/**
   * Draws an arrow on the given Graphics2D context
   * @param g The Graphics2D context to draw on
   * @param x The x location of the "tail" of the arrow
   * @param y The y location of the "tail" of the arrow
   * @param xx The x location of the "head" of the arrow
   * @param yy The y location of the "head" of the arrow
   */
  private void drawArrow( Graphics2D g, int x, int y, int xx, int yy )
  {
    float arrowWidth = 10.0f ;
    float theta = 0.423f ;
    int[] xPoints = new int[ 3 ] ;
    int[] yPoints = new int[ 3 ] ;
    float[] vecLine = new float[ 2 ] ;
    float[] vecLeft = new float[ 2 ] ;
    float fLength;
    float th;
    float ta;
    float baseX, baseY ;

    xPoints[ 0 ] = xx ;
    yPoints[ 0 ] = yy ;

    // build the line vector
    vecLine[ 0 ] = (float)xPoints[ 0 ] - x ;
    vecLine[ 1 ] = (float)yPoints[ 0 ] - y ;

    // build the arrow base vector - normal to the line
    vecLeft[ 0 ] = -vecLine[ 1 ] ;
    vecLeft[ 1 ] = vecLine[ 0 ] ;

    // setup length parameters
    fLength = (float)Math.sqrt( vecLine[0] * vecLine[0] + vecLine[1] * vecLine[1] ) ;
    th = arrowWidth / ( 2.0f * fLength ) ;
    ta = arrowWidth / ( 2.0f * ( (float)Math.tan( theta ) / 2.0f ) * fLength ) ;

    // find the base of the arrow
    baseX = ( (float)xPoints[ 0 ] - ta * vecLine[0]);
    baseY = ( (float)yPoints[ 0 ] - ta * vecLine[1]);

    // build the points on the sides of the arrow
    xPoints[ 1 ] = (int)( baseX + th * vecLeft[0] );
    yPoints[ 1 ] = (int)( baseY + th * vecLeft[1] );
    xPoints[ 2 ] = (int)( baseX - th * vecLeft[0] );
    yPoints[ 2 ] = (int)( baseY - th * vecLeft[1] );

    g.drawLine( x, y, (int)baseX, (int)baseY ) ;
    g.fillPolygon( xPoints, yPoints, 3 ) ;
  }