11   Sprites

Our games need support for handling objects that collide. Balls bouncing off paddles, laser beams hitting aliens, or our favorite character collecting a coin. All these examples require collision detection.

The Arcade library has support for sprites. A sprite is a two dimensional image that is part of the larger graphical scene. Typically a sprite will be some kind of object in the scene that will be interacted with like a car, frog, or little plumber guy.

../../_images/sprite.png

Originally, video game consoles had built-in hardware support for sprites. Now this specialized hardware support is no longer needed, but we still use the term “sprite.” The history of sprites is interesting, if you want to read up more about it.

11.1   Basic Sprites and Collisions

Let’s step through an example program that uses sprites. This example shows how to create a screen of sprites that are coins, and collect them using a sprite that is a character image controlled by the mouse as shown in the figure below. The program keeps “score” on how many coins have been collected. The code for this example may be found at:

http://arcade.academy/examples/sprite_collect_coins.html

In this chapter, we’ll step through that example.

../../_images/collect_coins.gif

Example Sprite Game

11.1.1   Getting the Application Started

The first few lines of our program start off like other games we’ve done. We import a couple libraries. Set a couple constants for the size of the screen, and a new constant that we will use to scale our graphics to half their original size.

Start of our sprite example
    import random
    import arcade

    SPRITE_SCALING = 0.5

    SCREEN_WIDTH = 800
    SCREEN_HEIGHT = 600


    class MyApplication(arcade.Window):
        # --- Class methods will go here

    window = MyApplication(SCREEN_WIDTH, SCREEN_HEIGHT)
    window.setup()

    arcade.run()

11.1.2   The Constructor

What’s next? We need to add our methods to the MyApplication class. We’ll start with our __init__ method. This is the method we use to initialize our variables. Here it is:

Constructor for MyApplication
def __init__(self, width, height):

    # Call the parent class initializer
    super().__init__(width, height)

    # Variables that will hold sprite lists
    self.all_sprites_list = None
    self.coin_list = None

    # Set up the player info
    self.player_sprite = None
    self.score = 0

    # Don't show the mouse cursor
    self.set_mouse_visible(False)

    # Set the background color
    arcade.set_background_color(arcade.color.AMAZON)

The variables we are creating:

  • all_sprites_list: This is a special list that we will add all our sprites to. By having all the sprites in a single list, we can draw them all in a single command.
  • coin_list: This is a list of all the coins. We wille be checking if the player touches any sprite in this list.
  • player_sprite: This points to our player’s sprite. It is the sprite we will move, and we’ll check to see if it
  • score: This keeps track of our score.

We use a command built into the parent Window class called set_mouse_visible to make the mouse not visible. Finally we set the background color.

11.1.3   The Setup Function

Next up, we have a setup method. In the first code example, we have the code that calls this function near the end: window.setup().

This setup code could be moved into the __init__ method. Why is it separate? Later on if we want to add the ability to “play again”, we can just call the setup function. If the code to set up the window is mixed with the code to set up the game, then it is more difficult to program that functionality. Here we start by keeping them separate.

Setup method for our application
def setup(self):
    """ Set up the game and initialize the variables. """

    # Sprite lists
    self.all_sprites_list = arcade.SpriteList()
    self.coin_list = arcade.SpriteList()

    # Set up the player
    self.score = 0
    self.player_sprite = arcade.Sprite("images/character.png", SPRITE_SCALING)
    self.player_sprite.center_x = 50
    self.player_sprite.center_y = 50
    self.all_sprites_list.append(self.player_sprite)

    for i in range(50):

        # Create the coin instance
        coin = arcade.Sprite("images/coin_01.png", SPRITE_SCALING / 3)

        # Position the coin
        coin.center_x = random.randrange(SCREEN_WIDTH)
        coin.center_y = random.randrange(SCREEN_HEIGHT)

        # Add the coin to the lists
        self.all_sprites_list.append(coin)
        self.coin_list.append(coin)

How does this code work?

