > 450 or rect_y < 0:
rect_change_y = rect_change_y * -1
if rect_x > 650 or rect_x < 0:
rect_change_x = rect_change_x * -1

# --- Drawing
# Set the screen background
screen.fill(BLACK)

# Draw the rectangle
pygame.draw.rect(screen, WHITE, [rect_x, rect_y, 50, 50])
pygame.draw.rect(screen, RED, [rect_x + 10, rect_y + 10, 30, 30])

# --- Wrap-up
# Limit to 60 frames per second
clock.tick(60)

# Go ahead and update the screen with what we've drawn.
pygame.display.flip()

# Close everything down
pygame.quit()

```
﻿