Have Enemies Periodically Shoot

This example uses a variable time_counter that will track how long it has been since we last fired. Each on_update`, we add to that counter the ``delta_time which tracks how long since the method was last called.

Once we get past our trigger point (2 seconds) we reset the timer and fire the bullet.

Screenshot of using sprites to shoot things
sprite_bullets_periodic.py
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"""
Show how to have enemies shoot bullets at regular intervals.

If Python and Arcade are installed, this example can be run from the command line with:
python -m arcade.examples.sprite_bullets_periodic
"""
import arcade

SCREEN_WIDTH = 800
SCREEN_HEIGHT = 600
SCREEN_TITLE = "Sprites and Periodic Bullets Example"


class EnemySprite(arcade.Sprite):
    """ Enemy ship class that tracks how long it has been since firing. """

    def __init__(self, image_file, scale, bullet_list, time_between_firing):
        """ Set up the enemy """
        super().__init__(image_file, scale)

        # How long has it been since we last fired?
        self.time_since_last_firing = 0.0

        # How often do we fire?
        self.time_between_firing = time_between_firing

        # When we fire, what list tracks the bullets?
        self.bullet_list = bullet_list

    def on_update(self, delta_time: float = 1/60):
        """ Update this sprite. """

        # Track time since we last fired
        self.time_since_last_firing += delta_time

        # If we are past the firing time, then fire
        if self.time_since_last_firing >= self.time_between_firing:

            # Reset timer
            self.time_since_last_firing = 0

            # Fire the bullet
            bullet = arcade.Sprite(":resources:images/space_shooter/laserBlue01.png")
            bullet.center_x = self.center_x
            bullet.angle = -90
            bullet.top = self.bottom
            bullet.change_y = -2
            self.bullet_list.append(bullet)


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

    def __init__(self):
        super().__init__(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_TITLE)

        arcade.set_background_color(arcade.color.BLACK)

        self.player = None
        self.player_list = None
        self.enemy_list = None
        self.bullet_list = None

    def setup(self):
        """ Setup the variables for the game. """

        self.player_list = arcade.SpriteList()
        self.enemy_list = arcade.SpriteList()
        self.bullet_list = arcade.SpriteList()

        # Add player ship
        self.player = arcade.Sprite(":resources:images/space_shooter/playerShip1_orange.png", 0.5)
        self.player_list.append(self.player)

        # Add top-left enemy ship
        enemy = EnemySprite(":resources:images/space_shooter/playerShip1_green.png",
                            scale=0.5,
                            bullet_list=self.bullet_list,
                            time_between_firing=2.0)
        enemy.center_x = 120
        enemy.center_y = SCREEN_HEIGHT - enemy.height
        enemy.angle = 180
        self.enemy_list.append(enemy)

        # Add top-right enemy ship
        enemy = EnemySprite(":resources:images/space_shooter/playerShip1_green.png",
                            scale=0.5,
                            bullet_list=self.bullet_list,
                            time_between_firing=1.0)
        enemy.center_x = SCREEN_WIDTH - 120
        enemy.center_y = SCREEN_HEIGHT - enemy.height
        enemy.angle = 180
        self.enemy_list.append(enemy)

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

        arcade.start_render()

        self.enemy_list.draw()
        self.bullet_list.draw()
        self.player_list.draw()

    def on_update(self, delta_time):
        """ All the logic to move, and the game logic goes here. """

        # Call on_update for each enemy in  the list
        self.enemy_list.on_update(delta_time)

        # Get rid of the bullet when it flies off-screen
        for bullet in self.bullet_list:
            if bullet.top < 0:
                bullet.remove_from_sprite_lists()

        self.bullet_list.update()

    def on_mouse_motion(self, x, y, delta_x, delta_y):
        """
        Called whenever the mouse moves.
        """
        self.player.center_x = x
        self.player.center_y = 20


def main():
    """ Run the game """
    window = MyGame()
    window.setup()
    arcade.run()


if __name__ == "__main__":
    main()