First, we need some lists to hold our sprites. We could do something like this:

all_sprites_list = []

But wait! all_sprites_list is an instance variable that’s part of our class. we need to prepend it with self..

self.all_sprites_list = []

However, the Arcade library has a class especially for handling sprite lists. This class is called SpriteList. So instead of creating an empty list with [], we will create a new instance of the SpriteList class:

self.all_sprites_list = SpriteList()

Except that doesn’t work. Why? SpriteList is in the Arcade library. We need to prepend any reference to things in the Arcade library with arcade of course, so now we have:

self.all_sprites_list = arcade.SpriteList()

We need a separate list for just coins. This list won’t have the player. We also need to reset our score to 0.

self.coin_list = arcade.SpriteList()

self.score = 0

Now we need to create out sprite. The name of the class that represents sprites is called Sprite. It takes two paramters. A path to the image we will be using, and how big to scale it.

self.player_sprite = arcade.Sprite("images/character.png", SPRITE_SCALING)

Ok, so if you are following along, you’ll need to download the images. You can right-click on the two images below and save them. The images come from kenney.nl who has a lot of free and cheap game image assets that you can use in your games.

../../_images/character.png

character.png

../../_images/coin_01.png

coin_01.png

Where should you save them? It depends. If you load your sprite with the code below, the computer will look for the character.png image in the same directory as your Python file. Save the image anywhere else, and it won’t be found.

self.player_sprite = arcade.Sprite("character.png", SPRITE_SCALING)

I don’t like putting my images with my code. By the time I finish a game there’s a lot of images, sounds, and other files all mixed together. Instead I like to create subdirectories for images and sounds. You can do this by creating a subdirectory called “images” and them prepending “images/” to your filename.

self.player_sprite = arcade.Sprite("images/character.png", SPRITE_SCALING)

11.1.4   The On Draw Method

How do we draw all our sprites? Really easy. We just override the on_draw method and call the draw method in our sprites list. That method will loop throug all our sprites for us, and draw them.

def on_draw(self):

        arcade.start_render()

        # Draw all the sprites.
        self.all_sprites_list.draw()

Woohoo! That was easy.

In addition to drawing the sprites, let’s go ahead and put the score on the screen:

# Put the text on the screen.
output = "Score: " + str(self.score)
arcade.draw_text(output, 10, 20, arcade.color.WHITE, 14)

Rather than do that "Score: " + str(self.score) it is possible to do print formatting if you are using Python 3.6 or later. We’ll talk more about print formatting later, but that code would look like:

# Put the text on the screen.
output = f"Score: {self.score}"
arcade.draw_text(output, 10, 20, arcade.color.WHITE, 14)

There are three standards for how to format strings in Python, so that whole subject is a bit confusing.

11.1.5   The On Mouse Motion Method

Moving the player sprite with the mouse is easy. All sprites have instance variables center_x and center_y. Just change those values to the mouse’s x and y location to move the sprite.

def on_mouse_motion(self, x, y, dx, dy):

    self.player_sprite.center_x = x
    self.player_sprite.center_y = y

11.1.6   The Animate Method

Our animate method needs to do three things:

  1. Update the sprites
  2. Check to see if the player is touching any coins
  3. Remove any coins colliding with the player, and update the score.

Each sprite has its own update method. This allows sprites to move and animate its images. Right now, our sprite does not have this method. But we will soon. Rather than call the update method of each sprite we have, there is an update method in each sprite list that will call update on each sprite in the list. Therefore, just calling update with our all_sprites_list will cause all sprites to update.

self.all_sprites_list.update()

How do we detect what coins are touching the player? We call the check_for_collision_with_list method. Pass it in our player sprite, along with a list of all the coins. That function will return a list of all colliding sprites. If no sprites collide, the list will be empty.

# Generate a list of all sprites that collided with the player.
hit_list = arcade.check_for_collision_with_list(self.player_sprite,
                                                self.coin_list)

What do we do with this hit_list we get back? We loop through it. We add one to the score for each sprite hit.

We also need to get rid of the sprite. The sprite class has a method called kill. This method will remove the sprite from existance.

