Source: src/math/QuadTree.js

/**
 * @author       Timo Hausmann
 * @author       Richard Davey <rich@photonstorm.com>
 * @copyright    2016 Photon Storm Ltd.
 * @license      {@link https://github.com/photonstorm/phaser/blob/master/license.txt|MIT License}
 */

/**
* A QuadTree implementation. The original code was a conversion of the Java code posted to GameDevTuts.
* However I've tweaked it massively to add node indexing, removed lots of temp. var creation and significantly increased performance as a result.
* Original version at https://github.com/timohausmann/quadtree-js/
*
* @class Phaser.QuadTree
* @constructor
* @param {number} x - The top left coordinate of the quadtree.
* @param {number} y - The top left coordinate of the quadtree.
* @param {number} width - The width of the quadtree in pixels.
* @param {number} height - The height of the quadtree in pixels.
* @param {number} [maxObjects=10] - The maximum number of objects per node.
* @param {number} [maxLevels=4] - The maximum number of levels to iterate to.
* @param {number} [level=0] - Which level is this?
*/
Phaser.QuadTree = function(x, y, width, height, maxObjects, maxLevels, level) {

    /**
    * @property {number} maxObjects - The maximum number of objects per node.
    * @default
    */
    this.maxObjects = 10;

    /**
    * @property {number} maxLevels - The maximum number of levels to break down to.
    * @default
    */
    this.maxLevels = 4;

    /**
    * @property {number} level - The current level.
    */
    this.level = 0;

    /**
    * @property {object} bounds - Object that contains the quadtree bounds.
    */
    this.bounds = {};

    /**
    * @property {array} objects - Array of quadtree children.
    */
    this.objects = [];

    /**
    * @property {array} nodes - Array of associated child nodes.
    */
    this.nodes = [];

    /**
    * @property {array} _empty - Internal empty array.
    * @private
    */
    this._empty = [];

    this.reset(x, y, width, height, maxObjects, maxLevels, level);

};

Phaser.QuadTree.prototype = {

    /**
    * Resets the QuadTree.
    *
    * @method Phaser.QuadTree#reset
    * @param {number} x - The top left coordinate of the quadtree.
    * @param {number} y - The top left coordinate of the quadtree.
    * @param {number} width - The width of the quadtree in pixels.
    * @param {number} height - The height of the quadtree in pixels.
    * @param {number} [maxObjects=10] - The maximum number of objects per node.
    * @param {number} [maxLevels=4] - The maximum number of levels to iterate to.
    * @param {number} [level=0] - Which level is this?
    */
    reset: function (x, y, width, height, maxObjects, maxLevels, level) {

        this.maxObjects = maxObjects || 10;
        this.maxLevels = maxLevels || 4;
        this.level = level || 0;

        this.bounds = {
            x: Math.round(x),
            y: Math.round(y),
            width: width,
            height: height,
            subWidth: Math.floor(width / 2),
            subHeight: Math.floor(height / 2),
            right: Math.round(x) + Math.floor(width / 2),
            bottom: Math.round(y) + Math.floor(height / 2)
        };

        this.objects.length = 0;
        this.nodes.length = 0;

    },

    /**
    * Populates this quadtree with the children of the given Group. In order to be added the child must exist and have a body property.
    *
    * @method Phaser.QuadTree#populate
    * @param {Phaser.Group} group - The Group to add to the quadtree.
    */
    populate: function (group) {

        group.forEach(this.populateHandler, this, true);

    },

    /**
    * Handler for the populate method.
    *
    * @method Phaser.QuadTree#populateHandler
    * @param {Phaser.Sprite|object} sprite - The Sprite to check.
    */
    populateHandler: function (sprite) {

        if (sprite.body && sprite.exists)
        {
            this.insert(sprite.body);
        }

    },

    /**
    * Split the node into 4 subnodes
    *
    * @method Phaser.QuadTree#split
    */
    split: function () {

        //  top right node
        this.nodes[0] = new Phaser.QuadTree(this.bounds.right, this.bounds.y, this.bounds.subWidth, this.bounds.subHeight, this.maxObjects, this.maxLevels, (this.level + 1));

        //  top left node
        this.nodes[1] = new Phaser.QuadTree(this.bounds.x, this.bounds.y, this.bounds.subWidth, this.bounds.subHeight, this.maxObjects, this.maxLevels, (this.level + 1));

        //  bottom left node
        this.nodes[2] = new Phaser.QuadTree(this.bounds.x, this.bounds.bottom, this.bounds.subWidth, this.bounds.subHeight, this.maxObjects, this.maxLevels, (this.level + 1));

        //  bottom right node
        this.nodes[3] = new Phaser.QuadTree(this.bounds.right, this.bounds.bottom, this.bounds.subWidth, this.bounds.subHeight, this.maxObjects, this.maxLevels, (this.level + 1));

