OpenDiablo2/d2common/d2astar

D2 A*

A* pathfinding implementation for OpenDiablo2

Forked from go-astar

Changes

• Used sync.Pool to reuse objects created during path-finding. This improves performance by roughly 30% by reducing allocations.
• Added a max cost to prevent searching the entire region for a path.
• If there is no path the target within the max cost, the path found that gets closest to target will be returned. This allows the player to click in inaccessible areas causing the character to run along the edge.

TODO

• Evaluate bi-directional A*, specifically if it would more quickly identify if the user clicked an in inaccessible area (such as an island).

The A* pathfinding algorithm is a pathfinding algorithm noted for its performance and accuracy and is commonly used in game development. It can be used to find short paths for any weighted graph.

A fantastic overview of A* can be found at Amit Patel's Stanford website.

Examples

The following crude examples were taken directly from the automated tests. Please see path_test.go for more examples.

Key

• . - Plain (movement cost 1)
• ~ - River (movement cost 2)
• M - Mountain (movement cost 3)
• X - Blocker, unable to move through
• F - From / start position
• T - To / goal position
• ● - Calculated path

Straight line

.....~......      .....~......
.....MM.....      .....MM.....
.F........T.  ->  .●●●●●●●●●●.
....MMM.....      ....MMM.....
............      ............

Around a mountain

.....~......      .....~......
.....MM.....      .....MM.....
.F..MMMM..T.  ->  .●●●MMMM●●●.
....MMM.....      ...●MMM●●...
............      ...●●●●●....

Blocked path

............      
.........XXX
.F.......XTX  ->  No path
.........XXX
............

Maze

FX.X........      ●X.X●●●●●●..
.X...XXXX.X.      ●X●●●XXXX●X.
.X.X.X....X.  ->  ●X●X.X●●●●X.
...X.X.XXXXX      ●●●X.X●XXXXX
.XX..X.....T      .XX..X●●●●●●

Mountain climber

..F..M......      ..●●●●●●●●●.
.....MM.....      .....MM...●.
....MMMM..T.  ->  ....MMMM..●.
....MMM.....      ....MMM.....
............      ............

River swimmer

.....~......      .....~......
.....~......      ....●●●.....
.F...X...T..  ->  .●●●●X●●●●..
.....M......      .....M......
.....M......      .....M......

Usage

Import the package

import "github.com/beefsack/go-astar"

Implement Pather interface

An example implementation is done for the tests in path_test.go for the Tile type.

The PathNeighbors method should return a slice of the direct neighbors.

The PathNeighborCost method should calculate an exact movement cost for direct neighbors.

The PathEstimatedCost is a heuristic method for estimating the distance between arbitrary tiles. The examples in the test files use Manhattan distance to estimate orthogonal distance between tiles.

type Tile struct{}

func (t *Tile) PathNeighbors() []astar.Pather {
	return []astar.Pather{
		t.Up(),
		t.Right(),
		t.Down(),
		t.Left(),
	}
}

func (t *Tile) PathNeighborCost(to astar.Pather) float64 {
	return to.MovementCost
}

func (t *Tile) PathEstimatedCost(to astar.Pather) float64 {
	return t.ManhattanDistance(to)
}

Call Path function

// t1 and t2 are *Tile objects from inside the world.
path, distance, found := astar.Path(t1, t2)
if !found {
	log.Println("Could not find path")
}
// path is a slice of Pather objects which you can cast back to *Tile.

Authors

Michael Alexander beefsack@gmail.com Robin Ranjit Chauhan robin@pathwayi.com