Move with a Scrolling Screen - Margins

Unlike the Move with a Scrolling Screen - Centered which centers the camera on the player, this example only moves the camera if the user gets within so many pixels of the edge. It allows for a ‘box’ in the middle where the user can move around and NOT move the camera.

sprite_move_scrolling_box.py

"""
Scroll around a large screen.

Artwork from https://kenney.nl

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

import random
import arcade

SPRITE_SCALING = 0.5

DEFAULT_SCREEN_WIDTH = 800
DEFAULT_SCREEN_HEIGHT = 600
SCREEN_TITLE = "Sprite Move with Scrolling Screen Example"

# How many pixels to keep as a minimum margin between the character
# and the edge of the screen.
VIEWPORT_MARGIN = 200

# How fast the camera pans to the player. 1.0 is instant.
CAMERA_SPEED = 0.1

# How fast the character moves
PLAYER_MOVEMENT_SPEED = 7


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

    def __init__(self, width, height, title):
        """
        Initializer
        """
        super().__init__(width, height, title, resizable=True)

        # Sprite lists
        self.player_list = None
        self.wall_list = None

        # Set up the player
        self.player_sprite = None

        self.physics_engine = 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.camera_sprites = arcade.camera.Camera2D()
        self.camera_gui = arcade.camera.Camera2D()

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

        # Sprite lists
        self.player_list = arcade.SpriteList()
        self.wall_list = arcade.SpriteList()

        # Set up the player
        self.player_sprite = arcade.Sprite(":resources:images/animated_characters/female_person/femalePerson_idle.png",
                                           scale=0.4)
        self.player_sprite.center_x = 256
        self.player_sprite.center_y = 512
        self.player_list.append(self.player_sprite)

        # -- Set up several columns of walls
        for x in range(200, 1650, 210):
            for y in range(0, 1600, 64):
                # Randomly skip a box so the player can find a way through
                if random.randrange(5) > 0:
                    wall = arcade.Sprite(":resources:images/tiles/grassCenter.png", scale=SPRITE_SCALING)
                    wall.center_x = x
                    wall.center_y = y
                    self.wall_list.append(wall)

        self.physics_engine = arcade.PhysicsEngineSimple(self.player_sprite, self.wall_list)

        # Set the background color
        self.background_color = arcade.color.AMAZON

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

        # This command has to happen before we start drawing
        self.clear()

        # Select the camera we'll use to draw all our sprites
        self.camera_sprites.use()

        # Draw all the sprites.
        self.wall_list.draw()
        self.player_list.draw()

        # Select the (unscrolled) camera for our GUI
        self.camera_gui.use()

        # Draw the GUI
        arcade.draw_rect_filled(arcade.rect.XYWH(self.width // 2, 20, self.width, 40), arcade.color.ALMOND)
        text = f"Scroll value: ({self.camera_sprites.position[0]:5.1f}, {self.camera_sprites.position[1]:5.1f})"
        arcade.draw_text(text, 10, 10, arcade.color.BLACK_BEAN, 20)

        # Draw the box that we work to make sure the user stays inside of.
        # This is just for illustration purposes. You'd want to remove this
        # in your game.
        left_boundary = VIEWPORT_MARGIN
        right_boundary = self.width - VIEWPORT_MARGIN
        top_boundary = self.height - VIEWPORT_MARGIN
        bottom_boundary = VIEWPORT_MARGIN
        arcade.draw_lrbt_rectangle_outline(left_boundary, right_boundary, bottom_boundary, top_boundary,
                                           arcade.color.RED, 2)

    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

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

        # Calculate speed based on the keys pressed
        self.player_sprite.change_x = 0
        self.player_sprite.change_y = 0

        if self.up_pressed and not self.down_pressed:
            self.player_sprite.change_y = PLAYER_MOVEMENT_SPEED
        elif self.down_pressed and not self.up_pressed:
            self.player_sprite.change_y = -PLAYER_MOVEMENT_SPEED
        if self.left_pressed and not self.right_pressed:
            self.player_sprite.change_x = -PLAYER_MOVEMENT_SPEED
        elif self.right_pressed and not self.left_pressed:
            self.player_sprite.change_x = PLAYER_MOVEMENT_SPEED

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

        # Scroll the screen to the player
        self.scroll_to_player()

    def scroll_to_player(self):
        """
        Scroll the window to the player.
        This method will attempt to keep the player at least VIEWPORT_MARGIN
        pixels away from the edge.

        if CAMERA_SPEED is 1, the camera will immediately move to the desired position.
        Anything between 0 and 1 will have the camera move to the location with a smoother
        pan.
        """

        # --- Manage Scrolling ---

        _target_x, _target_y = self.camera_sprites.position

        top_left = self.camera_sprites.top_left
        bottom_right = self.camera_sprites.bottom_right

        # Scroll left
        left_boundary = top_left[0] + VIEWPORT_MARGIN
        if self.player_sprite.left < left_boundary:
            _target_x -= left_boundary - self.player_sprite.left

        # Scroll right
        right_boundary = bottom_right[0] - VIEWPORT_MARGIN
        if self.player_sprite.right > right_boundary:
            _target_x += self.player_sprite.right - right_boundary

        # Scroll up
        top_boundary = top_left[1] - VIEWPORT_MARGIN
        if self.player_sprite.top > top_boundary:
            _target_y += self.player_sprite.top - top_boundary

        # Scroll down
        bottom_boundary = bottom_right[1] + VIEWPORT_MARGIN
        if self.player_sprite.bottom < bottom_boundary:
            _target_y -= bottom_boundary - self.player_sprite.bottom

        # Scroll to the proper location
        position = _target_x, _target_y
        self.camera_sprites.position = arcade.math.lerp_2d(self.camera_sprites.position, position, CAMERA_SPEED)

    def on_resize(self, width: int, height: int):
        """
        Resize window
        Handle the user grabbing the edge and resizing the window.
        """
        super().on_resize(width, height)
        self.camera_sprites.match_screen(and_projection=True)
        self.camera_gui.match_screen(and_projection=True)


def main():
    """ Main function """
    window = MyGame(DEFAULT_SCREEN_WIDTH, DEFAULT_SCREEN_HEIGHT, SCREEN_TITLE)
    window.setup()
    arcade.run()


if __name__ == "__main__":
    main()