# Loop through each colliding sprite, remove it, and add to the score.
for coin in hit_list:
    coin.kill()
    self.score += 1

Here’s the whole animate method put together:

def animate(self, delta_time):
    """ Movement and game logic """

    # Call update on all sprites (The sprites don't do much in this
    # example though.)
    self.all_sprites_list.update()

    # Generate a list of all sprites that collided with the player.
    hit_list = arcade.check_for_collision_with_list(self.player_sprite,
                                                    self.coin_list)

    # Loop through each colliding sprite, remove it, and add to the score.
    for coin in hit_list:
        coin.kill()
        self.score += 1

11.2   Moving Sprites

How do we get sprites to move? Start the code from our original example here:

http://arcade.academy/examples/sprite_collect_coins.html

To customize our sprite’s behavior, we need to subclass the Sprite class with our own child class. This is easy:

class Coin(arcade.Sprite):

We need to provide each sprite with a update method. The update method is automatically called to update the sprite’s position.

class Coin(arcade.Sprite):

    def update(self):
        # Code to move goes here

Wait! We have a new class called Coin, but we aren’t using it. Find in our original code this line:

coin = arcade.Sprite("images/coin_01.png", SPRITE_SCALING / 3)

See how it is creating an instance of Sprite? We want to create an instance of our new Coin class instead:

coin = Coin("images/coin_01.png", SPRITE_SCALING / 3)

Now, how do we get the coin to move?

11.2.1   Moving Sprites Down

To get the sprites to “fall” down the screen, we need to make their y location smaller. This is easy. Over-ride update in the sprite and subtract from y each frame:

class Coin(arcade.Sprite):

    def update(self):
        self.center_y -= 1

This causes the coins to move down. But once they move off the screen they keep going into negative-coordinate land. We can’t see them any more. Sad.

../../_images/coins_down_1.gif

Coins moving down

We can get around this by resetting the coins up to the top. Here’s how its done:

class Coin(arcade.Sprite):

    def update(self):
        self.center_y -= 1

        # See if we went off-screen
        if self.center_y < 0:
            self.center_y = SCREEN_HEIGHT

But this isn’t perfect. Because if your eyes are fast, you can see the coin ‘pop’ in and out of existence at the edge. It doesn’t smoothly slide off. This is because we move it when the center of the coin is at the edge. Not the top of the coin has slid off.

There are a couple ways we can do this. Here’s one. We’ll check at -20 instead of 0. As long as the coin radius is 20 or less, we are good.

class Coin(arcade.Sprite):

    def update(self):
        self.center_y -= 1

        # See if we went off-screen
        if self.center_y < -20:
            self.center_y = SCREEN_HEIGHT + 20

There’s another way. In addition to center_y, sprites have other members that are useful in these cases. They are top, bottom, left and right. So we can do this:

class Coin(arcade.Sprite):

    def update(self):
        self.center_y -= 1

        # See if we went off-screen
        if self.top < 0:
            self.bottom = SCREEN_HEIGHT

Doing this allows the coins to smoothly slide on and off the screen. But since they reappear at the top, we get repeating patters. See the image below:

../../_images/pattern.gif

Coins repeating in a pattern

Instead we can randomize it a bit:

def update(self):

    # Move the coin
    self.center_y -= 1

    # See if the coin has fallen off the bottom of the screen.
    # If so, reset it.
    if self.top < 0:
        # Reset the coin to a random spot above the screen
        self.center_y = random.randrange(SCREEN_HEIGHT + 20,
                                         SCREEN_HEIGHT + 100)
        self.center_x = random.randrange(SCREEN_WIDTH)

This works, but when we we collect all the coins we are done. What if it was a never-ending set of coins? Instead of “killing” the coin, let’s reset it to the top of the screen.

def animate(self, delta_time):
    """ Movement and game logic """

    self.all_sprites_list.update()

    hit_list = arcade.check_for_collision_with_list(self.player_sprite, self.coin_list)

    for coin in hit_list:
        self.score += 1

        # Reset the coin to a random spot above the screen
        coin.center_y = random.randrange(SCREEN_HEIGHT + 20,
                                         SCREEN_HEIGHT + 100)
        coin.center_x = random.randrange(SCREEN_WIDTH)

We can even take that common code, and move it to a method. Here’s a full example:

sprites_move_down.py
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import random
import arcade

