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#
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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()
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