![]() # This line ensures that the neighboring cell is part of our walkable cells. # To find the neighbors, we try to move one cell in every possible direction and is ensure that # this cell is walkable and not already connected. func _find_neighbor_indices(cell: Vector2, cell_mappings: Dictionary) -> Array: # Returns an array of the `cell`'s connectable neighbors. connect_points(cell_mappings, neighbor_index) # The nnect_points() function connects two points on the graph by index, *not* # by coordinates. for point in cell_mappings:įor neighbor_index in _find_neighbor_indices(point, cell_mappings): We use # another function to find the neighbors given a cell's coordinates. # Then, we loop over the points again, and we connect them with all their neighbors. # We pass each cell's unique index and the corresponding Vector2 coordinates to the # AStar2D.add_point() function. First, we register all our points in the AStar graph. func _add_and_connect_points(cell_mappings: Dictionary) -> void: # Adds and connects the walkable cells to the Astar2D object. # The AStar2D object then finds the best path between the two indices. If not, we return an empty # PoolVector2Array() to avoid errors. # We just ensure that the AStar graph has both points defined. # Our Grid.as_index() method does just that. This is why we # need a reliable way to calculate an index given some input coordinates. ![]() # With the AStar algorithm, we have to use the points' indices to get a path. func calculate_point_path(start: Vector2, end: Vector2) -> PoolVector2Array: # Returns the path found between `start` and `end` as an array of Vector2 coordinates. # We then add all the cells to our AStar2D instance and connect them to create our pathfinding # graph. # For each cell, we define a key-value pair of cell coordinates: index.Ĭell_mappings = _grid. Doing so here slightly # simplifies the code and improves performance a bit. Here, # we cache a mapping between cell coordinates and their unique index. # To create our AStar graph, we will need the index value corresponding to each grid cell. # Because we will instantiate the `PathFinder` from our UnitPath's script, we pass it the data it # needs to initialize itself via its constructor function, _init(). func _init(grid: Grid, walkable_cells: Array) -> void: # Initializes the Astar2D object upon creation. Our script is mostly # here to initialize that object. Var _grid: Resource # This variable holds an AStar2D instance that will do the actual pathfinding. It defines the directions in which we allow a unit # to move in the game: up, left, right, down. # Finds the path between two points among walkable cells using the AStar pathfinding algorithm.Įxtends Reference # We will use that constant in "for" loops later. Here is the code for the PathFinder class. With this method, we can calculate a unique index for each cell coordinates in our grid. This is where our grid class comes in handy with its as_index() method. You can already see the catch: the AStar object works with unique IDs for each point in the graph. The algorithm outputs a list of coordinates through which you need to navigate to reach the end. ![]() Once the graph is set, you call the find_path() function with the indices corresponding to two points: the start and the end. ![]() In the case of a grid, you should connect each cell to its unoccupied neighbors. Connect all the points that should form a walkable path, using the points' indices.Add a list of points to the object, giving each a unique index.You could use it for a road or train network in an open-world game, for example. While it’s often presented in games with grids, the AStar algorithm is flexible. If you want to learn to implement the AStar pathfinding algorithm itself, check out the Introduction to the A* Algorithm on Red Blob Games. Godot comes with the algorithm implemented and optimized for you. We will use it to move units to a cell picked by the player, but also to display a preview of the path the unit will walk, inspired by Fire Emblem. In this lesson, we will create a PathFinder class that extends Godot’s built-in AStar2D, an implementation of the AStar pathfinding algorithm.
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