SPRITE_SCALING = 0.5

SCREEN_WIDTH = 800
SCREEN_HEIGHT = 600


class Coin(arcade.Sprite):
    """
    This class represents the coins on our screen. It is a child class of
    the arcade library's "Sprite" class.
    """

    def reset_pos(self):

        # Reset the coin to a random spot above the screen
        self.center_y = random.randrange(SCREEN_HEIGHT + 20,
                                         SCREEN_HEIGHT + 100)
        self.center_x = random.randrange(SCREEN_WIDTH)

    def update(self):

        # Move the coin
        self.center_y -= 1

        # See if the coin has fallen off the bottom of the screen.
        # If so, reset it.
        if self.top < 0:
            self.reset_pos()


class MyAppWindow(arcade.Window):
    """ Main application class. """

    def __init__(self, width, height):
        """
        Initializer
        :param width:
        :param height:
        """
        super().__init__(width, height)
        # Sprite lists
        self.all_sprites_list = None
        self.coin_list = None

        # Set up the player
        self.score = 0
        self.player_sprite = None

    def start_new_game(self):
        """ Set up the game and initialize the variables. """

        # Sprite lists
        self.all_sprites_list = arcade.SpriteList()
        self.coin_list = arcade.SpriteList()

        # Set up the player
        self.score = 0
        self.player_sprite = arcade.Sprite("character.png",
                                           SPRITE_SCALING)
        self.player_sprite.center_x = 50
        self.player_sprite.center_y = 70
        self.all_sprites_list.append(self.player_sprite)

        for i in range(50):

            # Create the coin instance
            coin = Coin("coin_01.png", SPRITE_SCALING / 3)

            # Position the coin
            coin.center_x = random.randrange(SCREEN_WIDTH)
            coin.center_y = random.randrange(SCREEN_HEIGHT)

            # Add the coin to the lists
            self.all_sprites_list.append(coin)
            self.coin_list.append(coin)

        # Don't show the mouse cursor
        self.set_mouse_visible(False)

        # Set the background color
        arcade.set_background_color(arcade.color.AMAZON)

    def on_draw(self):
        """
        Render the screen.
        """

        # This command has to happen before we start drawing
        arcade.start_render()

        # Draw all the sprites.
        self.all_sprites_list.draw()

        # Put the text on the screen.
        output = "Score: {}".format(self.score)
        arcade.draw_text(output, 10, 20, arcade.color.WHITE, 14)

    def on_mouse_motion(self, x, y, dx, dy):
        """
        Called whenever the mouse moves.
        """
        self.player_sprite.center_x = x
        self.player_sprite.center_y = y

    def animate(self, delta_time):
        """ Movement and game logic """

        # Call update on all sprites (The sprites don't do much in this
        # example though.)
        self.all_sprites_list.update()

        # Generate a list of all sprites that collided with the player.
        hit_list = arcade.check_for_collision_with_list(self.player_sprite,
                                                        self.coin_list)

        # Loop through each colliding sprite, remove it, and add to the score.
        for coin in hit_list:
            coin.reset_pos()
            self.score += 1


def main():
    window = MyAppWindow(SCREEN_WIDTH, SCREEN_HEIGHT)
    window.start_new_game()
    arcade.run()


if __name__ == "__main__":
    main()

11.2.2   Bouncing

../../_images/sprites_bouncing.gif

Coins bouncing around

sprites_bouncing.py
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import random
import arcade

SPRITE_SCALING = 0.5

SCREEN_WIDTH = 800
SCREEN_HEIGHT = 600


class Coin(arcade.Sprite):

    def __init__(self, filename, sprite_scaling):

        super().__init__(filename, sprite_scaling)

        self.change_x = 0
        self.change_y = 0

    def update(self):

        # Move the coin
        self.center_x += self.change_x
        self.center_y += self.change_y

        # If we are out-of-bounds, then 'bounce'
        if self.left < 0:
            self.change_x *= -1

        if self.right > SCREEN_WIDTH:
            self.change_x *= -1

        if self.bottom < 0:
            self.change_y *= -1

        if self.top > SCREEN_HEIGHT:
            self.change_y *= -1


class MyAppWindow(arcade.Window):
    """ Main application class. """

    def __init__(self, width, height):

        super().__init__(width, height)
        # Sprite lists
        self.all_sprites_list = None
        self.coin_list = None

