static function getPoint($x, $y, Camera $camera, $screenWidth, $screenHeight)
{
$recenterX = ($x - $screenWidth / 2.0) / 2.0 / $screenWidth;
$recenterY = -($y - $screenHeight / 2.0) / 2.0 / $screenHeight;
$a = Vector::times($recenterX, $camera->right);
$b = Vector::times($recenterY, $camera->up);
$c = Vector::plus($a, $b);
return Vector::norm(Vector::plus($camera->forward, $c));
}