p2s/src/shapes/Circle.js

A JavaScript 2D physics engine.

var Shape = require('./Shape')
,    vec2 = require('../math/vec2')
,    shallowClone = require('../utils/Utils').shallowClone;

module.exports = Circle;

/**
 * Circle shape class.
 * @class Circle
 * @extends Shape
 * @constructor
 * @param {options} [options] (Note that this options object will be passed on to the {{#crossLink "Shape"}}{{/crossLink}} constructor.)
 * @param {number} [options.radius=1] The radius of this circle
 *
 * @example
 *     var body = new Body({ mass: 1 });
 *     var circleShape = new Circle({
 *         radius: 1
 *     });
 *     body.addShape(circleShape);
 */
function Circle(options){
    options = options ? shallowClone(options) : {};

    /**
     * The radius of the circle.
     * @property radius
     * @type {number}
     */
    this.radius = options.radius !== undefined ? options.radius : 1;

    options.type = Shape.CIRCLE;
    Shape.call(this, options);
}
Circle.prototype = new Shape();
Circle.prototype.constructor = Circle;

/**
 * @method computeMomentOfInertia
 * @return {Number}
 */
Circle.prototype.computeMomentOfInertia = function(){
    var r = this.radius;
    return r * r / 2;
};

/**
 * @method updateBoundingRadius
 * @return {Number}
 */
Circle.prototype.updateBoundingRadius = function(){
    this.boundingRadius = this.radius;
};

/**
 * @method updateArea
 * @return {Number}
 */
Circle.prototype.updateArea = function(){
    this.area = Math.PI * this.radius * this.radius;
};

/**
 * @method computeAABB
 * @param  {AABB}   out      The resulting AABB.
 * @param  {Array}  position
 * @param  {Number} angle
 */
Circle.prototype.computeAABB = function(out, position/*, angle*/){
    var r = this.radius;
    vec2.set(out.upperBound,  r,  r);
    vec2.set(out.lowerBound, -r, -r);
    if(position){
        vec2.add(out.lowerBound, out.lowerBound, position);
        vec2.add(out.upperBound, out.upperBound, position);
    }
};

var Ray_intersectSphere_intersectionPoint = vec2.create();
var Ray_intersectSphere_normal = vec2.create();

/**
 * @method raycast
 * @param  {RaycastResult} result
 * @param  {Ray} ray
 * @param  {array} position
 * @param  {number} angle
 */
Circle.prototype.raycast = function(result, ray, position/*, angle*/){
    var from = ray.from,
        to = ray.to,
        r = this.radius;

    var a = Math.pow(to[0] - from[0], 2) + Math.pow(to[1] - from[1], 2);
    var b = 2 * ((to[0] - from[0]) * (from[0] - position[0]) + (to[1] - from[1]) * (from[1] - position[1]));
    var c = Math.pow(from[0] - position[0], 2) + Math.pow(from[1] - position[1], 2) - Math.pow(r, 2);
    var delta = Math.pow(b, 2) - 4 * a * c;

    var intersectionPoint = Ray_intersectSphere_intersectionPoint;
    var normal = Ray_intersectSphere_normal;

    if(delta < 0){
        // No intersection
        return;

    } else if(delta === 0){
        // single intersection point
        vec2.lerp(intersectionPoint, from, to, delta);

        vec2.subtract(normal, intersectionPoint, position);
        vec2.normalize(normal,normal);

        ray.reportIntersection(result, delta, normal, -1);

    } else {
        var sqrtDelta = Math.sqrt(delta);
        var inv2a = 1 / (2 * a);
        var d1 = (- b - sqrtDelta) * inv2a;
        var d2 = (- b + sqrtDelta) * inv2a;

        if(d1 >= 0 && d1 <= 1){
            vec2.lerp(intersectionPoint, from, to, d1);

            vec2.subtract(normal, intersectionPoint, position);
            vec2.normalize(normal,normal);

            ray.reportIntersection(result, d1, normal, -1);

            if(result.shouldStop(ray)){
                return;
            }
        }

        if(d2 >= 0 && d2 <= 1){
            vec2.lerp(intersectionPoint, from, to, d2);

            vec2.subtract(normal, intersectionPoint, position);
            vec2.normalize(normal,normal);

            ray.reportIntersection(result, d2, normal, -1);
        }
    }
};

Circle.prototype.pointTest = function(localPoint){
    var radius = this.radius;
    return vec2.squaredLength(localPoint) <= radius * radius;
};