Compucolor.org – Virtual Media

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DRAW WITH JOYSTICK
	===========================================

	by Myron T. Steffy, Sun City, Arizona 85351

The program 'DRAW' will allow you to draw straight  lines  on
the screen with either a joystick or  the  number  keys.   It
employs the 'Plot  242'  vector  function  of  Compucolor  II
which essentially connects two  points  on  the  screen  with
the shortest line.

The direction of travel is similar to  the  way  the  numeric
keypad ia arranged.  That is, '8' = north, '2' =  south,  '4'
and  '6'  =  west  and  east  respectively.   Depressing  two
adjacent direction keys  at  the  same  time  or  moving  the
joystick to a diagonal position  will  give  you  a  diagonal
line.  The center key, '5', erases the screen and  plots  the
starting location, the  exact  center  of  the  screen.   The
letter 'D' will exit to FCS control and 'ESC I' will re-enter.

All eight color keys are active and  black  may  be  used  to
erase or black out  a  line  that  you  have  already  drawn.
When you change colors, the  start  and  end  points  of  the
line are identical.  Since the resolution of the  'Plot  242'
mode is only 128 by 128, the points and  lines  produced  are
rather coarse.

The method is similar to that described by Steve  Perrigo  in
a recent issue  of  'FORUM'  (Vol.  2,  No.  1)  except  that
machine language  is  used  to  speed  up  the  process.   It
succeeds so well that a delay loop, 'WATL', is  necessary  to
slow it down.  You may slow it down still  more  by  changing
the '1' at A148H to a larger number.  For you guys  with  the
super  fast  reflexes,  change  'WATL'  to  'WATS'   in   the
subroutine 'PRINT'.  Since WATL gives you  a  20  millisecond
delay for each count in the 'A' register  and  WATS  only  .5
millisecond, the increase  is  a  factor  of  40.   You  will
probably have to make it loop several  times,  controlled  by
the number you stick into the 'A' register.

To preserve your artwork, you might have  a  routine  set  up
in Basic to 'Save' the screen display to  a  disc  for  later
recall.  There is at  least  one  library  program  available
for that purpose.  As usual, have fun!