mirror of
https://github.com/OpenDiablo2/OpenDiablo2
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dd21809288
Copied go-astar into d2common/d2astar, made a few optimizations. Runs roughly 30% faster according to my benchmarking. Added a `maxCost` param to prevent searching the entire map for a path. This probably needs tweaked a bit, but follows the original game more closely. Co-authored-by: Nicholas Eden <neden@zigzagame.com>
154 lines
3.8 KiB
Markdown
154 lines
3.8 KiB
Markdown
D2 A*
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========
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**A\* pathfinding implementation for OpenDiablo2**
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***Forked from [go-astar](https://github.com/beefsack/go-astar)***
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Changes
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-------
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* Used [sync.Pool](https://golang.org/pkg/sync/#Pool) to reuse objects created during pathfinding. This improves performance by roughly 30% by reducing allocations.
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* Added a check on the target for neighbors to identify if the user clicked an inaccessible area.
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* Added a max cost to prevent searching the entire region for a path.
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TODO
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------
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* Evaluate bi-directional A*, specifically if it would more quickly identify if the user clicked an in inaccessible area (such as an island).
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The [A\* pathfinding algorithm](http://en.wikipedia.org/wiki/A*_search_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.
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A fantastic overview of A\* can be found at [Amit Patel's Stanford website](http://theory.stanford.edu/~amitp/GameProgramming/AStarComparison.html).
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Examples
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--------
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The following crude examples were taken directly from the automated tests. Please see `path_test.go` for more examples.
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### Key
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* `.` - Plain (movement cost 1)
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* `~` - River (movement cost 2)
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* `M` - Mountain (movement cost 3)
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* `X` - Blocker, unable to move through
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* `F` - From / start position
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* `T` - To / goal position
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* `●` - Calculated path
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### Straight line
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```
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.....~...... .....~......
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.....MM..... .....MM.....
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.F........T. -> .●●●●●●●●●●.
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....MMM..... ....MMM.....
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............ ............
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```
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### Around a mountain
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```
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.....~...... .....~......
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.....MM..... .....MM.....
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.F..MMMM..T. -> .●●●MMMM●●●.
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....MMM..... ...●MMM●●...
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............ ...●●●●●....
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```
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### Blocked path
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```
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............
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.........XXX
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.F.......XTX -> No path
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.........XXX
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............
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```
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### Maze
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```
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FX.X........ ●X.X●●●●●●..
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.X...XXXX.X. ●X●●●XXXX●X.
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.X.X.X....X. -> ●X●X.X●●●●X.
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...X.X.XXXXX ●●●X.X●XXXXX
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.XX..X.....T .XX..X●●●●●●
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```
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### Mountain climber
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```
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..F..M...... ..●●●●●●●●●.
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.....MM..... .....MM...●.
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....MMMM..T. -> ....MMMM..●.
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....MMM..... ....MMM.....
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............ ............
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```
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### River swimmer
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```
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.....~...... .....~......
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.....~...... ....●●●.....
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.F...X...T.. -> .●●●●X●●●●..
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.....M...... .....M......
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.....M...... .....M......
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```
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Usage
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-----
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### Import the package
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```go
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import "github.com/beefsack/go-astar"
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```
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### Implement Pather interface
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An example implementation is done for the tests in `path_test.go` for the Tile type.
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The `PathNeighbors` method should return a slice of the direct neighbors.
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The `PathNeighborCost` method should calculate an exact movement cost for direct neighbors.
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The `PathEstimatedCost` is a heuristic method for estimating the distance between arbitrary tiles. The examples in the test files use [Manhattan distance](http://en.wikipedia.org/wiki/Taxicab_geometry) to estimate orthogonal distance between tiles.
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```go
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type Tile struct{}
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func (t *Tile) PathNeighbors() []astar.Pather {
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return []astar.Pather{
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t.Up(),
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t.Right(),
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t.Down(),
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t.Left(),
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}
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}
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func (t *Tile) PathNeighborCost(to astar.Pather) float64 {
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return to.MovementCost
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}
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func (t *Tile) PathEstimatedCost(to astar.Pather) float64 {
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return t.ManhattanDistance(to)
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}
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```
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### Call Path function
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```go
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// t1 and t2 are *Tile objects from inside the world.
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path, distance, found := astar.Path(t1, t2)
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if !found {
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log.Println("Could not find path")
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}
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// path is a slice of Pather objects which you can cast back to *Tile.
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```
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Authors
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-------
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Michael Alexander <beefsack@gmail.com>
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Robin Ranjit Chauhan <robin@pathwayi.com>
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