a very small learning project to have a snowing screensaver.

snowstorm.py

#!/usr/bin/env python
"""a very small learning project to have a snowing screensaver."""

import random
import pygame.gfxdraw


class Snowflake:
    """Representation of a single snowflake."""

    MEAN_SIZE = 3
    MAX_SIZE = 15

    def __init__(self, max_x, max_y):
        """
        create a new snow flake

        :param max_x: screen width to draw on
        :param max_y: screen height to draw on
        """
        self.x = None
        self.y = None
        self.r = None
        self.color = None
        self.max_x = max_x
        self.max_y = max_y
        self.generate_new_parameters()

    def generate_new_parameters(self):
        """
        reposition a snowflake above the actual screen,
        and resize it randomly

        :return: None
        """
        self.x = random.randrange(self.max_x)
        self.y = random.randrange(-self.max_y, 0)
        self.r = random.randrange(1, self.MAX_SIZE)
        self.r = int(min(random.expovariate(1 / self.MEAN_SIZE) + 1, self.MAX_SIZE))
        intensity = random.randint(50, 255)
        self.color = pygame.Color(intensity, intensity, intensity, 0)

    def progress_color(self):
        """
        increase opacity as the flake falls down

        :return: None
        """
        alpha = int(255 * self.y / self.max_y)
        alpha = sorted([50, alpha, 255])[1]
        self.color.a = alpha

    def move(self, wind, max_x, max_y):
        """
        move a snowflake downwards, respecting horizontal wind

        :param wind: wind speed for horizontal movement
        :param max_x: screen width to draw on
        :param max_y: screen height to draw on
        :return: None
        """
        self.max_x = max_x
        self.max_y = max_y
        self.x += int(wind / self.r)
        self.y += self.MAX_SIZE + 1 - self.r
        self.enforce_periodic_boundaries()
        self.progress_color()

    def enforce_periodic_boundaries(self):
        """
        let a snowflake appear on one side of the screen
        if it disappears on the other.
        Also let it "respawn" if it fell past the screen

        :return: None
        """
        if (self.x < 0 - self.r) or (self.x > (self.max_x + self.r)):
            self.x = self.max_x - self.x
        if self.y > self.max_y + self.r:
            self.generate_new_parameters()

    def __getitem__(self, key):
        """
        Makes the class iterable.
        Enables the use of *snowflake for the current parameters

        :param key: index to get: 0=>x, 1=>y, 2=>r, 3=>color
        :return: the value connected to the index
        """
        current_state = (self.x, self.y, self.r, self.color)
        return current_state[key]


class SnowingApp:
    """
    provides the pygame abstraction to have a little snowstorm
    """
    BACKGROUND_COLOR = pygame.color.THECOLORS['black']
    FPS = 30

    def __init__(self, canvas, snow_amount, wind_speed):
        self.canvas = canvas
        self.wind_speed = wind_speed
        screen_size = pygame.display.Info()
        self.screen_width = screen_size.current_w
        self.screen_height = screen_size.current_h
        self.clock = pygame.time.Clock()
        self.snowflakes = [Snowflake(self.screen_width, self.screen_height)
                           for _ in range(snow_amount)]
        self.pause = False

    def run(self):
        """
        runs the game loop, and starts the snow

        :return: None
        """
        snowing = True
        while snowing:
            snowing = self.handle_events()

            self.canvas.fill(self.BACKGROUND_COLOR)
            self.wind_speed += random.random() - 0.5

            self.draw_and_move_snowflakes()
            self.refresh_screen()

    def draw_and_move_snowflakes(self):
        """
        iterates over all flakes, and renders them to the screen

        :return: None
        """
        for flake in self.snowflakes:
            pygame.gfxdraw.filled_circle(self.canvas, *flake)
            if not self.pause:
                flake.move(self.wind_speed, self.screen_width, self.screen_height)

    def refresh_screen(self):
        """
        redraw the screen, respects the configured FPS

        :return: None
        """
        pygame.display.update()
        self.clock.tick(self.FPS)

    def handle_events(self):
        """
        handle keypress and external signals
        coming from pygame

        :return: Boolean status telling whether the app is still running or not
        """
        snowing = True
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                snowing = False
            elif event.type == pygame.KEYDOWN:
                if event.key == pygame.K_ESCAPE:
                    snowing = False
                elif event.key == pygame.K_SPACE:
                    self.pause = not self.pause
            elif event.type == pygame.VIDEORESIZE:
                self.screen_width = event.w
                self.screen_height = event.h
        return snowing


def main():
    """
    main invoker for the above classes

    :return: None
    """
    pygame.init()
    screen_mode = pygame.RESIZABLE | pygame.DOUBLEBUF | pygame.SRCALPHA | pygame.HWSURFACE
    screen = pygame.display.set_mode((0, 0), screen_mode, 32)
    app = SnowingApp(screen, snow_amount=4000, wind_speed=25)
    app.run()
    pygame.quit()


if __name__ == "__main__":
    main()