code: function(viewPortPx) {
          var layerPx = null;
          if (viewPortPx != null) {
              var dX = -this.layerContainerOriginPx.x;
              var dY = -this.layerContainerOriginPx.y;
              layerPx = viewPortPx.add(dX, dY);
              if (isNaN(layerPx.x) || isNaN(layerPx.y)) {
                  layerPx = null;
              }
          }
          return layerPx;
      }
docs: APIMethod: getLayerPxFromViewPortPx
  
  Parameters:
  viewPortPx - {<OpenLayers.Pixel>}
  
  Returns:
  {<OpenLayers.Pixel>} ViewPort Pixel translated into Layer Pixel
  coordinates