code: protected void updateLayerActivity(WorldWindow wwd)
      {
          for (GeneralLayerPanel layerPanel : this.layerPanels)
          {
              // The frame timestamp from the layer indicates the last frame in which it rendered something. If that
              // timestamp matches the current timestamp of the scene controller, then the layer rendered something
              // during the most recent frame. Note that this frame timestamp protocol is only in place by default
              // for TiledImageLayer and its subclasses. Applications could, however, implement it for the layers
              // they design.
  
              Long layerTimeStamp = (Long) layerPanel.getLayer().getValue(AVKey.FRAME_TIMESTAMP);
              Long frameTimeStamp = (Long) wwd.getSceneController().getValue(AVKey.FRAME_TIMESTAMP);
  
              if (layerTimeStamp != null && frameTimeStamp != null
                  && layerTimeStamp.longValue() == frameTimeStamp.longValue())
              {
                  // Set the font to bold if the layer was just rendered.
                  layerPanel.setLayerNameFont(this.boldFont);
              }
              else if (layerPanel.getLayer() instanceof TiledImageLayer)
              {
                  // Set the font to plain if the layer was not just rendered.
                  layerPanel.setLayerNameFont(this.plainFont);
              }
              else if (layerPanel.getLayer().isEnabled())
              {
                  // Set enabled layer types other than TiledImageLayer to bold.
                  layerPanel.setLayerNameFont(this.boldFont);
              }
              else if (!layerPanel.getLayer().isEnabled())
              {
                  // Set disabled layer types other than TiledImageLayer to plain.
                  layerPanel.setLayerNameFont(this.plainFont);
              }
          }
      }
docs: Loops through this layer panel's layer/checkbox list and updates the checkbox font to indicate whether the
  corresponding layer was just rendered. This method is called by a rendering listener -- see comment below.
  
  @param wwd the world window.