PRINTING HERCULES GRAPHICS SCREENS WITH QUICKBASIC 4.0
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          To fully  understand how to print graphics screens generated
          by Hercules  and fully  compatible graphics  adapters, it is
          necessary to  understand how Hercules graphics memory is set
          up.
          
          Hercules  memory  starts  at  hex  paragraph  B000  (decimal
          45056).   Graphics memory  starts  with  page  zero  at  hex
          paragraph B000  (45056), and  page  one  at  hex  para-graph
          B800 (47104) which  is B000H  + 800H,  or a 32K page (800H *
          10H =  8000H or  32768).   However, graphics  memory is  not
          contiguous memory,  as we  will see  later.   Each  line  of
          pixels on  both pages of screen mode 3 consists of 90 bytes.
          Thus, the  top line  of pixels  on page zero (B000) would go
          from B000  + 0  to B000  + 59  (45056 + 89).  To draw a line
          from the  upper left corner of the screen to the upper right
          corner of  the screen on page zero, we would simply POKE 255
          into positions 0 through 89 (255 = all 8 bits per byte being
          "on"):
          
          SCREEN 3
          DEF SEG = &HB000
          
          FOR x = 0 TO 89              ' B000H:0000H to B000H:0059H
             POKE x, 255
          NEXT x
          
          To do the same thing on page one, simply change the value of
          the DEF SEG statement to &HB800 (B000H + 800H).
          
          However, the  graphics memory  is not  contiguous.    If  we
          continue to  draw at  B000H + 5AH, the next line will appear
          three lines down from the first.  In order to draw a line on
          the second  line, we  must add  2000H to  the address of the
          first byte on the first line:
          
          FOR x = 8192 TO 8281        ' B000H:2000H to B000H:2059H
             POKE x, 255
          NEXT x
          
          This must  also be done for line three and line four.  Thus,
          the first  byte of  line three  would be B000H:4000H and the
          first byte  of the  fourth line  would be  B000H:6000H.  The
          first byte  of line  five would  be B000H:005AH (45056:0090)
          and so  on for  every four  lines down the screen.  The same
          applies for  page one.   Please  see the  figure on page  89
          of "The Programmer's Guide to PC and PS/2 Video Systems", by
          Richard Wilton [Microsoft Press, 1987] for a diagram of  the
          Hercules video buffer in graphics mode.

          The listings  included in  this  archive  print  a  Hercules
          graphics screen (page zero) to either an Epson or compatible
          printer, or  an HP  LaserJet family  printer.  If you have a
          different printer,  you will  need  to  change  the  printer
          commands for setting line spacing and graphics mode for your
          printer.   To print page one, add 800H (2048) to the DEF SEG
          statement.