Bloom-Effect Defender

Screen shot of a Defender clone with a bloom/glow effect.

Creating a “glowing” effect can enhance 2D games. This example shows how to do it.

Create Frame Buffer and Post-Processor

Lines 176-202

Here we create the frame buffer, and add a color attachment to store the pixel data into.

It also creates a post-processor that will do a gaussian blur on what is rendered. There are a lot of parameters to the blur, depending on how you want it to look.

Render To Framebuffer

Lines 239-252

When we draw, we render the objects we want to be blurred to our frame buffer, then run the post-processor to do the blur.

Note: This buffer is not transparent! Anything behind it will be hidden. So multiple layers of glow are not possible at this time, nor can you put anything ‘behind’ the glow.

Render Framebuffer To Screen

Lines 264-265

Finally we render that buffer to the screen.

mini_map_defender.py
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"""
Defender Clone.

.. note:: This uses features from the upcoming version 2.4. The API for these
          functions may still change. To use, you will need to install one of the
          pre-release packages, or install via GitHub.

This example shows how to create a 'bloom' or 'glow' effect.

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

import arcade
import os
import random
import pyglet.gl as gl

# --- Bloom related ---
from arcade.experimental import postprocessing

# Size/title of the window
SCREEN_WIDTH = 1280
SCREEN_HEIGHT = 720
SCREEN_TITLE = "Defender Clone"

# Size of the playing field
PLAYING_FIELD_WIDTH = 5000
PLAYING_FIELD_HEIGHT = 1000

# Size of the playing field.
MAIN_SCREEN_HEIGHT = SCREEN_HEIGHT

# How far away from the edges do we get before scrolling?
VIEWPORT_MARGIN = SCREEN_WIDTH / 2 - 50
TOP_VIEWPORT_MARGIN = 30
DEFAULT_BOTTOM_VIEWPORT = -10

# Control the physics of how the player moves
MAX_HORIZONTAL_MOVEMENT_SPEED = 10
MAX_VERTICAL_MOVEMENT_SPEED = 5
HORIZONTAL_ACCELERATION = 0.5
VERTICAL_ACCELERATION = 0.2
MOVEMENT_DRAG = 0.08

# How far the bullet travels before disappearing
BULLET_MAX_DISTANCE = SCREEN_WIDTH * 0.75


class Player(arcade.SpriteSolidColor):
    """ Player ship """
    def __init__(self):
        """ Set up player """
        super().__init__(40, 10, arcade.color.SLATE_GRAY)
        self.face_right = True

    def accelerate_up(self):
        """ Accelerate player up """
        self.change_y += VERTICAL_ACCELERATION
        if self.change_y > MAX_VERTICAL_MOVEMENT_SPEED:
            self.change_y = MAX_VERTICAL_MOVEMENT_SPEED

    def accelerate_down(self):
        """ Accelerate player down """
        self.change_y -= VERTICAL_ACCELERATION
        if self.change_y < -MAX_VERTICAL_MOVEMENT_SPEED:
            self.change_y = -MAX_VERTICAL_MOVEMENT_SPEED

    def accelerate_right(self):
        """ Accelerate player right """
        self.face_right = True
        self.change_x += HORIZONTAL_ACCELERATION
        if self.change_x > MAX_HORIZONTAL_MOVEMENT_SPEED:
            self.change_x = MAX_HORIZONTAL_MOVEMENT_SPEED

    def accelerate_left(self):
        """ Accelerate player left """
        self.face_right = False
        self.change_x -= HORIZONTAL_ACCELERATION
        if self.change_x < -MAX_HORIZONTAL_MOVEMENT_SPEED:
            self.change_x = -MAX_HORIZONTAL_MOVEMENT_SPEED

    def update(self):
        """ Move the player """
        # Move
        self.center_x += self.change_x
        self.center_y += self.change_y

        # Drag
        if self.change_x > 0:
            self.change_x -= MOVEMENT_DRAG
        if self.change_x < 0:
            self.change_x += MOVEMENT_DRAG
        if abs(self.change_x) < MOVEMENT_DRAG:
            self.change_x = 0

        if self.change_y > 0:
            self.change_y -= MOVEMENT_DRAG
        if self.change_y < 0:
            self.change_y += MOVEMENT_DRAG
        if abs(self.change_y) < MOVEMENT_DRAG:
            self.change_y = 0

