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 godot.AStar.addPoint
and create segments manually with godot.AStar.connectPoints
. Then you can test if there is a path between two points with the godot.AStar.arePointsConnected
function, get a path containing indices by godot.AStar.getIdPath
, or one containing actual coordinates with godot.AStar.getPointPath
.
It is also possible to use non-Euclidean distances. To do so, create a class that extends AStar
and override methods godot.AStar._ComputeCost
and godot.AStar._EstimateCost
. Both take two indices and return a length, as is shown in the following example.
class MyAStar:
extends AStar
func _compute_cost(u, v):
return abs(u - v)
func _estimate_cost(u, v):
return min(0, abs(u - v) - 1)
godot.AStar._EstimateCost
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 godot.AStar._EstimateCost
return the same value as godot.AStar._ComputeCost
to provide the algorithm with the most accurate information.
If the default godot.AStar._EstimateCost
and godot.AStar._ComputeCost
methods are used, or if the supplied godot.AStar._EstimateCost
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 godot.AStar._ComputeCost
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.
Constructor
Methods
_ComputeCost(fromId:Int, toId:Int):Single
Called when computing the cost between two connected points.
Note that this function is hidden in the default AStar
class.
_EstimateCost(fromId:Int, toId:Int):Single
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.
addPoint(id:Int, position:Vector3, ?weightScale:Single):Void
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 godot.AStar._ComputeCost
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 = AStar.new()
astar.add_point(1, 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.
arePointsConnected(id:Int, toId:Int, ?bidirectional:Bool):Bool
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.
connectPoints(id:Int, toId:Int, ?bidirectional:Bool):Void
Creates a segment between the given points. If bidirectional
is false
, only movement from id
to to_id
is allowed, not the reverse direction.
var astar = AStar.new()
astar.add_point(1, Vector3(1, 1, 0))
astar.add_point(2, Vector3(0, 5, 0))
astar.connect_points(1, 2, false)
disconnectPoints(id:Int, toId:Int, ?bidirectional:Bool):Void
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.
getClosestPoint(toPosition:Vector3, ?includeDisabled:Bool):Int
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.
getClosestPositionInSegment(toPosition:Vector3):Vector3
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.
inlinegetIdPath(fromId:Int, toId:Int):Array<Int>
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.
var astar = AStar.new()
astar.add_point(1, Vector3(0, 0, 0))
astar.add_point(2, Vector3(0, 1, 0), 1) # Default weight is 1
astar.add_point(3, Vector3(1, 1, 0))
astar.add_point(4, Vector3(2, 0, 0))
astar.connect_points(1, 2, false)
astar.connect_points(2, 3, false)
astar.connect_points(4, 3, false)
astar.connect_points(1, 4, false)
var res = astar.get_id_path(1, 3) # Returns [1, 2, 3]
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.
getPointCapacity():Int
Returns the capacity of the structure backing the points, useful in conjunction with reserve_space
.
inlinegetPointConnections(id:Int):Array<Int>
Returns an array with the IDs of the points that form the connection with the given point.
var astar = AStar.new()
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, 2, true)
astar.connect_points(1, 3, true)
var neighbors = astar.get_point_connections(1) # Returns [2, 3]
inlinegetPointPath(fromId:Int, toId:Int):Array<Vector3>
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.
Note: This method is not thread-safe. If called from a godot.Thread
, it will return an empty godot.Vector3
and will print an error message.
getPointWeightScale(id:Int):Single
Returns the weight scale of the point associated with the given id
.
isPointDisabled(id:Int):Bool
Returns whether a point is disabled or not for pathfinding. By default, all points are enabled.
reserveSpace(numNodes:Int):Void
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.
setPointDisabled(id:Int, ?disabled:Bool):Void
Disables or enables the specified point for pathfinding. Useful for making a temporary obstacle.
setPointWeightScale(id:Int, weightScale:Single):Void
Sets the weight_scale
for the point with the given id
. The weight_scale
is multiplied by the result of godot.AStar._ComputeCost
when determining the overall cost of traveling across a segment from a neighboring point to this point.