
  Help for HailStorm.
  """"""""""""""""""

  Summary:      <Menu> = Toggle 'Edit' mode ON/OFF.
              <Select> = Draw - various obstacles.
              <Adjust> = Delete - draw in background colour.

               '>'/'<' = Increase/Decrease 'hail' size.
        Up/Down arrows = +/- speed, but with -/+ density.
                 <Tab> = Re-start

  Introduction:
  """""""""""""
   The 'Falling Sand' problem seems to be a classic in computer
  graphics. The standard approach is via cellular automata and
  using compiled languages along with some heavy duty graphical
  libraries.

   This version uses a totally different method and is a good
  test of the speed of BASIC. It is also quite short.
   I chose to use a 'hail-storm' simply because it seemed more
  realitic than the usual 'sand falling from the sky'!
   No screen-bank switching is involved.

   When run the program will start in the 'active' (or ON) state
  of displaying just 'falling hail'.  The Pointer is Red.
  The only available mouse-key in this state is the <Menu> key.
   Pressing <Menu> stops the 'falling-hail' and enters the 'Edit'
  mode (or OFF state)- see below. The pointer turns Blue.
   Pressing <Menu> again will leave 'Edit' mode and re-start the
  previous 'falling-hail' mode (ON). (Pointer back to Red).

   So essentially <Menu> acts as an ON/OFF switch.

   The user can also change the size of the 'hail' - from fine
  to coarse.  The range is 3 to 8, and the default is 5.
  (Note that 3 is quite slow, and 8 is too fast.)

   This change will cause a full re-start.
   It is done using Keyboard keys < and >.

   See below for more Keyboard features


  'Edit' mode (OFF state):  Pointer turns Blue.
  """""""""""""""""""""""""""""""""""""""""""""

   In this mode the mouse <Select> and <Adjust> are now available.
   
   <Select> enables drawing on the screen. The pointer turns magenta.
  Obstacles can now be drawn - such as angled platforms for the hail
  to roll down and create conical piles on the ground. Any shapes,
  wiggles, trees etc can be drawn, even writing your own name!

   <Adjust> enables you to draw in 'background' colour i.e delete.  
  This means you can correct/amend your current drawing. The pointer
  now turns yellow.  You can also create new 'channels' to join
  existing 'background' areas - for the hail to fall through. Note
  that the top of the screen can be regarded as an infinite source
  of 'hail' - so you can create a 'channel' from the top of the
  screen to any other area you wish to 'fill' with hail.

   When you are satisfied with your 'drawing' just press <Menu> to
  return to 'active' mode. We are now back in the ON state i.e the
  hail will resume falling.

   You can of course enter 'Edit' mode as many times as you like.


  Keyboard keys:
  """"""""""""""

   '>' increases the size of the 'hail'.

   '<' decreases the size of the 'hail'.

    <Up-Arrow> increases the speed but decreases the density.

    <Down-Arrow> decreases the speed but increases the density.

    <Tab> clears the current screen.

   NOTE: all the above will restart the display.

    Holding down other keys pauses the display. Release to continue.


  Copyright: R.A.Swetman



  