Simple Starfield with Python and Pygame

In this tutorial we will create a simple but cool starfield simulation with Python and Pygame. The tutorial will be very brief and accompanied by a self-explanatory small amount of code. See below a video of the simulation in action.

The Idea

To simulate the effect, we start by creating a list of stars positioned randomly across the screen. Then, in the main loop, we continuously move and draw the stars. When a star crosses the bottom screen border, we create a new star at the top of the screen.

The Code

The code is small and clear,  and therefore bears a small amount of explanation. The init() function creates a list of stars positioned randomly across the screen. The move_and_draw_stars() function moves and draws the stars. When moving a star, move_and_draw_stars() checks if the star has crossed the bottom border. If so, it creates a new star at the top of the screen.

import pygame
from random import randrange

MAX_STARS  = 250
STAR_SPEED = 2

def init_stars(screen):
  """ Create the starfield """
  global stars
  stars = []
  for i in range(MAX_STARS):
    # A star is represented as a list with this format: [X,Y]
    star = [randrange(0,screen.get_width() - 1),
            randrange(0,screen.get_height() - 1)]
    stars.append(star)

def move_and_draw_stars(screen):
  """ Move and draw the stars in the given screen """
  global stars
  for star in stars:
    star[1] += STAR_SPEED
    # If the star hit the bottom border then we reposition
    # it in the top of the screen with a random X coordinate.
    if star[1] >= screen.get_height():
      star[1] = 0
      star[0] = randrange(0,639)

    screen.set_at(star,(255,255,255))

def main():
  # Pygame stuff
  pygame.init()
  screen = pygame.display.set_mode((640,480))
  pygame.display.set_caption("Starfield Simulation")
  clock = pygame.time.Clock()

  init_stars(screen)

  while True:
    # Lock the framerate at 50 FPS
    clock.tick(50)

    # Handle events
    for event in pygame.event.get():
      if event.type == pygame.QUIT:
        return

    screen.fill((0,0,0))
    move_and_draw_stars(screen)
    pygame.display.flip()

if __name__ == "__main__":
  main()

Click here to download the source code.

Conclusion

That’s everything for now. In the next tutorial I will show you how to make a parallax starfield.

To stay updated, make sure you subscribe to this blog,  follow us on twitter, or follow us on facebook.