p2s/src/shapes/Line.js

A JavaScript 2D physics engine.

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

module.exports = Line;

/**
 * Line shape class. The line shape is along the x direction, and stretches from [-length/2, 0] to [length/2,0].
 * @class Line
 * @param {object} [options] (Note that this options object will be passed on to the {{#crossLink "Shape"}}{{/crossLink}} constructor.)
 * @param {Number} [options.length=1] The total length of the line
 * @extends Shape
 * @constructor
 * @example
 *     var body = new Body();
 *     var lineShape = new Line({
 *         length: 1
 *     });
 *     body.addShape(lineShape);
 */
function Line(options){
    options = options ? shallowClone(options) : {};

    /**
     * Length of this line
     * @property {Number} length
     * @default 1
     */
    this.length = options.length !== undefined ? options.length : 1;

    options.type = Shape.LINE;
    Shape.call(this, options);
}
Line.prototype = new Shape();
Line.prototype.constructor = Line;

Line.prototype.computeMomentOfInertia = function(){
    return Math.pow(this.length,2) / 12;
};

Line.prototype.updateBoundingRadius = function(){
    this.boundingRadius = this.length/2;
};

var points = [vec2.create(),vec2.create()];

/**
 * @method computeAABB
 * @param  {AABB}   out      The resulting AABB.
 * @param  {Array}  position
 * @param  {Number} angle
 */
Line.prototype.computeAABB = function(out, position, angle){
    var l2 = this.length / 2;
    vec2.set(points[0], -l2,  0);
    vec2.set(points[1],  l2,  0);
    out.setFromPoints(points,position,angle,0);
};

var raycast_normal = vec2.create();
var raycast_l0 = vec2.create();
var raycast_l1 = vec2.create();
var raycast_unit_y = vec2.fromValues(0,1);

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

    var l0 = raycast_l0;
    var l1 = raycast_l1;

    // get start and end of the line
    var halfLen = this.length / 2;
    vec2.set(l0, -halfLen, 0);
    vec2.set(l1, halfLen, 0);
    vec2.toGlobalFrame(l0, l0, position, angle);
    vec2.toGlobalFrame(l1, l1, position, angle);

    var fraction = vec2.getLineSegmentsIntersectionFraction(l0, l1, from, to);
    if(fraction >= 0){
        var normal = raycast_normal;
        vec2.rotate(normal, raycast_unit_y, angle); // todo: this should depend on which side the ray comes from
        ray.reportIntersection(result, fraction, normal, -1);
    }
};