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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_scale
s of the endpoints of the respective segments. If the default methods are used and the weight_scale
s of all points are set to 1.0
, then this equals the sum of Euclidean distances of all segments in the path.
Methods¶
_compute_cost ( int from_id, int to_id ) virtual const |
|
_estimate_cost ( int from_id, int to_id ) virtual const |
|
void |
add_point ( int id, Vector3 position, float weight_scale=1.0 ) |
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 ) |
get_available_point_id ( ) const |
|
get_closest_point ( Vector3 to_position, bool include_disabled=false ) const |
|
get_closest_position_in_segment ( Vector3 to_position ) const |
|
get_id_path ( int from_id, int to_id ) |
|
get_point_capacity ( ) const |
|
get_point_connections ( int id ) |
|
get_point_count ( ) const |
|
get_point_ids ( ) |
|
get_point_path ( int from_id, int to_id ) |
|
get_point_position ( int id ) const |
|
get_point_weight_scale ( int id ) const |
|
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_scale
s 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.