GameLib.D3.Vector4 = function(x, y, z, w) {

    this.x = 0;
    this.y = 0;
    this.z = 0;
    this.w = 0;

    if (x) {
        this.x = x;
    }

    if (y) {
        this.y = y;
    }

    if (z) {
        this.z = z;
    }

    if (w) {
        this.w = w;
    }
};

GameLib.D3.Vector4.prototype.translate = function (v) {
    this.x += v.x;
    this.y += v.y;
    this.z += v.z;
    return this;
};

GameLib.D3.Vector4.prototype.copy = function () {
    return new GameLib.D3.Vector4(
        this.x,
        this.y,
        this.z,
        this.w
    );
};

GameLib.D3.Vector4.prototype.multiply = function (s) {
    if (s instanceof GameLib.D3.Vector3) {
        this.x *= s.x;
        this.y *= s.y;
        this.z *= s.z;
    } else if (s instanceof GameLib.D3.Matrix4) {
        var x = s.rows[0].x * this.x + s.rows[0].y * this.y + s.rows[0].z * this.z + s.rows[0].w * this.w;
        var y = s.rows[1].x * this.x + s.rows[1].y * this.y + s.rows[1].z * this.z + s.rows[1].w * this.w;
        var z = s.rows[2].x * this.x + s.rows[2].y * this.y + s.rows[2].z * this.z + s.rows[2].w * this.w;
        var w = s.rows[3].x * this.x + s.rows[3].y * this.y + s.rows[3].z * this.z + s.rows[3].w * this.w;
        this.x = x;
        this.y = y;
        this.z = z;
        this.w = w;
    } else {
        console.log("functionality not implemented - please do this");
        throw new Error("not implemented");
    }
};


GameLib.D3.Vector4.prototype.normalize = function () {

    // note - leave w untouched
    var EPSILON = 0.000001;

    var v2 = this.x * this.x + this.y * this.y + this.z * this.z;

    if (v2 < EPSILON) {
        return this; //do nothing for zero vector
    }

    var invLength = 1 / Math.sqrt(v2);

    this.x *= invLength;
    this.y *= invLength;
    this.z *= invLength;

    return this;
};

GameLib.D3.Vector4.prototype.subtract = function (v) {

    if (v instanceof GameLib.D3.Vector3) {
        this.x -= v.x;
        this.y -= v.y;
        this.z -= v.z;
    }

    if (v instanceof GameLib.D3.Vector4) {
        this.x -= v.x;
        this.y -= v.y;
        this.z -= v.z;
        this.w -= v.w;
    }

    return this;
};