Source: core/math/shapes/Circle.js

var Rectangle = require('./Rectangle'),
    CONST = require('../../const');

/**
 * The Circle object can be used to specify a hit area for displayObjects
 *
 * @class
 * @memberof PIXI
 * @param x {number} The X coordinate of the center of this circle
 * @param y {number} The Y coordinate of the center of this circle
 * @param radius {number} The radius of the circle
 */
function Circle(x, y, radius)
{
    /**
     * @member {number}
     * @default 0
     */
    this.x = x || 0;

    /**
     * @member {number}
     * @default 0
     */
    this.y = y || 0;

    /**
     * @member {number}
     * @default 0
     */
    this.radius = radius || 0;

    /**
     * The type of the object, mainly used to avoid `instanceof` checks
     *
     * @member {number}
     */
    this.type = CONST.SHAPES.CIRC;
}

Circle.prototype.constructor = Circle;
module.exports = Circle;

/**
 * Creates a clone of this Circle instance
 *
 * @return {PIXI.Circle} a copy of the Circle
 */
Circle.prototype.clone = function ()
{
    return new Circle(this.x, this.y, this.radius);
};

/**
 * Checks whether the x and y coordinates given are contained within this circle
 *
 * @param x {number} The X coordinate of the point to test
 * @param y {number} The Y coordinate of the point to test
 * @return {boolean} Whether the x/y coordinates are within this Circle
 */
Circle.prototype.contains = function (x, y)
{
    if (this.radius <= 0)
    {
        return false;
    }

    var dx = (this.x - x),
        dy = (this.y - y),
        r2 = this.radius * this.radius;

    dx *= dx;
    dy *= dy;

    return (dx + dy <= r2);
};

/**
* Returns the framing rectangle of the circle as a Rectangle object
*
* @return {PIXI.Rectangle} the framing rectangle
*/
Circle.prototype.getBounds = function ()
{
    return new Rectangle(this.x - this.radius, this.y - this.radius, this.radius * 2, this.radius * 2);
};