AStar

An implementation of A* to find shortest paths among connected points in space.

A* (A star) is a computer algorithm that is widely used in pathfinding and graph traversal, the process of plotting short paths among vertices (points), passing through a given set of edges (segments). It enjoys widespread use due to its performance and accuracy. Godot’s A* implementation uses points in three-dimensional space and Euclidean distances by default.

You must add points manually with and create segments manually with connect_points. Then you can test if there is a path between two points with the function, get a path containing indices by get_id_path, or one containing actual coordinates with .

It is also possible to use non-Euclidean distances. To do so, create a class that extends and override methods _compute_cost and . Both take two indices and return a length, as is shown in the following example.

_estimate_cost should return a lower bound of the distance, i.e. _estimate_cost(u, v) <= _compute_cost(u, v). This serves as a hint to the algorithm because the custom _compute_cost might be computation-heavy. If this is not the case, make return the same value as _compute_cost to provide the algorithm with the most accurate information.

If the default and _compute_cost methods are used, or if the supplied method returns a lower bound of the cost, then the paths returned by A* will be the lowest cost paths. Here, the cost of a path equals to the sum of the _compute_cost results of all segments in the path multiplied by the weight_scales of the end points of the respective segments. If the default methods are used and the weight_scales of all points are set to 1.0, then this equals to the sum of Euclidean distances of all segments in the path.

• _compute_cost ( int from_id, to_id ) virtual

Called when computing the cost between two connected points.

Note that this function is hidden in the default AStar class.

• float _estimate_cost ( from_id, int to_id ) virtual

Called when estimating the cost between a point and the path’s ending point.

Note that this function is hidden in the default AStar class.

• void add_point ( id, Vector3 position, weight_scale=1.0 )

Adds a new point at the given position with the given identifier. The id must be 0 or larger, and the weight_scale must be 1 or larger.

The weight_scale is multiplied by the result of _compute_cost when determining the overall cost of traveling across a segment from a neighboring point to this point. Thus, all else being equal, the algorithm prefers points with lower weight_scales to form a path.

var astar = AStar.new()
astar.add_point(1, Vector3(1, 0, 0), 4) # Adds the point (1, 0, 0) with weight_scale 4 and id 1

• are_points_connected ( int id, to_id, bool bidirectional=true ) const

Returns whether the two given points are directly connected by a segment. If bidirectional is false, returns whether movement from id to to_id is possible through this segment.

• void clear ( )

Clears all the points and segments.

• void connect_points ( id, int to_id, bidirectional=true )

Creates a segment between the given points. If bidirectional is , only movement from id to to_id is allowed, not the reverse direction.

• void disconnect_points ( int id, to_id, bool bidirectional=true )

Deletes the segment between the given points. If bidirectional is false, only movement from id to to_id is prevented, and a unidirectional segment possibly remains.

• get_available_point_id ( ) const

Returns the next available point ID with no point associated to it.

• int get_closest_point ( to_position, bool include_disabled=false ) const

Returns the ID of the closest point to to_position, optionally taking disabled points into account. Returns -1 if there are no points in the points pool.

Note: If several points are the closest to to_position, the one with the smallest ID will be returned, ensuring a deterministic result.

Returns the closest position to to_position that resides inside a segment between two connected points.

var astar = AStar.new()
astar.add_point(1, Vector3(0, 0, 0))
astar.add_point(2, Vector3(0, 5, 0))
astar.connect_points(1, 2)
var res = astar.get_closest_position_in_segment(Vector3(3, 3, 0)) # Returns (0, 3, 0)

The result is in the segment that goes from y = 0 to y = 5. It’s the closest position in the segment to the given point.

• get_id_path ( int from_id, to_id )

Returns an array with the IDs of the points that form the path found by AStar between the given points. The array is ordered from the starting point to the ending point of the path.

If you change the 2nd point’s weight to 3, then the result will be [1, 4, 3] instead, because now even though the distance is longer, it’s “easier” to get through point 4 than through point 2.

• int get_point_capacity ( ) const

Returns the capacity of the structure backing the points, useful in conjunction with reserve_space.

• get_point_connections ( int id )

astar.add_point(1, Vector3(0, 0, 0))
astar.add_point(2, Vector3(0, 1, 0))
astar.add_point(3, Vector3(1, 1, 0))
astar.add_point(4, Vector3(2, 0, 0))
astar.connect_points(1, 3, true)
var neighbors = astar.get_point_connections(1) # Returns [2, 3]

• get_point_count ( ) const

Returns the number of points currently in the points pool.

• PoolVector3Array get_point_path ( from_id, int to_id )

Returns an array with the points that are in the path found by AStar between the given points. The array is ordered from the starting point to the ending point of the path.

• get_point_position ( int id ) const

Returns the position of the point associated with the given id.

• get_point_weight_scale ( int id ) const

Returns the weight scale of the point associated with the given id.

• get_points ( )

Returns an array of all points.

• bool has_point ( id ) const

Returns whether a point associated with the given id exists.

• bool is_point_disabled ( id ) const

Returns whether a point is disabled or not for pathfinding. By default, all points are enabled.

• void remove_point ( int id )

Removes the point associated with the given id from the points pool.

• void reserve_space ( num_nodes )

Reserves space internally for num_nodes points, useful if you’re adding a known large number of points at once, for a grid for instance. New capacity must be greater or equals to old capacity.

• void set_point_disabled ( int id, disabled=true )

Disables or enables the specified point for pathfinding. Useful for making a temporary obstacle.

• void set_point_position ( int id, position )

Sets the position for the point with the given id.

Sets the weight_scale for the point with the given id. The weight_scale is multiplied by the result of _compute_cost when determining the overall cost of traveling across a segment from a neighboring point to this point.