static void Init()
 {
     if (m_window == null)
     {
         m_window = ( LightmapViewer )EditorWindow.GetWindow(typeof(LightmapViewer), false, "Lightmap Viewer");
     }
     m_window.minSize  = new Vector2(400, 300);
     m_window.position = new Rect(0, 0, m_window.minSize.x, m_window.minSize.y);
     m_window.Show();
 }
 void OnDestroy()
 {
     m_window = null;
 }