The routine plpat can be used to set the area fill pattern.  The
      pattern consists of 1 or 2 sets of parallel lines with specified
      inclinations and spacings.  The arguments to this routine are the
      number of sets to use (1 or 2) followed by two pointers to integer
      arrays (of 1 or 2 elements) specifying the inclinations in tenths of
      a degree and the spacing in micrometers (the inclination should be
      between -900 and 900).  Thus to specify an area fill pattern
      consisting of horizontal lines spaced 2 mm apart use:
    
|     *inc = 0;
    *del = 2000;
    plpat(1, inc, del); | 
To set up a symmetrical crosshatch pattern with lines directed 30 degrees above and below the horizontal and spaced 1.5 mm apart use:
|     *inc = 300;
    *(inc+1) = -300;
    *del = 1500;
    *(del+1) = 1500;
    plpat(2, inc, del); | 
      The routine plpsty can be used to select from 1 of 8 predefined
      patterns.
    
The area fill routines also use the current line style, width and colors to give a virtually infinite number of different patterns.