internal static Rect clampToScreen (Rect rect)
{
rect.width = Mathf.Clamp (rect.width, 0, Screen.width);
rect.height = Mathf.Clamp (rect.height, 0, Screen.height);
rect.x = Mathf.Clamp (rect.x, 0, Screen.width - rect.width);
rect.y = Mathf.Clamp (rect.y, 0, Screen.height - rect.height);
return rect;
}