    },

    /**
    * Insert the object into the node. If the node exceeds the capacity, it will split and add all objects to their corresponding subnodes.
    *
    * @method Phaser.QuadTree#insert
    * @param {Phaser.Physics.Arcade.Body|object} body - The Body object to insert into the quadtree. Can be any object so long as it exposes x, y, right and bottom properties.
    */
    insert: function (body) {

        var i = 0;
        var index;

        //  if we have subnodes ...
        if (this.nodes[0] != null)
        {
            index = this.getIndex(body);

            if (index !== -1)
            {
                this.nodes[index].insert(body);
                return;
            }
        }

        this.objects.push(body);

        if (this.objects.length > this.maxObjects && this.level < this.maxLevels)        {
            //  Split if we don't already have subnodes
            if (this.nodes[0] == null)
            {
                this.split();
            }

            //  Add objects to subnodes
            while (i < this.objects.length)            {
                index = this.getIndex(this.objects[i]);

                if (index !== -1)
                {
                    //  this is expensive - see what we can do about it
                    this.nodes[index].insert(this.objects.splice(i, 1)[0]);
                }
                else
                {
                    i++;
                }
            }
        }

    },

    /**
    * Determine which node the object belongs to.
    *
    * @method Phaser.QuadTree#getIndex
    * @param {Phaser.Rectangle|object} rect - The bounds in which to check.
    * @return {number} index - Index of the subnode (0-3), or -1 if rect cannot completely fit within a subnode and is part of the parent node.
    */
    getIndex: function (rect) {

        //  default is that rect doesn't fit, i.e. it straddles the internal quadrants
        var index = -1;

        if (rect.x < this.bounds.right && rect.right < this.bounds.right)        {
            if (rect.y < this.bounds.bottom && rect.bottom < this.bounds.bottom)            {
                //  rect fits within the top-left quadrant of this quadtree
                index = 1;
            }
            else if (rect.y > this.bounds.bottom)
            {
                //  rect fits within the bottom-left quadrant of this quadtree
                index = 2;
            }
        }
        else if (rect.x > this.bounds.right)
        {
            //  rect can completely fit within the right quadrants
            if (rect.y < this.bounds.bottom && rect.bottom < this.bounds.bottom)            {
                //  rect fits within the top-right quadrant of this quadtree
                index = 0;
            }
            else if (rect.y > this.bounds.bottom)
            {
                //  rect fits within the bottom-right quadrant of this quadtree
                index = 3;
            }
        }

        return index;

    },

    /**
    * Return all objects that could collide with the given Sprite or Rectangle.
    *
    * @method Phaser.QuadTree#retrieve
    * @param {Phaser.Sprite|Phaser.Rectangle} source - The source object to check the QuadTree against. Either a Sprite or Rectangle.
    * @return {array} - Array with all detected objects.
    */
    retrieve: function (source) {

        if (source instanceof Phaser.Rectangle)
        {
            var returnObjects = this.objects;

            var index = this.getIndex(source);
        }
        else
        {
            if (!source.body)
            {
                return this._empty;
            }

            var returnObjects = this.objects;

            var index = this.getIndex(source.body);
        }

        if (this.nodes[0])
        {
            //  If rect fits into a subnode ..
            if (index !== -1)
            {
                returnObjects = returnObjects.concat(this.nodes[index].retrieve(source));
            }
            else
            {
                //  If rect does not fit into a subnode, check it against all subnodes (unrolled for speed)
                returnObjects = returnObjects.concat(this.nodes[0].retrieve(source));
                returnObjects = returnObjects.concat(this.nodes[1].retrieve(source));
                returnObjects = returnObjects.concat(this.nodes[2].retrieve(source));
                returnObjects = returnObjects.concat(this.nodes[3].retrieve(source));
            }
        }

        return returnObjects;

    },

    /**
    * Clear the quadtree.
    * @method Phaser.QuadTree#clear
    */
    clear: function () {

        this.objects.length = 0;

        var i = this.nodes.length;

        while (i--)
        {
            this.nodes[i].clear();
            this.nodes.splice(i, 1);
        }

        this.nodes.length = 0;
    }

};

Phaser.QuadTree.prototype.constructor = Phaser.QuadTree;

/**
* Javascript QuadTree
* @version 1.0
*
* @version 1.3, March 11th 2014
* @author Richard Davey
* The original code was a conversion of the Java code posted to GameDevTuts. However I've tweaked
* it massively to add node indexing, removed lots of temp. var creation and significantly
* increased performance as a result.
*
* Original version at https://github.com/timohausmann/quadtree-js/
*/

/**
* @copyright © 2012 Timo Hausmann
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/