Source: d:/wamp/www/phaser/src/pixi/display/Stage.js

/**
 * @author Mat Groves http://matgroves.com/ @Doormat23
 */

/**
 * A Stage represents the root of the display tree. Everything connected to the stage is rendered
 *
 * @class Stage
 * @extends DisplayObjectContainer
 * @constructor
 * @param backgroundColor {Number} the background color of the stage, you have to pass this in is in hex format
 *      like: 0xFFFFFF for white
 * 
 * Creating a stage is a mandatory process when you use Pixi, which is as simple as this : 
 * var stage = new PIXI.Stage(0xFFFFFF);
 * where the parameter given is the background colour of the stage, in hex
 * you will use this stage instance to add your sprites to it and therefore to the renderer
 * Here is how to add a sprite to the stage : 
 * stage.addChild(sprite);
 */
PIXI.Stage = function(backgroundColor)
{
    PIXI.DisplayObjectContainer.call( this );

    /**
     * [read-only] Current transform of the object based on world (parent) factors
     *
     * @property worldTransform
     * @type Matrix
     * @readOnly
     * @private
     */
    this.worldTransform = new PIXI.Matrix();

    /**
     * Whether or not the stage is interactive
     *
     * @property interactive
     * @type Boolean
     */
    this.interactive = true;

    /**
     * The interaction manage for this stage, manages all interactive activity on the stage
     *
     * @property interactionManager
     * @type InteractionManager
     */
    this.interactionManager = new PIXI.InteractionManager(this);

    /**
     * Whether the stage is dirty and needs to have interactions updated
     *
     * @property dirty
     * @type Boolean
     * @private
     */
    this.dirty = true;

    //the stage is its own stage
    this.stage = this;

    //optimize hit detection a bit
    this.stage.hitArea = new PIXI.Rectangle(0, 0, 100000, 100000);

    this.setBackgroundColor(backgroundColor);
};

// constructor
PIXI.Stage.prototype = Object.create( PIXI.DisplayObjectContainer.prototype );
PIXI.Stage.prototype.constructor = PIXI.Stage;

/**
 * Sets another DOM element which can receive mouse/touch interactions instead of the default Canvas element.
 * This is useful for when you have other DOM elements on top of the Canvas element.
 *
 * @method setInteractionDelegate
 * @param domElement {DOMElement} This new domElement which will receive mouse/touch events
 */
PIXI.Stage.prototype.setInteractionDelegate = function(domElement)
{
    this.interactionManager.setTargetDomElement( domElement );
};

/*
 * Updates the object transform for rendering
 *
 * @method updateTransform
 * @private
 */
PIXI.Stage.prototype.updateTransform = function()
{
    this.worldAlpha = 1;

    for(var i=0,j=this.children.length; i<j; i++)
    {
        this.children[i].updateTransform();
    }

    if(this.dirty)
    {
        this.dirty = false;
        // update interactive!
        this.interactionManager.dirty = true;
    }

    if(this.interactive)this.interactionManager.update();
};

/**
 * Sets the background color for the stage
 *
 * @method setBackgroundColor
 * @param backgroundColor {Number} the color of the background, easiest way to pass this in is in hex format
 *      like: 0xFFFFFF for white
 */
PIXI.Stage.prototype.setBackgroundColor = function(backgroundColor)
{
    this.backgroundColor = backgroundColor || 0x000000;
    this.backgroundColorSplit = PIXI.hex2rgb(this.backgroundColor);
    var hex = this.backgroundColor.toString(16);
    hex = '000000'.substr(0, 6 - hex.length) + hex;
    this.backgroundColorString = '#' + hex;
};

/**
 * This will return the point containing global coordinates of the mouse.
 *
 * @method getMousePosition
 * @return {Point} A point containing the coordinates of the global InteractionData position.
 */
PIXI.Stage.prototype.getMousePosition = function()
{
    return this.interactionManager.mouse.global;
};