Jump To …

graph.js

javascript-astar http://github.com/bgrins/javascript-astar Freely distributable under the MIT License. Includes Binary Heap (with modifications) from Marijn Haverbeke. http://eloquentjavascript.net/appendix2.html

 
var GraphNodeType = { 
    OPEN: 0, 
    WALL: 1 
};

Creates a Graph class used in the astar search algorithm.

 
function Graph(grid) {
    var nodes = [];

    for (var x = 0; x < grid.length; x++) {
        nodes[x] = [];
        
        for (var y = 0, row = grid[x]; y < row.length; y++) {
            nodes[x][y] = new GraphNode(x, y, row[y]);
        }
    }

    this.input = grid;
    this.nodes = nodes;
}

Graph.prototype.toString = function() {
    var graphString = "\n";
    var nodes = this.nodes;
    var rowDebug, row, y, l;
    for (var x = 0, len = nodes.length; x < len; x++) {
        rowDebug = "";
        row = nodes[x];
        for (y = 0, l = row.length; y < l; y++) {
            rowDebug += row[y].type + " ";
        }
        graphString = graphString + rowDebug + "\n";
    }
    return graphString;
};

function GraphNode(x,y,type) {
    this.data = { };
    this.x = x;
    this.y = y;
    this.pos = {
        x: x, 
        y: y
    };
    this.type = type;
}

GraphNode.prototype.toString = function() {
    return "[" + this.x + " " + this.y + "]";
};

GraphNode.prototype.isWall = function() {
    return this.type == GraphNodeType.WALL;
};


function BinaryHeap(scoreFunction){
    this.content = [];
    this.scoreFunction = scoreFunction;
}

BinaryHeap.prototype = {
    push: function(element) {

Add the new element to the end of the array.

 
        this.content.push(element);

Allow it to sink down.

 
        this.sinkDown(this.content.length - 1);
    },
    pop: function() {

Store the first element so we can return it later.

 
        var result = this.content[0];

Get the element at the end of the array.

 
        var end = this.content.pop();

If there are any elements left, put the end element at the start, and let it bubble up.

 
        if (this.content.length > 0) {
             this.content[0] = end;
             this.bubbleUp(0);
        }
        return result;
    },
    remove: function(node) {
        var i = this.content.indexOf(node);

When it is found, the process seen in 'pop' is repeated to fill up the hole.

 
        var end = this.content.pop();

        if (i !== this.content.length - 1) {
            this.content[i] = end;
            
            if (this.scoreFunction(end) < this.scoreFunction(node)) {
                this.sinkDown(i);
            }
            else {
                this.bubbleUp(i);
            }
        }
    },
    size: function() {
        return this.content.length;
    },
    rescoreElement: function(node) {
        this.sinkDown(this.content.indexOf(node));
    },
    sinkDown: function(n) {

Fetch the element that has to be sunk.

 
        var element = this.content[n];

When at 0, an element can not sink any further.

 
        while (n > 0) {

Compute the parent element's index, and fetch it.

 
            var parentN = ((n + 1) >> 1) - 1,
                parent = this.content[parentN];

Swap the elements if the parent is greater.

 
            if (this.scoreFunction(element) < this.scoreFunction(parent)) {
                this.content[parentN] = element;
                this.content[n] = parent;

Update 'n' to continue at the new position.

 
                n = parentN;
            }

Found a parent that is less, no need to sink any further.

 
            else {
                break;
            }
        }
    },
    bubbleUp: function(n) {

Look up the target element and its score.

 
        var length = this.content.length,
            element = this.content[n],
            elemScore = this.scoreFunction(element);
        
        while(true) {

Compute the indices of the child elements.

 
            var child2N = (n + 1) << 1, child1N = child2N - 1;

This is used to store the new position of the element, if any.

 
            var swap = null;

If the first child exists (is inside the array)...

 
            if (child1N < length) {

Look it up and compute its score.

 
            var child1 = this.content[child1N],
                child1Score = this.scoreFunction(child1);

If the score is less than our element's, we need to swap.

 
            if (child1Score < elemScore)
                swap = child1N;
            }

Do the same checks for the other child.

 
            if (child2N < length) {
                var child2 = this.content[child2N],
                    child2Score = this.scoreFunction(child2);
                if (child2Score < (swap === null ? elemScore : child1Score)) {
                    swap = child2N;
                }
            }

If the element needs to be moved, swap it, and continue.

 
            if (swap !== null) {
                this.content[n] = this.content[swap];
                this.content[swap] = element;
                n = swap;
            }

Otherwise, we are done.

 
            else {
                break;
            }
        }
    }
};