        # Check bounds
        if self.left < 0:
            self.left = 0
        elif self.right > PLAYING_FIELD_WIDTH - 1:
            self.right = PLAYING_FIELD_WIDTH - 1

        if self.bottom < 0:
            self.bottom = 0
        elif self.top > SCREEN_HEIGHT - 1:
            self.top = SCREEN_HEIGHT - 1

class Bullet(arcade.SpriteSolidColor):
    """ Bullet """

    def __init__(self, width, height, color):
        super().__init__(width, height, color)
        self.distance = 0

    def update(self):
        """ Move the particle, and fade out """
        # Move
        self.center_x += self.change_x
        self.center_y += self.change_y
        self.distance += self.change_x
        if self.distance > BULLET_MAX_DISTANCE:
            self.remove_from_sprite_lists()

class Particle(arcade.SpriteSolidColor):
    """ Particle from explosion """
    def update(self):
        """ Move the particle, and fade out """
        # Move
        self.center_x += self.change_x
        self.center_y += self.change_y
        # Fade
        self.alpha -= 5
        if self.alpha <= 0:
            self.remove_from_sprite_lists()

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

    def __init__(self, width, height, title):
        """ Initializer """

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

        # Set the working directory (where we expect to find files) to the same
        # directory this .py file is in. You can leave this out of your own
        # code, but it is needed to easily run the examples using "python -m"
        # as mentioned at the top of this program.
        file_path = os.path.dirname(os.path.abspath(__file__))
        os.chdir(file_path)

        # Variables that will hold sprite lists
        self.player_list = None
        self.star_sprite_list = None
        self.enemy_sprite_list = None
        self.bullet_sprite_list = None

        # Set up the player info
        self.player_sprite = None

        # Track the current state of what key is pressed
        self.left_pressed = False
        self.right_pressed = False
        self.up_pressed = False
        self.down_pressed = False

        self.view_bottom = 0
        self.view_left = 0

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

        # --- Bloom related ---

        # Frame to receive the glow, and color attachment to store each pixel's
        # color data
        self.bloom_color_attachment = self.ctx.texture((SCREEN_WIDTH, SCREEN_HEIGHT))
        self.bloom_screen = self.ctx.framebuffer(color_attachments=[self.bloom_color_attachment])

        # Down-sampling helps improve the blur.
        # Note: Any item with a size less than the down-sampling size may get missed in
        # the blur process. Down-sampling by 8 and having an item of 4x4 size, the item
        # will get missed 50% of the time in the x direction, and 50% of the time in the
        # y direction for a total of being missed 75% of the time.
        down_sampling = 4
        # Size of the screen we are glowing onto
        size = (SCREEN_WIDTH // down_sampling, SCREEN_HEIGHT // down_sampling)
        # Gaussian blur parameters.
        # To preview different values, see:
        # https://observablehq.com/@jobleonard/gaussian-kernel-calculater
        kernel_size = 21
        sigma = 4
        mu = 0
        step = 1
        # Control the intensity
        multiplier = 2

        # Create a post-processor to create a bloom
        self.bloom_postprocessing = postprocessing.BloomEffect(size, kernel_size, sigma, mu, multiplier, step)

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

        # Sprite lists
        self.player_list = arcade.SpriteList()
        self.star_sprite_list = arcade.SpriteList()
        self.enemy_sprite_list = arcade.SpriteList()
        self.bullet_sprite_list = arcade.SpriteList()

        # Set up the player
        self.player_sprite = Player()
        self.player_sprite.center_x = 50
        self.player_sprite.center_y = 50
        self.player_list.append(self.player_sprite)

        # Add stars
        for i in range(80):
            sprite = arcade.SpriteSolidColor(4, 4, arcade.color.WHITE)
            sprite.center_x = random.randrange(PLAYING_FIELD_WIDTH)
            sprite.center_y = random.randrange(PLAYING_FIELD_HEIGHT)
            self.star_sprite_list.append(sprite)

        # Add enemies
        for i in range(20):
            sprite = arcade.SpriteSolidColor(20, 20, arcade.csscolor.LIGHT_SALMON)
            sprite.center_x = random.randrange(PLAYING_FIELD_WIDTH)
            sprite.center_y = random.randrange(PLAYING_FIELD_HEIGHT)
            self.enemy_sprite_list.append(sprite)

    def on_draw(self):
        """ Render the screen. """
        # This command has to happen before we start drawing
        arcade.start_render()

