Asteroids

1. Create a new class called Asteroid in a new file called asteroid.py that inherits from CircleShape.

2. Give it a constructor with this signature, and inside it call the parent CircleShape constructor so the sprite is initialized correctly:

   def __init__(self, x: float, y: float, radius: float) -> None:
       super().__init__(x, y, radius)
   

3. Override the draw() method to draw the asteroid using the pygame.draw.circle function. It accepts:

   • The "surface" to draw on (the screen object)
   • The color of the circle ("white")
   • Its own position as the center
   • Its own radius
   • The width of the line to draw the circle (use LINE_WIDTH from constants.py)

4. Override the update() method so that it moves in a straight line at constant speed. On each frame, it should add (self.velocity * dt) to its position (get self.velocity from its parent class, CircleShape).

5. In main.py before the game loop starts, create a new empty pygame.sprite.Group for the asteroids.

6. Like we did with the Player class, set the static containers field of the Asteroid class to the new asteroids group, as well as the updatable and drawable groups. This ensures that every instance of the Asteroid class is automatically added to these groups upon creation.

   Asteroid.containers = (asteroids, updatable, drawable)
   

7. Add the following constants to constants.py:

   ASTEROID_MIN_RADIUS = 20
   ASTEROID_KINDS = 3
   ASTEROID_SPAWN_RATE_SECONDS = 0.8
   ASTEROID_MAX_RADIUS = ASTEROID_MIN_RADIUS * ASTEROID_KINDS
   

8. I've written an AsteroidField class for you – it contains logic for spawning new asteroids. Create a new file called asteroidfield.py and paste in this code:

   import random
   from collections.abc import Callable
   
   import pygame
   from asteroid import Asteroid
   from constants import *
   
   Edge = tuple[pygame.Vector2, Callable[[float], pygame.Vector2]]
   
   
   class AsteroidField(pygame.sprite.Sprite):
       containers: pygame.sprite.Group
   
       edges: list[Edge] = [
           (
               pygame.Vector2(1, 0),
               lambda y: pygame.Vector2(-ASTEROID_MAX_RADIUS, y * SCREEN_HEIGHT),
           ),
           (
               pygame.Vector2(-1, 0),
               lambda y: pygame.Vector2(
                   SCREEN_WIDTH + ASTEROID_MAX_RADIUS, y * SCREEN_HEIGHT
               ),
           ),
           (
               pygame.Vector2(0, 1),
               lambda x: pygame.Vector2(x * SCREEN_WIDTH, -ASTEROID_MAX_RADIUS),
           ),
           (
               pygame.Vector2(0, -1),
               lambda x: pygame.Vector2(
                   x * SCREEN_WIDTH, SCREEN_HEIGHT + ASTEROID_MAX_RADIUS
               ),
           ),
       ]
   
       def __init__(self) -> None:
           pygame.sprite.Sprite.__init__(self, self.containers)
           self.spawn_timer = 0.0
   
       def spawn(
           self, radius: float, position: pygame.Vector2, velocity: pygame.Vector2
       ) -> None:
           asteroid = Asteroid(position.x, position.y, radius)
           asteroid.velocity = velocity
   
       def update(self, dt: float) -> None:
           self.spawn_timer += dt
           if self.spawn_timer > ASTEROID_SPAWN_RATE_SECONDS:
               self.spawn_timer = 0
   
               # spawn a new asteroid at a random edge
               edge = random.choice(self.edges)
               speed = random.randint(40, 100)
               velocity = edge[0] * speed
               velocity = velocity.rotate(random.randint(-30, 30))
               position = edge[1](random.uniform(0, 1))
               kind = random.randint(1, ASTEROID_KINDS)
               self.spawn(ASTEROID_MIN_RADIUS * kind, position, velocity)
   

9. In the main.py file, import the AsteroidField class and set its static containers field to only the updatable group (it's not drawable, and it's not an asteroid itself).

10. After adding the container, create a new AsteroidField object.

11. Run the game for at least a few seconds, making sure that asteroids are spawning and moving across the screen, and that you didn't break your ship in the process.

If everything looks good, run and submit the CLI tests.