        # Set up the player
        self.score = 0
        self.player_sprite = None

    def start_new_game(self):
        """ Set up the game and initialize the variables. """

        # Sprite lists
        self.all_sprites_list = arcade.SpriteList()
        self.coin_list = arcade.SpriteList()

        # Set up the player
        self.score = 0
        self.player_sprite = arcade.Sprite("character.png",
                                           SPRITE_SCALING)
        self.player_sprite.center_x = 50
        self.player_sprite.center_y = 70
        self.all_sprites_list.append(self.player_sprite)

        for i in range(50):

            # Create the coin instance
            coin = Coin("coin_01.png", SPRITE_SCALING / 3)

            # Position the coin
            coin.center_x = random.randrange(SCREEN_WIDTH)
            coin.center_y = random.randrange(SCREEN_HEIGHT)
            coin.change_x = random.randrange(-3, 4)
            coin.change_y = random.randrange(-3, 4)

            # Add the coin to the lists
            self.all_sprites_list.append(coin)
            self.coin_list.append(coin)

        # Don't show the mouse cursor
        self.set_mouse_visible(False)

        # Set the background color
        arcade.set_background_color(arcade.color.AMAZON)

    def on_draw(self):

        # This command has to happen before we start drawing
        arcade.start_render()

        # Draw all the sprites.
        self.all_sprites_list.draw()

        # Put the text on the screen.
        output = "Score: " + str(self.score)
        arcade.draw_text(output, 10, 20, arcade.color.WHITE, 14)

    def on_mouse_motion(self, x, y, dx, dy):
        self.player_sprite.center_x = x
        self.player_sprite.center_y = y

    def animate(self, delta_time):
        """ Movement and game logic """

        # Call update on all sprites (The sprites don't do much in this
        # example though.)
        self.all_sprites_list.update()

        # Generate a list of all sprites that collided with the player.
        hit_list = arcade.check_for_collision_with_list(self.player_sprite,
                                                        self.coin_list)

        # Loop through each colliding sprite, remove it, and add to the score.
        for coin in hit_list:
            self.score += 1
            coin.kill()

def main():
    window = MyAppWindow(SCREEN_WIDTH, SCREEN_HEIGHT)
    window.start_new_game()
    arcade.run()


if __name__ == "__main__":
    main()

Take what you’ve learned from the example above, and see if you can replicate this:

../../_images/Test_Pattern.gif

Test Pattern

11.2.3   Circles

../../_images/sprites_circle.gif

Coins moving in a circle

sprites_circle.py
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import random
import arcade
import math

SPRITE_SCALING = 0.5

SCREEN_WIDTH = 800
SCREEN_HEIGHT = 600


class Coin(arcade.Sprite):

    def __init__(self, filename, sprite_scaling):
        """ Constructor. """
        # Call the parent class (Sprite) constructor
        super().__init__(filename, sprite_scaling)

        # Current angle in radians
        self.angle = 0

        # How far away from the center to orbit, in pixels
        self.radius = 0

        # How fast to orbit, in radians per frame
        self.speed = 0.008

        # Set the center of the point we will orbit around
        self.circle_center_x = 0
        self.circle_center_y = 0

    def update(self):

        """ Update the ball's position. """
        # Calculate a new x, y
        self.center_x = self.radius * math.sin(self.angle) \
            + self.circle_center_x
        self.center_y = self.radius * math.cos(self.angle) \
            + self.circle_center_y

        # Increase the angle in prep for the next round.
        self.angle += self.speed


class MyAppWindow(arcade.Window):
    """ Main application class. """

    def __init__(self, width, height):

        super().__init__(width, height)
        # Sprite lists
        self.all_sprites_list = None
        self.coin_list = None

        # Set up the player
        self.score = 0
        self.player_sprite = None

    def start_new_game(self):
        """ Set up the game and initialize the variables. """

