FUNCTION SL_FILL()

  Short:
  ------
  SL_FILL() Fills a rectangle with shading or a pattern.

  Returns:
  --------
  cCode => control string to send to the printer

  Syntax:
  -------
  SL_FILL(nTop,nLeft,nBottom,nRight,[cShade],[cFill],[nCpi],[nLpi])

  Description:
  ------------
  Fills a rectangle based on rows and columns at
  <nTop,nLeft> to <nBottom,nRight>. The area may be shaded
  [cShade] or filled with a pattern [cFill] :

  The shading percentages are (default "20") :

         "1 thru 2" = 2% shade
        "3 thru 10" = 10% shade
       "11 thru 20" = 20% shade
       "21 thru 35" = 30% shade
       "36 thru 55" = 45% shade
       "56 thru 80" = 70% shade
       "81 thru 99" = 90% shade
              "100" = 100% shade

  The pattern fills are (default "6"):

       "1" = horizontal lines
       "2" = vertical lines
       "3" = diagonal lines top right to bottom left
       "4" = diagonal lines top left to bottom right
       "5" = #1 and # 2 combined
       "6" = #3 and # 4 combined

  <nCpi> is the characters per inch, and defaults to
  10. <nLpi> is the lines per inch, and defaults to 6.

  Examples:
  ---------
   SL_FILL(10,10,20,20,"50")
    // fills from 10,10 to 20 20 with 50% shading

  Notes:
  -------
  Does not send anything to the printer - instead
  returns a control string that you send to the printer. String can be
  sent with ? or ?? or  QOUT() or QQOUT().

  For HP and compatible(PCL) Laserjet printers.

  Source:
  -------
  S_HPLAS.PRG