Elses

A Java-based implementation of an L-System generator.

The Elses programming "language"

An example L-System "program":

AXIOM: F
F -> FF[[-FFF@]++FF@]

Supported instructions:

  F	  move pen forward and draw a line
  f	  move pen forward w/o drawing a line
  +	  turn left by default degrees
  -	  turn right by default degrees
  [	  push current state (x/y position, angle) on to the context stack
  ]	  pop context from stack and discard/replace current state (x/y postion, angle)
  @	  draw a 'dot' with a specified radius (default is 1/2 current line length) 

Building Elses

To build the Elses interpreter using Ant:

ant clean build

Running an Elses program

To run from the build directory:

java -cp dist org.hccp.elses.Elses

Options:

--angle,-a ANGLE	The angle to increment/decrement when interpreting '+' or
			'-' commands. A range of angle values can be given for the
 				interpreter to randomly chooose from at each step by using
 			the form of 'n-m'. For example the argument -a 20-35 would
 				allow the interpreter to choose values between 20 degrees
 			and 35 degrees at each step. The default value, if no
 				angle or range is passed via this argument, is 45 degrees.

--help,-h      Prints this message.

--iterations,-i ITERATIONS      The number of rule-application iterations.

--line-length,-l LINE_LENGTH	The length of each pen move 'F'. A range of
				line length values can be given for the
                              	interpreter to randomly chooose from at each
                              	step by using the form of 'n-m'. For example
                              	the argument -l 2-10 would allow the
                              	interpreter to choose values between 2 and 10
                              	at each step. If no line length is specified,
                              	a default line length of 10 will be used.

--x-position,-x INITIAL_X_POSITION      The initial x position from which to
    	                                begin drawing. The default is 150 (the
            	                        center point for a landscape-oriented A3
                    	                paper.

--y-position,-y INITIAL_Y_POSITION      The initial y position from which to
    	                                begin drawing. The default is 25.

--rotation ROTATION      The number of degrees to rotate the drawing after
                     initial rendering.

--dot-radius,-r DOT_RADIUS      The radius of the circle drawn by a '@' command.
    	                        If no radius is selected, a default radius of
            	                1/2 of the current line length will be used.

--width,-w WIDTH      Sets the width of the draw-able page to the provided
    	              value. The default is 291 as this matches the width of an
            	      A3 paper in portrait mode.

--height HEIGHT      Sets the height of the draw-able page to the provided
    	             value. The default is 420 as this matches the height of an
                     A3 paper in portrait mode.

Examples:

For a file, test-003.txt, that contains the following content:

AXIOM: F
F -> FF[[-FFF@]++FF@]

You can run the following command:

java -cp dist org.hccp.elses.Elses -i 2 -a 10 -r 5 -l 25 -x 150 -y 50 samples/test-003.txt /tmp/lsys-plot.svg

in order to generate an SVG like this:

A Koch curve

Program:

 AXIOM: F
 F -> F+F-F-F+F

Command line:

elses -i 3 -l 10 -a 90 --width 300 --height 200 -x 200 -y -40 --rotation 90 samples/koch.txt samples/koch.svg

A Sierpinski triangle

Program:

AXIOM: F-F-F
F -> F-f+F+f-F
f -> ff

Command line:

elses -i 4 -a 120 --width 200 --height 200 -x 70 -y 50 --rotation -150 samples/sierpinski.txt samples/sierpinski.svg

Credits:

A bunch of the parsing code and structure is derived from Lox and Robert Nystrom's wonderful book "Crafting Interpreters".