# A-Star Path Finding#

## Explanation#

A-star path finding can be used to find a way to go from one spot to another around barriers. This example just draws the path, based on the coordinates returned. If you want the enemy to follow that path, see Sprites That Follow a Path.

## Source#

astar_pathfinding.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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264``` ```""" A-Star Path-finding 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.astar_pathfinding """ import arcade import random SPRITE_IMAGE_SIZE = 128 SPRITE_SCALING = 0.25 SPRITE_SIZE = int(SPRITE_IMAGE_SIZE * SPRITE_SCALING) SCREEN_WIDTH = 800 SCREEN_HEIGHT = 600 SCREEN_TITLE = "A-Star Path-finding" MOVEMENT_SPEED = 5 VIEWPORT_MARGIN = 100 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 self.wall_list = None self.enemy_list = None # Set up the player info self.player = 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.physics_engine = None # --- Related to paths # List of points that makes up a path between two points self.path = None # List of points we checked to see if there is a barrier there self.barrier_list = None # Used in scrolling self.view_bottom = 0 self.view_left = 0 # Set the window background color self.background_color = arcade.color.AMAZON def setup(self): """ Set up the game and initialize the variables. """ # Sprite lists self.player_list = arcade.SpriteList() self.wall_list = arcade.SpriteList(use_spatial_hash=True, spatial_hash_cell_size=128) self.enemy_list = arcade.SpriteList() # Set up the player resource = ":resources:images/animated_characters/" \ "female_person/femalePerson_idle.png" self.player = arcade.Sprite(resource, SPRITE_SCALING) self.player.center_x = SPRITE_SIZE * 5 self.player.center_y = SPRITE_SIZE * 1 self.player_list.append(self.player) # Set enemies resource = ":resources:images/animated_characters/zombie/zombie_idle.png" enemy = arcade.Sprite(resource, SPRITE_SCALING) enemy.center_x = SPRITE_SIZE * 4 enemy.center_y = SPRITE_SIZE * 7 self.enemy_list.append(enemy) spacing = SPRITE_SIZE * 3 for column in range(10): for row in range(15): sprite = arcade.Sprite(":resources:images/tiles/grassCenter.png", SPRITE_SCALING) x = (column + 1) * spacing y = (row + 1) * sprite.height sprite.center_x = x sprite.center_y = y if random.randrange(100) > 30: self.wall_list.append(sprite) self.physics_engine = arcade.PhysicsEngineSimple(self.player, self.wall_list) # --- Path related # This variable holds the travel-path. We keep it as an attribute so # we can calculate it in on_update, and draw it in on_draw. self.path = None # Grid size for calculations. The smaller the grid, the longer the time # for calculations. Make sure the grid aligns with the sprite wall grid, # or some openings might be missed. grid_size = SPRITE_SIZE # Calculate the playing field size. We can't generate paths outside of # this. playing_field_left_boundary = -SPRITE_SIZE * 2 playing_field_right_boundary = SPRITE_SIZE * 35 playing_field_top_boundary = SPRITE_SIZE * 17 playing_field_bottom_boundary = -SPRITE_SIZE * 2 # This calculates a list of barriers. By calculating it here in the # init, we are assuming this list does not change. In this example, # our walls don't move, so that is ok. If we want moving barriers (such as # moving platforms or enemies) we need to recalculate. This can be an # time-intensive process depending on the playing field size and grid # resolution. # Note: If the enemy sprites are the same size, we only need to calculate # one of these. We do NOT need a different one for each enemy. The sprite # is just used for a size calculation. self.barrier_list = arcade.AStarBarrierList(enemy, self.wall_list, grid_size, playing_field_left_boundary, playing_field_right_boundary, playing_field_bottom_boundary, playing_field_top_boundary) def on_draw(self): """ Render the screen. """ # This command has to happen before we start drawing self.clear() # Draw all the sprites. self.player_list.draw() self.wall_list.draw() self.enemy_list.draw() if self.path: arcade.draw_line_strip(self.path, arcade.color.BLUE, 2) def on_update(self, delta_time): """ Movement and game logic """ # Calculate speed based on the keys pressed self.player.change_x = 0 self.player.change_y = 0 if self.up_pressed and not self.down_pressed: self.player.change_y = MOVEMENT_SPEED elif self.down_pressed and not self.up_pressed: self.player.change_y = -MOVEMENT_SPEED if self.left_pressed and not self.right_pressed: self.player.change_x = -MOVEMENT_SPEED elif self.right_pressed and not self.left_pressed: self.player.change_x = MOVEMENT_SPEED # Update the character self.physics_engine.update() # Calculate a path to the player enemy = self.enemy_list[0] # Set to True if we can move diagonally. Note that diagonal movement # might cause the enemy to clip corners. self.path = arcade.astar_calculate_path(enemy.position, self.player.position, self.barrier_list, diagonal_movement=False) # print(self.path,"->", self.player.position) # --- Manage Scrolling --- # Keep track of if we changed the boundary. We don't want to call the # set_viewport command if we didn't change the view port. changed = False # Scroll left left_boundary = self.view_left + VIEWPORT_MARGIN if self.player.left < left_boundary: self.view_left -= left_boundary - self.player.left changed = True # Scroll right right_boundary = self.view_left + SCREEN_WIDTH - VIEWPORT_MARGIN if self.player.right > right_boundary: self.view_left += self.player.right - right_boundary changed = True # Scroll up top_boundary = self.view_bottom + SCREEN_HEIGHT - VIEWPORT_MARGIN if self.player.top > top_boundary: self.view_bottom += self.player.top - top_boundary changed = True # Scroll down bottom_boundary = self.view_bottom + VIEWPORT_MARGIN if self.player.bottom < bottom_boundary: self.view_bottom -= bottom_boundary - self.player.bottom changed = True # Make sure our boundaries are integer values. While the view port does # support floating point numbers, for this application we want every pixel # in the view port to map directly onto a pixel on the screen. We don't want # any rounding errors. self.view_left = int(self.view_left) self.view_bottom = int(self.view_bottom) # If we changed the boundary values, update the view port to match if changed: arcade.set_viewport(self.view_left, SCREEN_WIDTH + self.view_left, self.view_bottom, SCREEN_HEIGHT + 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 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 function """ window = MyGame(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_TITLE) window.setup() arcade.run() if __name__ == "__main__": main() ```