Better Move By Keyboard#

Screen shot of moving a sprite by keyboard

If a player presses the left key, the sprite should move left. If the player hits both left and right, the player should stop. If the player lets off the left key, keeping the right key down, the player should move right.

The simpler method of handling keystrokes will not handle this correctly. This code tracks which key is down or up, and handles it properly.

See the highlighted sections.

sprite_move_keyboard_better.py#
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"""
Better Move Sprite With Keyboard

Simple program to show moving a sprite with the keyboard.
This is slightly better than sprite_move_keyboard.py example
in how it works, but also slightly more complex.

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_keyboard_better
"""

import arcade

SPRITE_SCALING = 0.5

SCREEN_WIDTH = 800
SCREEN_HEIGHT = 600
SCREEN_TITLE = "Better Move Sprite with Keyboard Example"

MOVEMENT_SPEED = 5


class Player(arcade.Sprite):

    def update(self):
        """ Move the player """
        # Move player.
        # Remove these lines if physics engine is moving player.
        self.center_x += self.change_x
        self.center_y += self.change_y

        # Check for out-of-bounds
        if self.left < 0:
            self.left = 0
        elif self.right > SCREEN_WIDTH - 1:
            self.right = SCREEN_WIDTH - 1

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


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

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

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

        # Variables that will hold sprite lists
        self.player_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

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

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

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

        # Set up the player
        self.player_sprite = Player(":resources:images/animated_characters/female_person/femalePerson_idle.png",
                                    SPRITE_SCALING)
        self.player_sprite.center_x = 50
        self.player_sprite.center_y = 50
        self.player_list.append(self.player_sprite)

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

        # Clear the screen
        self.clear()

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

    def update_player_speed(self):

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

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

        # Call update to move the sprite
        # If using a physics engine, call update player to rely on physics engine
        # for movement, and call physics engine here.
        self.player_list.update()

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

        if key == arcade.key.UP:
            self.up_pressed = True
            self.update_player_speed()
        elif key == arcade.key.DOWN:
            self.down_pressed = True
            self.update_player_speed()
        elif key == arcade.key.LEFT:
            self.left_pressed = True
            self.update_player_speed()
        elif key == arcade.key.RIGHT:
            self.right_pressed = True
            self.update_player_speed()

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

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


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


if __name__ == "__main__":
    main()