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AStar3D¶

Inherits: RefCounted < Object

An implementation of A* for finding the shortest path between two vertices on a connected graph in 3D space.

描述¶

A* (A star) is a computer algorithm 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 3D space and Euclidean distances by default.

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

It is also possible to use non-Euclidean distances. To do so, create a class that extends AStar3D and override methods _compute_cost and _estimate_cost. Both take two indices and return a length, as is shown in the following example.

class MyAStar:
    extends AStar3D

    func _compute_cost(u, v):
        return abs(u - v)

    func _estimate_cost(u, v):
        return min(0, abs(u - v) - 1)

public partial class MyAStar : AStar3D
{
    public override float _ComputeCost(long fromId, long toId)
    {
        return Mathf.Abs((int)(fromId - toId));
    }

    public override float _EstimateCost(long fromId, long toId)
    {
        return Mathf.Min(0, Mathf.Abs((int)(fromId - toId)) - 1);
    }
}

_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 _estimate_cost return the same value as _compute_cost to provide the algorithm with the most accurate information.

If the default _estimate_cost and _compute_cost methods are used, or if the supplied _estimate_cost 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 the sum of the _compute_cost results of all segments in the path multiplied by the weight_scales of the endpoints 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 the sum of Euclidean distances of all segments in the path.

Methods¶

float	_compute_cost ( int from_id, int to_id ) virtual const
float	_estimate_cost ( int from_id, int to_id ) virtual const
void	add_point ( int id, Vector3 position, float weight_scale=1.0 )
bool	are_points_connected ( int id, int to_id, bool bidirectional=true ) const
void	clear ( )
void	connect_points ( int id, int to_id, bool bidirectional=true )
void	disconnect_points ( int id, int to_id, bool bidirectional=true )
int	get_available_point_id ( ) const
int	get_closest_point ( Vector3 to_position, bool include_disabled=false ) const
Vector3	get_closest_position_in_segment ( Vector3 to_position ) const
PackedInt64Array	get_id_path ( int from_id, int to_id )
int	get_point_capacity ( ) const
PackedInt64Array	get_point_connections ( int id )
int	get_point_count ( ) const
PackedInt64Array	get_point_ids ( )
PackedVector3Array	get_point_path ( int from_id, int to_id )
Vector3	get_point_position ( int id ) const
float	get_point_weight_scale ( int id ) const
bool	has_point ( int id ) const
bool	is_point_disabled ( int id ) const
void	remove_point ( int id )
void	reserve_space ( int num_nodes )
void	set_point_disabled ( int id, bool disabled=true )
void	set_point_position ( int id, Vector3 position )
void	set_point_weight_scale ( int id, float weight_scale )

Method Descriptions¶

float _compute_cost ( int from_id, int to_id ) virtual const

Called when computing the cost between two connected points.

Note that this function is hidden in the default AStar3D class.

float _estimate_cost ( int from_id, int to_id ) virtual const

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

Note that this function is hidden in the default AStar3D class.

void add_point ( int id, Vector3 position, float 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 0.0 or greater.

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 = AStar3D.new()
astar.add_point(1, Vector3(1, 0, 0), 4) # Adds the point (1, 0, 0) with weight_scale 4 and id 1

var astar = new AStar3D();
astar.AddPoint(1, new Vector3(1, 0, 0), 4); // Adds the point (1, 0, 0) with weight_scale 4 and id 1

If there already exists a point for the given id, its position and weight scale are updated to the given values.

bool are_points_connected ( int id, int 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 ( int id, int to_id,