        # Sprite lists
        self.all_sprites_list = arcade.SpriteList()
        self.coin_list = arcade.SpriteList()

        # Set up the player
        self.score = 0
        self.player_sprite = arcade.Sprite("character.png",
                                           SPRITE_SCALING)
        self.player_sprite.center_x = 50
        self.player_sprite.center_y = 70
        self.all_sprites_list.append(self.player_sprite)

        for i in range(50):

            # Create the coin instance
            coin = Coin("coin_01.png", SPRITE_SCALING / 3)

            # Position the center of the circle the coin will orbit
            coin.circle_center_x = random.randrange(SCREEN_WIDTH)
            coin.circle_center_y = random.randrange(SCREEN_HEIGHT)

            # Random radius from 10 to 200
            coin.radius = random.randrange(10, 200)

            # Random start angle from 0 to 2pi
            coin.angle = random.random() * 2 * math.pi

            # Add the coin to the lists
            self.all_sprites_list.append(coin)
            self.coin_list.append(coin)

        # Don't show the mouse cursor
        self.set_mouse_visible(False)

        # Set the background color
        arcade.set_background_color(arcade.color.AMAZON)

    def on_draw(self):

        # This command has to happen before we start drawing
        arcade.start_render()

        # Draw all the sprites.
        self.all_sprites_list.draw()

        # Put the text on the screen.
        output = "Score: " + str(self.score)
        arcade.draw_text(output, 10, 20, arcade.color.WHITE, 14)

    def on_mouse_motion(self, x, y, dx, dy):
        self.player_sprite.center_x = x
        self.player_sprite.center_y = y

    def animate(self, delta_time):
        """ Movement and game logic """

        # Call update on all sprites (The sprites don't do much in this
        # example though.)
        self.all_sprites_list.update()

        # Generate a list of all sprites that collided with the player.
        hit_list = arcade.check_for_collision_with_list(self.player_sprite,
                                                        self.coin_list)

        # Loop through each colliding sprite, remove it, and add to the score.
        for coin in hit_list:
            self.score += 1
            coin.kill()

def main():
    window = MyAppWindow(SCREEN_WIDTH, SCREEN_HEIGHT)
    window.start_new_game()
    arcade.run()


if __name__ == "__main__":
    main()

11.3   Rotating Sprites

Sprites can easily be rotated by setting their angle attribute. Angles are in degrees. So the following will flip the player upside down:

self.player_sprite.angle = 180

If you put this in the coin’s animate method, it would cause the coins to spin:

self.angle += 1

# If we rotate past 360, reset it back a turn.
if self.angle > 359:
    self.angle -= 360

11.4   Using Sprites to Shoot

How do we get sprites that we can shoot?

First, we need a ‘shooting’ image:

../../_images/laserBlue01.png

laserBlue01.png

../../_images/sprites_bullet.gif

Coins shooting

To start with, we need a sprite to represent the bullet. It will be a moving sprite:

class Bullet(arcade.Sprite):
    def update(self):
        self.center_y += BULLET_SPEED

This gets the bullets to move up. But we don’t have any bullets. We need to create bullets when the user presses the mouse button. We can add an on_mouse_press method to do something when the user presses the mouse button:

def on_mouse_press(self, x, y, button, modifiers):

    # Create a bullet
    bullet = Bullet("laserBlue01.png", SPRITE_SCALING * 1.5)

    # The image points to the right, and we want it to point up. So
    # rotate it.
    bullet.angle = 90

    # Position the bullet
    bullet.center_x = self.player_sprite.center_x
    bullet.bottom = self.player_sprite.top

    # Add the bullet to the appropriate lists
    self.all_sprites_list.append(bullet)
    self.bullet_list.append(bullet)

The two key points with the code above is that 1.) We position the bullet right above the player that spawned it:

bullet.center_x = self.player_sprite.center_x
bullet.bottom = self.player_sprite.top

And two, we can rotate a sprite! Since the bullet image has the bullet going sideways, that’s no good. There is an attribute with any sprite that you can set called angle. So we just set the angle to 90 to rotate it.

bullet.angle = 90

Now that we have bullets, how do we get them to collide with the coins? We add the following to our applications animate method:

