pygame / examples_pygame / stars.py

#!/usr/bin/env python

"""A simple starfield example. Note you can move the 'center' of
the starfield by leftclicking in the window. This example show
the basics of creating a window, simple pixel plotting, and input
event management"""


import random, math, pygame
from pygame.locals import *

#constants
WINSIZE = [640, 480]
WINCENTER = [320, 240]
NUMSTARS = 150


def init_star():
	"creates new star values"
	dir = random.randrange(100000)
	velmult = random.random()*.6+.4
	vel = [math.sin(dir) * velmult, math.cos(dir) * velmult]
	return vel, WINCENTER[:]


def initialize_stars():
	"creates a new starfield"
	stars = []
	for x in range(NUMSTARS):
		star = init_star()
		vel, pos = star
		steps = random.randint(0, WINCENTER[0])
		pos[0] = pos[0] + (vel[0] * steps)
		pos[1] = pos[1] + (vel[1] * steps)
		vel[0] = vel[0] * (steps * .09)
		vel[1] = vel[1] * (steps * .09)
		stars.append(star)
	move_stars(stars)
	return stars
	

def draw_stars(surface, stars, color):
	"used to draw (and clear) the stars"
	for vel, pos in stars:
                pos = (int(pos[0]), int(pos[1]))
		surface.set_at(pos, color)


def move_stars(stars):
	"animate the star values"
	for vel, pos in stars:
		pos[0] = pos[0] + vel[0]
		pos[1] = pos[1] + vel[1]
		if not 0 <= pos[0] <= WINSIZE[0] or not 0 <= pos[1] <= WINSIZE[1]:
			vel[:], pos[:] = init_star()
		else:
			vel[0] = vel[0] * 1.05
			vel[1] = vel[1] * 1.05
	

def main():
	"This is the starfield code"
	#create our starfield
	random.seed()
	stars = initialize_stars()
        clock = pygame.time.Clock()
	#initialize and prepare screen
	pygame.init()
	screen = pygame.display.set_mode(WINSIZE)
	pygame.display.set_caption('pygame Stars Example')
	white = 255, 240, 200
	black = 20, 20, 40
	screen.fill(black)

	#main game loop
	done = 0
	while not done:
		draw_stars(screen, stars, black)
		move_stars(stars)
		draw_stars(screen, stars, white)
		pygame.display.update()
		for e in pygame.event.get():
			if e.type == QUIT or (e.type == KEYUP and e.key == K_ESCAPE):
				done = 1
				break
			elif e.type == MOUSEBUTTONDOWN and e.button == 1:
				WINCENTER[:] = list(e.pos)
                clock.tick(50)


# if python says run, then we should run
if __name__ == '__main__':
	main()
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