simu.py

import random,pygame,PyParticles

class UniverseScreen:
    def __init__ (self, width, height):
        self.width = width
        self.height = height
        (self.dx, self.dy) = (0, 0)
        (self.mx, self.my) = (0, 0)
        self.magnification = 1.0
        
    def scroll(self, dx=0, dy=0):
        self.dx += dx * width / (self.magnification*10)
        self.dy += dy * height / (self.magnification*10)
        
    def zoom(self, zoom):
        self.magnification *= zoom
        self.mx = (1-self.magnification) * self.width/2
        self.my = (1-self.magnification) * self.height/2
        
    def reset(self):
        (self.dx, self.dy) = (0, 0)
        (self.mx, self.my) = (0, 0)
        self.magnification = 1.0
        
def calculateRadius(mass):
    return 0.5 * mass ** (0.5)

(width, height) = (1300, 690)
screen = pygame.display.set_mode((width, height))
pygame.display.set_caption('Star formation')

universe = PyParticles.Environment((width, height))
universe.colour = (0,0,0)
universe.addFunctions(['move', 'attract', 'combine'])
universe_screen = UniverseScreen(width, height)

for p in range(100):
    particle_mass = random.randint(1,4)
    particle_size = calculateRadius(particle_mass)
    universe.addParticles(mass=particle_mass, size=particle_size, speed=2, colour=(255,255,255))

key_to_function = {
    pygame.K_LEFT:   (lambda x: x.scroll(dx = 1)),
    pygame.K_RIGHT:  (lambda x: x.scroll(dx = -1)),
    pygame.K_DOWN:   (lambda x: x.scroll(dy = -1)),
    pygame.K_UP:     (lambda x: x.scroll(dy = 1)),
    pygame.K_EQUALS: (lambda x: x.zoom(2)),
    pygame.K_MINUS:  (lambda x: x.zoom(0.5)),
    pygame.K_r:      (lambda x: x.reset())}

clock = pygame.time.Clock()
paused = False
running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        if event.type == pygame.KEYDOWN:
            if event.key in key_to_function:
                key_to_function[event.key](universe_screen)
            elif event.key == pygame.K_SPACE:
                paused = not paused

    if not paused:
        universe.update()
        
    screen.fill(universe.colour)
    
    particles_to_remove = []
    for p in universe.particles:
        if 'collide_with' in p.__dict__:
            particles_to_remove.append(p.collide_with)
            p.size = calculateRadius(p.mass)
            del p.__dict__['collide_with']

        x = int(universe_screen.mx + (universe_screen.dx + p.x) * universe_screen.magnification)
        y = int(universe_screen.my + (universe_screen.dy + p.y) * universe_screen.magnification)
        size = int(p.size * universe_screen.magnification)
        
        if size < 2:
            pygame.draw.rect(screen, p.colour, (x, y, 2, 2))
        else:
            pygame.draw.circle(screen, p.colour, (x, y), size, 0)
    
    for p in particles_to_remove:
        if p in universe.particles:
            universe.particles.remove(p)

    pygame.display.flip()
    clock.tick(80)