# Loop through each bullet
for bullet in self.bullet_list:

    # Check this bullet to see if it hit a coin
    hit_list = arcade.check_for_collision_with_list(bullet,
                                                    self.coin_list)

    # If it did, get rid of the bullet
    if len(hit_list) > 0:
        bullet.kill()

    # For every coin we hit, add to the score and remove the coin
    for coin in hit_list:
        coin.kill()
        self.score += 1

    # If the bullet flies off-screen, remove it.
    if bullet.bottom > SCREEN_HEIGHT:
        bullet.kill()

We loop through each bullet with a for loop. Then we check to see if the bullet is hitting any of the coins. If it is, we get rid of the coin. We get rid of the bullet.

We also check to see if the bullet flies off the top of the screen. If it does, we get rid of the bullet. This is easy to forget, but if you do, it will cause the computer to slow down because you are tracking thousands of bullets that have long ago left the space we care about.

Here’s the full example:

sprites_bullet.py
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import random
import arcade

SPRITE_SCALING = 0.5

SCREEN_WIDTH = 800
SCREEN_HEIGHT = 600

BULLET_SPEED = 5


class Bullet(arcade.Sprite):
    def update(self):
        self.center_y += BULLET_SPEED


class MyAppWindow(arcade.Window):
    """ Main application class. """

    def __init__(self):
        super().__init__(SCREEN_WIDTH, SCREEN_HEIGHT, "Sprites and Bullets Demo")

        """ Set up the game and initialize the variables. """

        # Sprite lists
        self.all_sprites_list = arcade.SpriteList()
        self.coin_list = arcade.SpriteList()
        self.bullet_list = arcade.SpriteList()

        # Set up the player
        self.score = 0
        self.player_sprite = arcade.Sprite("character.png", SPRITE_SCALING)
        self.player_sprite.center_x = 50
        self.player_sprite.center_y = 70
        self.all_sprites_list.append(self.player_sprite)

        for i in range(50):

            # Create the coin instance
            coin = arcade.Sprite("coin_01.png", SPRITE_SCALING / 3)

            # Position the coin
            coin.center_x = random.randrange(SCREEN_WIDTH)
            coin.center_y = random.randrange(120, SCREEN_HEIGHT)

            # Add the coin to the lists
            self.all_sprites_list.append(coin)
            self.coin_list.append(coin)

        # Don't show the mouse cursor
        self.set_mouse_visible(False)

        # Set the background color
        arcade.set_background_color(arcade.color.AMAZON)

    def on_draw(self):

        arcade.start_render()

        # Draw all the sprites.
        self.all_sprites_list.draw()

        # Put the text on the screen.
        output = "Score: " + str(self.score)
        arcade.draw_text(output, 10, 20, arcade.color.WHITE, 14)

    def on_mouse_motion(self, x, y, dx, dy):
        self.player_sprite.center_x = x

    def on_mouse_press(self, x, y, button, modifiers):

        # Create a bullet
        bullet = Bullet("laserBlue01.png", SPRITE_SCALING * 1.5)

        # The image points to the right, and we want it to point up. So
        # rotate it.
        bullet.angle = 90

        # Position the bullet
        bullet.center_x = self.player_sprite.center_x
        bullet.bottom = self.player_sprite.top

        # Add the bullet to the appropriate lists
        self.all_sprites_list.append(bullet)
        self.bullet_list.append(bullet)

    def animate(self, delta_time):
        """ Movement and game logic """

        # Call update on all sprites (The sprites don't do much in this
        # example though.)
        self.all_sprites_list.update()

        # Loop through each bullet
        for bullet in self.bullet_list:

            # Check this bullet to see if it hit a coin
            hit_list = arcade.check_for_collision_with_list(bullet,
                                                            self.coin_list)

            # If it did, get rid of the bullet
            if len(hit_list) > 0:
                bullet.kill()

            # For every coin we hit, add to the score and remove the coin
            for coin in hit_list:
                coin.kill()
                self.score += 1

            # If the bullet flies off-screen, remove it.
            if bullet.bottom > SCREEN_HEIGHT:
                bullet.kill()


def main():
    MyAppWindow()
    arcade.run()


if __name__ == "__main__":
    main()