        # --- Bloom related ---

        # Draw to the 'bloom' layer
        self.bloom_screen.use()
        self.bloom_screen.clear((0, 0, 0, 0))

        arcade.set_viewport(self.view_left,
                            SCREEN_WIDTH + self.view_left,
                            self.view_bottom,
                            SCREEN_HEIGHT + self.view_bottom)

        # Draw all the sprites on the screen that should have a bloom
        self.star_sprite_list.draw()
        self.bullet_sprite_list.draw()

        # Now draw to the actual screen
        self.use()

        arcade.set_viewport(self.view_left,
                            SCREEN_WIDTH + self.view_left,
                            self.view_bottom,
                            SCREEN_HEIGHT + self.view_bottom)

        # --- Bloom related ---

        # Draw the bloom layers
        self.bloom_postprocessing.render(self.bloom_color_attachment, self)

        # Draw the sprites / items that have no bloom
        self.enemy_sprite_list.draw()
        self.player_list.draw()

        # Draw the ground
        arcade.draw_line(0, 0, PLAYING_FIELD_WIDTH, 0, arcade.color.WHITE)

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

        # Calculate speed based on the keys pressed
        if self.up_pressed and not self.down_pressed:
            self.player_sprite.accelerate_up()
        elif self.down_pressed and not self.up_pressed:
            self.player_sprite.accelerate_down()

        if self.left_pressed and not self.right_pressed:
            self.player_sprite.accelerate_left()
        elif self.right_pressed and not self.left_pressed:
            self.player_sprite.accelerate_right()

        # Call update to move the sprite
        self.player_list.update()
        self.bullet_sprite_list.update()

        for bullet in self.bullet_sprite_list:
            enemy_hit_list = arcade.check_for_collision_with_list(bullet, self.enemy_sprite_list)
            for enemy in enemy_hit_list:
                enemy.remove_from_sprite_lists()
                for i in range(10):
                    particle = Particle(4, 4, arcade.color.RED)
                    while particle.change_y == 0 and particle.change_x == 0:
                        particle.change_y = random.randrange(-2, 3)
                        particle.change_x = random.randrange(-2, 3)
                        particle.center_x = enemy.center_x
                        particle.center_y = enemy.center_y
                        self.bullet_sprite_list.append(particle)

        # Scroll left
        left_boundary = self.view_left + VIEWPORT_MARGIN
        if self.player_sprite.left < left_boundary:
            self.view_left -= left_boundary - self.player_sprite.left

        # Scroll right
        right_boundary = self.view_left + SCREEN_WIDTH - VIEWPORT_MARGIN
        if self.player_sprite.right > right_boundary:
            self.view_left += self.player_sprite.right - right_boundary

        # Scroll up
        self.view_bottom = DEFAULT_BOTTOM_VIEWPORT
        top_boundary = self.view_bottom + SCREEN_HEIGHT - TOP_VIEWPORT_MARGIN
        if self.player_sprite.top > top_boundary:
            self.view_bottom += self.player_sprite.top - top_boundary

        self.view_left = int(self.view_left)
        self.view_bottom = int(self.view_bottom)

    def on_key_press(self, key, modifiers):
        """Called whenever a key is pressed. """

        if key == arcade.key.UP:
            self.up_pressed = True
        elif key == arcade.key.DOWN:
            self.down_pressed = True
        elif key == arcade.key.LEFT:
            self.left_pressed = True
        elif key == arcade.key.RIGHT:
            self.right_pressed = True
        elif key == arcade.key.SPACE:
            # Shoot out a bullet/laser
            bullet = arcade.SpriteSolidColor(35, 3, arcade.color.WHITE)
            bullet.center_x = self.player_sprite.center_x
            bullet.center_y = self.player_sprite.center_y
            bullet.change_x = max(12, abs(self.player_sprite.change_x) + 10)

            if not self.player_sprite.face_right:
                bullet.change_x *= -1

            self.bullet_sprite_list.append(bullet)

    def on_key_release(self, key, modifiers):
        """Called when the user releases a key. """

        if key == arcade.key.UP:
            self.up_pressed = False
        elif key == arcade.key.DOWN:
            self.down_pressed = False
        elif key == arcade.key.LEFT:
            self.left_pressed = False
        elif key == arcade.key.RIGHT:
            self.right_pressed = False


def main():
    """ Main method """
    window = MyGame(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_TITLE)
    window.setup()
    arcade.run()


if __name__ == "__main__":
    main()