var _w =  _x0 * _pv[3] + _y0 * _pv[7] + _z0 * _pv[11] + _pv[15];
if (_w > 0) {
    var _x = (_x0 * _pv[0] + _y0 * _pv[4] + _z0 * _pv[8]  + _pv[12]) / abs(_w);
    var _y = (_x0 * _pv[1] + _y0 * _pv[5] + _z0 * _pv[9]  + _pv[13]) / abs(_w);
    _x = _half_port_width + _x * _half_port_width;
    _y = _half_port_height - _y * _half_port_height;
}