pygame_tut_16.py

# Move a single pixel around the screen without crashing against the border
import pygame

# These are used for directions

UP = (0, -1)
DOWN = (0, 1)
LEFT = (-1, 0)
RIGHT = (1, 0)

# Used for colors
BLACK_COLOR = (0,0,0)
WHITE_COLOR = (255,255,255)

class MovingPixel:
    """A moving pixel class."""

    def __init__(self, x, y):
        """Create a moving pixel."""
        self.x = x
        self.y = y
        self.hdir = 0
        self.vdir = -1

    def direction(self, dir):
        """Changes the pixel directions."""
        self.hdir, self.vdir = dir

    def move(self):
        """Moves the pixel."""
        self.x += self.hdir
        self.y += self.vdir

    def draw(self,surface):
        surface.set_at((self.x, self.y), WHITE_COLOR)

# Window dimensions

width = 640
height = 400

screen = pygame.display.set_mode((width, height))
clock = pygame.time.Clock()
running = True

# Create a moving pixel.

pix = MovingPixel(width/2, height/2)

while running:
    pix.move()

    if pix.x <= 0 or pix.x >= width or pix.y <=0 or pix.y >=height:
        print "Crash!"
        running = False

    screen.fill(BLACK_COLOR)
    pix.draw(screen)

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        elif event.type == pygame.KEYDOWN:
            if event.key == pygame.K_UP:
                pix.direction(UP)
            elif event.key == pygame.K_DOWN:
                pix.direction(DOWN)
            elif event.key == pygame.K_LEFT:
                pix.direction(LEFT)
            elif event.key == pygame.K_RIGHT:
                pix.direction(RIGHT)

    pygame.display.flip()
    clock.tick(0.24)