Starfield-like effect

starfield.py

import math
import random

import pygame

class Star(pygame.sprite.Sprite):
    def __init__(self, center, r, angle):
        super().__init__()
        self.center = center
        self.angle = angle
        self.dist0 = self.dist = r
        self.r = random.randrange(2, 6)
        self.speed = random.randint(1, 5)

        self.image = pygame.Surface((self.r * 2, self.r * 2), pygame.SRCALPHA)
        pygame.draw.circle(self.image, (192, 255, 255), (self.r, self.r), self.r, width=0)
        pygame.draw.circle(self.image, (0, 128, 128), (self.r, self.r), self.r, width=2)

    def update(self, dt):
        self.dist += self.speed * dt / 40
        self.angle += self.speed * dt / 40000
        self.speed *= 1.1
        x = self.center[0] + math.sin(self.angle) * self.dist
        y = self.center[1] + math.cos(self.angle) * self.dist
        self.rect = self.image.get_rect(center=(x, y))

        if x < 0 or x > PGMTest.WIDTH or y < 0 or y > PGMTest.HEIGHT:
            self.reset()

    def reset(self):
        self.dist = self.dist0
        self.angle = random.random() * math.pi * 2
        self.speed = random.randint(1, 5)


class Glow(pygame.sprite.Sprite):
    def __init__(self, center, r, angle):
        super().__init__()
        self.center = center
        self.angle = angle
        self.dist0 = self.dist = r
        self.r = random.randrange(6, 12)
        self.speed = random.randint(15, 25)

        self.image = pygame.Surface((self.r * 2, self.r * 2), pygame.SRCALPHA)
        pygame.draw.circle(self.image, (255, random.randrange(78, 220), 1), (self.r, self.r), self.r, width=0)
        pygame.draw.circle(self.image, (255, 78, 1), (self.r, self.r), self.r, width=1)

    def update(self, dt):
        self.angle += self.speed * dt / 40000
        x = self.center[0] + math.sin(self.angle) * self.dist
        y = self.center[1] + math.cos(self.angle) * self.dist
        self.rect = self.image.get_rect(center=(x, y))


class PGMTest:
    WIDTH = 1280
    HEIGHT = 600
    def prepare_window(self):
        self.screen = pygame.display.set_mode((self.WIDTH, self.HEIGHT))
        self.screen.fill((0, 0, 255))

    def prepare_particles(self, x, y, r):
        self.particles = pygame.sprite.Group()
        for i in range(500):
            angle = random.random() * math.pi * 2
            self.particles.add(Star((x, y), r, angle))
            self.particles.add(Glow((x, y), r, angle))

    def run(self):
        dt = 1
        clock = pygame.time.Clock()
        do_run = True
        self.prepare_particles(self.WIDTH / 2, self.HEIGHT / 2, self.HEIGHT // 3)
        while do_run:
            for event in pygame.event.get():
                if event.type == pygame.QUIT:
                    do_run = False
                    break
            self.screen.fill((0, 0, 0))
            self.particles.update(dt=dt)
            self.particles.draw(self.screen)

            pygame.display.flip()
            dt = clock.tick(60)

if "__main__" == __name__:
    pygame.init()
    pgm = PGMTest()
    pgm.prepare_window()
    pgm.run()
    pygame.quit()