function Wall(options) {
    Particle.call(this, options);

    var n = this.normal = new Vec3();

    var d = this.direction = options.direction;
    switch (d) {
        case Wall.DOWN:
            n.set(0, 1, 0);
            break;
        case Wall.UP:
            n.set(0, -1, 0);
            break;
        case Wall.LEFT:
            n.set(-1, 0, 0);
            break;
        case Wall.RIGHT:
            n.set(1, 0, 0);
            break;
        case Wall.FORWARD:
            n.set(0, 0, -1);
            break;
        case Wall.BACKWARD:
            n.set(0, 0, 1);
            break;
        default:
            break;
    }

    this.invNormal = Vec3.clone(n, new Vec3()).invert();

    this.mass = Infinity;
    this.inverseMass = 0;

    this.type = 1 << 3;
}
An axis-aligned boundary. Will not respond to forces or impulses.

@class Wall
@extends Particle
@param {Object} options The initial state of the body.