Acceleration and Friction¶

sprite_move_keyboard_accel.py
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191``` ```""" Show how to use acceleration and friction 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_accel """ import arcade import os SPRITE_SCALING = 0.5 SCREEN_WIDTH = 800 SCREEN_HEIGHT = 600 SCREEN_TITLE = "Better Move Sprite with Keyboard Example" # Important constants for this example # Speed limit MAX_SPEED = 3.0 # How fast we accelerate ACCELERATION_RATE = 0.1 # How fast to slow down after we letr off the key FRICTION = 0.02 class Player(arcade.Sprite): def update(self): self.center_x += self.change_x self.center_y += self.change_y # Check to see if we hit the screen edge if self.left < 0: self.left = 0 self.change_x = 0 # Zero x speed elif self.right > SCREEN_WIDTH - 1: self.right = SCREEN_WIDTH - 1 self.change_x = 0 if self.bottom < 0: self.bottom = 0 self.change_y = 0 elif self.top > SCREEN_HEIGHT - 1: self.top = SCREEN_HEIGHT - 1 self.change_y = 0 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 # 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. """ # This command has to happen before we start drawing arcade.start_render() # Draw all the sprites. self.player_list.draw() # Display speed arcade.draw_text(f"X Speed: {self.player_sprite.change_x:6.3f}", 10, 50, arcade.color.BLACK) arcade.draw_text(f"Y Speed: {self.player_sprite.change_y:6.3f}", 10, 70, arcade.color.BLACK) def on_update(self, delta_time): """ Movement and game logic """ # Add some friction if self.player_sprite.change_x > FRICTION: self.player_sprite.change_x -= FRICTION elif self.player_sprite.change_x < -FRICTION: self.player_sprite.change_x += FRICTION else: self.player_sprite.change_x = 0 if self.player_sprite.change_y > FRICTION: self.player_sprite.change_y -= FRICTION elif self.player_sprite.change_y < -FRICTION: self.player_sprite.change_y += FRICTION else: self.player_sprite.change_y = 0 # Apply acceleration based on the keys pressed if self.up_pressed and not self.down_pressed: self.player_sprite.change_y += ACCELERATION_RATE elif self.down_pressed and not self.up_pressed: self.player_sprite.change_y += -ACCELERATION_RATE if self.left_pressed and not self.right_pressed: self.player_sprite.change_x += -ACCELERATION_RATE elif self.right_pressed and not self.left_pressed: self.player_sprite.change_x += ACCELERATION_RATE if self.player_sprite.change_x > MAX_SPEED: self.player_sprite.change_x = MAX_SPEED elif self.player_sprite.change_x < -MAX_SPEED: self.player_sprite.change_x = -MAX_SPEED if self.player_sprite.change_y > MAX_SPEED: self.player_sprite.change_y = MAX_SPEED elif self.player_sprite.change_y < -MAX_SPEED: self.player_sprite.change_y = -MAX_SPEED # Call update to move the sprite # If using a physics engine, call update on it instead of the sprite # list. 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 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 main(): """ Main method """ window = MyGame(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_TITLE) window.setup() arcade.run() if __name__ == "__main__": main() ```