Asteroids Spaceship

Surprisingly, learning about physics and trigonometry is fun with Pygame. I wrote this to learn how to add vectors and simulate the type of movement from Atari’s Asteroid. One vector is the trajectory of the spaceship. When thrust is applied, another vector is added: the direction that the spaceship is pointing (not the direction the spaceship is moving) and thrust is applied.

Here is the code. I didn’t get a chance to clean it up or add comments.

import pygame
import math
import random

pygame.init()
screen = pygame.display.set_mode((700, 700))

white   = (255, 255, 255)
black   = (000, 000, 000)
red     = (255, 000, 000)

clock = pygame.time.Clock()

running = True

def addVectors((angle1, length1), (angle2, length2)):
    x  = math.sin(angle1) * length1 + math.sin(angle2) * length2
    y  = math.cos(angle1) * length1 + math.cos(angle2) * length2
    
    angle = 0.5 * math.pi - math.atan2(y, x)
    length  = math.hypot(x, y)

    return (angle, length)

def draw_spaceship(x, y, angle):
    magnitude = 30
    p1_angle = angle
    p2_angle = angle + math.radians(145)
    p3_angle = angle - math.radians(145)
    p1 = (math.cos(p1_angle) * magnitude + x, -math.sin(p1_angle) * magnitude + y)
    p2 = (math.cos(p2_angle) * magnitude + x, -math.sin(p2_angle) * magnitude + y)
    p3 = (math.cos(p3_angle) * magnitude + x, -math.sin(p3_angle) * magnitude + y)

    pygame.draw.line(screen, white, (p1[0], p1[1]), (p2[0], p2[1]))
    pygame.draw.line(screen, white, (p1[0], p1[1]), (p3[0], p3[1]))
    pygame.draw.line(screen, white, (p2[0], p2[1]), (p3[0], p3[1]))


angle = math.pi / 2
angle_change = 0
trajectory_angle = angle

x, y = 350, 350

speed = 0
thrust = 0
max_speed = 8

stars = [(random.randint(0, 699), random.randint(0, 699)) for x in range(140)]

bullet_speed = 5

bullets = []

while running:

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                angle_change = .03
            elif event.key == pygame.K_RIGHT:
                angle_change = -.03
            elif event.key == pygame.K_UP:
                thrust = .08
            elif event.key == pygame.K_SPACE:
                bullet_angle = angle
                # adjust the position of the bullet so that it is comming
                # from the front point of the ship
                offset_bullet_x = x + math.cos(bullet_angle) * 30
                offset_bullet_y = y + -math.sin(bullet_angle) * 30
                bullets.append([bullet_angle, offset_bullet_x, offset_bullet_y])
        if event.type == pygame.KEYUP:
            if event.key == pygame.K_LEFT:
                angle_change = 0
            elif event.key == pygame.K_RIGHT:
                angle_change = 0
            elif event.key == pygame.K_UP:
                thrust = 0


    screen.fill(black)

    
    for b in bullets:
        bullet_angle = b[0]
        bullet_x = b[1]
        bullet_y = b[2]
        bullet_x_offset = math.cos(bullet_angle) * 4
        bullet_y_offset = -math.sin(bullet_angle) * 4

        pygame.draw.line(screen,
                (255, 0, 0),
                (bullet_x, bullet_y),
                (int(bullet_x + bullet_x_offset), int(bullet_y + bullet_y_offset)),
                2
            )

        b[1] += math.cos(bullet_angle) * bullet_speed
        b[2] -= math.sin(bullet_angle) * bullet_speed
        if b[1] > 700 or b[2] > 700 or b[1] < 0 or b[2] < 0:
            bullets.remove(b)

    for star in stars:
        star_x, star_y = star[0], star[1]
        pygame.draw.line(screen, white, (star_x, star_y), (star_x, star_y))

    angle += angle_change

    trajectory_angle, speed = addVectors((trajectory_angle, speed), (angle,
        thrust))

    if speed > max_speed:
        speed = max_speed
    x += math.cos(trajectory_angle) * speed
    y -= math.sin(trajectory_angle) * speed

    x %= 760
    y %= 760

    draw_spaceship(x, y, angle)

    pygame.display.flip()

    clock.tick(90)

pygame.quit()

Paul Mouzas

Asteroids Spaceship