108 lines
3.1 KiB
Markdown
108 lines
3.1 KiB
Markdown
## A-Star
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[](https://scrutinizer-ci.com/g/BlackScorp/astar/?branch=master)
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[](https://scrutinizer-ci.com/g/BlackScorp/astar/?branch=master)
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[](https://scrutinizer-ci.com/g/BlackScorp/astar/build-status/master)
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[A-star](https://en.wikipedia.org/wiki/A*_search_algorithm) is a path finding algorithm, written in PHP.
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It can find the shortest path between two points in a two dimensional array by using different heuristics.
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## Installation
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~~~
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composer require blackscorp/astar
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~~~
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## Usage
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first create a two dimensional array for your map
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~~~php
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$map = [
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[0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0],
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[0, 0, 0, 1, 1],
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[0, 0, 0, 1, 0],
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];
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~~~
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each key represent the x and y position of the map.
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each value of the array represents the costs, A-star tries to find a way with lowest costs.
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you can use negative keys if your map requires it.
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next convert the array to a Grid, a Grid is a collection of Nodes.
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~~~php
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$grid = new BlackScorp\Astar\Grid($map);
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~~~
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now you can fetch nodes from the Grid like so
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~~~php
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$startPosition = $grid->getPoint(3,1);
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$endPosition = $grid->getPoint(0,0);
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~~~
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at the end pass the grid to the astar and search for the shortests path
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~~~php
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$astar = new BlackScorp\Astar\Astar($grid);
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$nodes = $astar->search($startPosition,$endPosition);
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if(count($nodes) === 0){
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echo "Path not found";
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}else{
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foreach($nodes as $node){
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echo $node->getY().'/'.$node->getX().'<br/>';
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}
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}
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~~~
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## Settings
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by default diagonal directions are disabled, they can be enabled like so
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~~~php
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$astar->enableDiagonal();
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~~~
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as soon as the diagonal option is enabled, the algorithm use the [Manhattan](http://theory.stanford.edu/~amitp/GameProgramming/Heuristics.html) heuristic to find the shortest path.
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Manhattan is not precise but the caluclation costs are low, however you can use another heuristics like Diagonal or Euclidean with following code.
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~~~php
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$astar->setHeuristic(new BlackScorp\Astar\Heuristic\Euclidean());
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~~~
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you can also create a custom heuristic.
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## Block locations
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there are cases where you want to block a specific path completly, independant of the costs, you can do so with following code
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~~~php
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astar->blocked([3,2]);
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~~~
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this basicly means that in the initial map
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~~~php
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$map = [
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[0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0],
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[0, 2, 2, 0, 0],
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[0, 3, 0, 1, 1],
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[0, 0, 0, 1, 0],
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];
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~~~
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the values 3 and 2 cannot be passed.
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## Contribute
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Please feel free to make pull requests, there is still place for improvement, the Grid contains a two dimensional array which might be replaced by an SplFixedArray or something similar.
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Run the tests to be sure nothing break.
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## License
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A-Star is free software distributed under the terms of the MIT license.
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