rectangle.py

import pygame
import sys
from pygame.locals import *
pygame.init()
screen = pygame.display.set_mode((600, 500))
pygame.display.set_caption("Drawing Rectangles")
i = 0
pos_x = 300
pos_y = 250
vel_x = 2
vel_y = 1
while True:
	for event in pygame.event.get():
		if event.type in (QUIT, KEYDOWN):
			sys.exit()
	
	screen.fill((0, 0, 200))
	
	#move the rectangle
	pos_x += vel_x
	pos_y += vel_y
	
	#keep rectangle on the screen
	if pos_x > 500 or pos_x < 0:
		vel_x = -vel_x
		i += 1
		if i > 3:
			i = 0
	if pos_y > 400 or pos_y < 0:
		vel_y = -vel_y
		
	#draw the rectangle
	color = [(255, 255, 0), (255, 0, 0), (0, 255, 0), (255, 0, 255)]
	width = 0 #solid fill
	pos = pos_x, pos_y, 100, 100
	pygame.draw.rect(screen, color[i], pos, width)
	
	pygame.display.update()