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 LSYSTEM(1)                                                       LSYSTEM(1)




 NAME
      lsystem - L system fractal generator

 SYNOPSIS
      lsystem [options] [file]

 DESCRIPTION
      lsystem is a fractal generator is based on the scheme devised by
      Aristid Lindenmayer (the L in Lsystem).  It is a so-called string-
      rewriting system, in which an input string is altered according to a
      set of transform rules.  The characters that make up the string, in
      turn, can represent commands to a "turtle" which will draw the actual
      fractal.  More sophisticated Lsystem incarnations have been used to
      create very lifelike renderings of plants (see "The Algorithmic Beauty
      of Plants", written by Prusinkiewicz and Lindenmayer, published by
      Springer Verlag).

      Here's an example of a string-rewriting system.  Consider the initial
      condition: b And the rules are: a = ab b = a Here are the results of 5
      passes through the string-rewriting engine: b (initial) a ab aba abaab
      abaababa If "a" and "b" represented commands to a turtle-like drawing
      routine, the output string "abaababa" could be fed to it, and it would
      generate some type of figure.

 OPTIONS
      -o file
              Write output to file.

      -s      Print string length info.

      -v      Print version info.

 OPERATION
      lsystem reads an L system description from the specified file and
      writes drawing commands on the standard output (or a file, if
      specified with the -o option).  These drawing commands should be piped
      through to convert them to the graphics driver of your choice.

      The drawing commands are generated in two phases: the string-rewriting
      phase, in which the initial string is iterated using a set of rules,
      and the string-interpretation phase, where the iterated string is
      passed to a `turtle' which substitutes macro definitions and executes
      drawing commands.

 INPUT FORMAT
      The input to lsystem consists of an initialization statement and
      several statements defining macros and rules.  Blank lines are
      ignored, and anything from a # to end-of-line is a comment.  The
      initialization statement has the format init <string> <iterations>
      <angle> where <string> is the initial string to be iterated,
      <iterations> is the number of iterations to perform, and <angle> is



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 LSYSTEM(1)                                                       LSYSTEM(1)




      the angle through which the turtle turns when given the appropriate
      command.  Strings in lsystem may consist of the letters A-Z (upper or
      lower case), +, -, [ and ].  Several of these have special meanings to
      the turtle, described later.

 MACROS
      Macros are useful to help simplify the design of fractals.  They are
      only used during the string-interpretation phase, when the turtle is
      in operation.  The format for defining a macro is <char> = <string>
      When the turtle is drawing, each occurrence of <char> is replaced
      (once only) by <string>.

 RULES
      Rules specify what replacements are done in the string in the
      iteration phase.  In each iteration, rules are applied to the string
      in the order they were defined in the input.  The format of a rule
      definition is <char> -> <string> Each instance of <char> in the string
      is replaced by <string>.

 TURTLE COMMANDS
      The turtle understands a limited set of commands.  If it encounters a
      foreign character, it simply ignores it.  This can be useful for
      building up complex strings.

      F       Move turtle forward one step.  A line is drawn.

      f       Move turtle forward one step.  No line is drawn.

      +       Turn turtle clockwise by the angle increment.

      -       Turn turtle anticlockwise by the angle increment.

      [       Stack turtle state.  This includes position, heading and
              current colour (see COLOURS, below).

      ]       Unstack turtle state.  The state is restored to the matching
              [.  No line is drawn if the turtle position changes.

 COLOURS
      You can change the colour of parts of the drawing (on those graphics
      devices which support colour) by setting characters to different
      colour values.  In the string-interpretation phase, when the turtle
      sees a character, the current colour is set to its corresponding
      colour.  If the character has no colour, no colour change is done.
      The format of a colour command is col <char> <red> <green> <blue> This
      sets <char> to have the specified RGB values.  The RGB values are in
      the range [0-1].

 RESTRICTIONS
      Complex rules and/or high iteration factors will take awhile to run
      through the lsystem engine.  The string may become larger than



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 LSYSTEM(1)                                                       LSYSTEM(1)




      available memory, too.  Each pass through the lsystem engine can
      produce an exponential increment in the length of the string, so ANY
      amount of memory will be filled.

 FILES
      tab(@);
      l l .
      %%LIBDIR%%@Example L systems

 HISTORY
      This implementation of L systems is based on (and uses the same
      examples from) an Atari ST version written by Mark Kimball (1991).

 SEE ALSO
 AUTHOR
      Glenn Hutchings (zondo@hunting2.demon.co.uk)






































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