In this chapter we will build a shooting game together, step by step.The Python we will use is: conditionals, loops, lists and functions.
10.1. Step 1: Decide what Sprites you will need
Our game will need these Sprites, so we must create images for all ofthem and save them as .png files in the program folder.
variable name | image file name | image size |
|---|---|---|
player | player.png | 64x64 |
background | background.png | 600x800 |
enemies (list) | enemy.png | 64x64 |
bullets (list) | bullet.png | 16x16 |
bombs (list) | bomb.png | 16x16 |
The player and background variables will contain Sprites. Theothers are lists which we initialize to the empty list []. Spriteswill be appended to the lists later.
Program 10.1 Shooter game part 1 of 4
1from rlzero import * 2import random 3 4WIDTH = 600 5HEIGHT = 800 6MAX_BULLETS = 3 7 8level = 1 9lives = 310score = 01112background = Sprite("background.png")13player = Sprite("player.png", (200, 730))14enemies = []15bullets = []16bombs = []
10.2. Step 2: Draw your Sprites
Every RLZero game needs a draw() function, and it should draw allthe Sprites we created above.
Program 10.2 Shooter game part 2 of 4
1def draw(): 2 background.draw() 3 player.draw() 4 for enemy in enemies: 5 enemy.draw() 6 for bullet in bullets: 7 bullet.draw() 8 for bomb in bombs: 9 bomb.draw()10 draw_gui()
10.3. Step 3: Move your Sprites
Every RLZero game needs an update() function to move the Sprites,check for collisions, etc.
Program 10.3 Shooter game part 3 of 4
1def update(delta):2 move_player()3 move_bullets()4 move_enemies()5 create_bombs()6 move_bombs()7 check_for_end_of_level()
10.4. Step 4: Define your functions
Python cannot call a function that has not yet been defined. Thereforewe must at least provide empty, dummy versions of our functions thatdon’t do anything so we can fill them in later. However Python cannotdefine a completely empty function - it must contain at least one line.Therefore we use the pass keyword to create a line that doesn’t doanything.
Program 10.4 Shooter game part 4 of 4
1 2def move_player(): 3 pass 4 5def move_enemies(): 6 pass 7 8def move_bullets(): 9 pass1011def create_bombs():12 pass1314def move_bombs():15 pass1617def check_for_end_of_level():18 pass1920def draw_gui():21 pass2223run()
Exercise
Create the png image files (player.png, background.png, bullet.png, bomb.png, enemy.png). Type in program Program 10.1, Program 10.2 and Program 10.3 and Program 10.4 into a single file. Verify the game now runs and you can see the player at the bottom of the screen. (He can’t move yet.)
10.5. Create enemies
Add this new function to the end of the program, and then call itimmediately. It uses a loop within a loop to create enemy Sprites and putthem in the enemies list. The reason we put this in a function is wewill need to call it again at the start of each level.
def create_enemies(): for x in range(0, 600, 60): for y in range(0, 200, 60): enemy = Sprite("enemy.png", (x, y)) enemy.vx = level * 2 enemies.append(enemy)create_enemies()
10.6. Move the player
Replace the move_player() dummy function definition with this.Remember there can only be one function with a given name. Therecannot be two ``move_player()`` function definitions.
def move_player(): if keyboard.right: player.x = player.x + 5 if keyboard.left: player.x = player.x - 5 if player.x > WIDTH: player.x = WIDTH if player.x < 0: player.x = 0
10.7. Move the enemies
Replace the move_enemies() dummy function definition with this:
def move_enemies(): global score for enemy in enemies: enemy.x = enemy.x + enemy.vx if enemy.x > WIDTH or enemy.x < 0: enemy.vx = -enemy.vx enemy.y += 60 for bullet in bullets: if bullet.colliderect(enemy): enemies.remove(enemy) bullets.remove(bullet) score = score + 1 if enemy.colliderect(player): exit()
10.8. Draw text on the screen
Replace the draw_gui() dummy function definition with this:
def draw_gui(): draw_text("Level " + str(level), 0, 0, 20, RED) draw_text("Score " + str(score), 100, 0, 20, RED) draw_text("Lives " + str(lives), 200, 0, 20, RED)
10.9. Player bullets
Add this new function to the end of the program. Pygame will call it forus automatically when a key is pressed.
def on_key_pressed(key): if key == keys.space and len(bullets) < MAX_BULLETS: bullet = Sprite("bullet.png", pos=(player.x, player.y)) bullets.append(bullet))
Replace the move_bullets() dummy function definition with this:
def move_bullets(): for bullet in bullets: bullet.y = bullet.y - 6 if bullet.y < 0: bullets.remove(bullet)
10.10. Enemy bombs
Replace the create_bombs() dummy function definition with this:
def create_bombs(): if random.randint(0, 100 - level * 6) == 0: enemy = random.choice(enemies) bomb = Sprint("bomb.png", enemy.pos) bombs.append(bomb)
Replace the move_bombs() dummy function definition with this:
def move_bombs(): global lives for bomb in bombs: bomb.y = bomb.y + 10 if bomb.colliderect(player): bombs.remove(bomb) lives = lives - 1 if lives == 0: exit()
10.11. Check for end of level
Replace the check_for_end_of_level() dummy function definition withthis:
def check_for_end_of_level(): global level if len(enemies) == 0: level = level + 1 create_enemies()
10.12. Ideas for extension
Draw an explosion image and create an explosion Sprite every time analien dies.
Make the explosion Sprite disappear after a short time.
Draw several explosion images, put them in a list and make the Spriteanimate displaying each of them in order.
The player can only fire 3 bullets at a time. Create a powerup thatallows him to fire additional bullets.
Add music and sound effects.
