content: // ===============================================================================
  // Authors: AFRL/RQQD
  // Organization: Air Force Research Laboratory, Aerospace Systems Directorate, Power and Control Division
  // 
  // Copyright (c) 2017 Government of the United State of America, as represented by
  // the Secretary of the Air Force.  No copyright is claimed in the United States under
  // Title 17, U.S. Code.  All Other Rights Reserved.
  // ===============================================================================
  
  package org.flexdock.plaf.common.border;
  
  import java.awt.Color;
  import java.awt.Component;
  import java.awt.Graphics;
  import java.awt.Insets;
  
  import javax.swing.border.Border;
  
  
  public class ShadowBorder implements Border {
      private Insets insets;
  
      public ShadowBorder() {
          insets = new Insets(1, 1, 3, 3);
      }
  
      public Insets getBorderInsets(Component c) {
          return insets;
      }
  
      public boolean isBorderOpaque() {
          // we'll be filling in our own background.
          return true;
      }
  
      public void paintBorder(Component c, Graphics g, int x,
                              int y, int w, int h) {
          // choose which colors we want to use
          Color bg = c.getBackground();
          if(c.getParent()!=null)
              bg = c.getParent().getBackground();
          Color mid = bg.darker();
          Color rect = mid.darker();
          Color edge = average(mid, bg);
  
          // fill in the corners with the parent-background
          // so it looks see-through
          g.setColor(bg);
          g.fillRect(0, h-3, 3, 3);
          g.fillRect(w-3, 0, 3, 3);
          g.fillRect(w-3, h-3, 3, 3);
  
          // draw the outline
          g.setColor(rect);
          g.drawRect(0, 0, w - 3, h - 3);
  
          // draw the drop-shadow
          g.setColor(mid);
          g.drawLine(1, h - 2, w - 2, h - 2);
          g.drawLine(w - 2, 1, w - 2, h - 2);
  
          g.setColor(edge);
          g.drawLine(2, h - 1, w - 2, h - 1);
          g.drawLine(w - 1, 2, w - 1, h - 2);
      }
  
      private static Color average(Color c1, Color c2) {
          int red = c1.getRed() + (c2.getRed() - c1.getRed()) / 2;
          int green = c1.getGreen() + (c2.getGreen() - c1.getGreen()) / 2;
          int blue = c1.getBlue() + (c2.getBlue() - c1.getBlue()) / 2;
          return new Color(red, green, blue);
      }
  }