FRACTINT conventions

 

For reference, here are the complete list of FRACTINT L-system symbols. This is extracted mainly from the FRACTINT online manual. We assume a unit length d and a standard angle increment has been established, which must be of the form where n is a positive integer. The standard drawing commands are:

F:

Draw forward one unit.

G:

Move forward one unit (without drawing).

+:

Increase angle by counterclockwise.

-:

Decrease angle by clockwise.

|:

Try to turn 180 degrees. (If n is odd, where , the turn will be the largest possible turn less than 180 degrees which is a multiple of .)

The above commands are especially fast because the angles are restricted to multiples of . However, if it is required to turn at more general angles, one may use the following commands which keep a completely separate angle pointer specified in degrees.

D:

Draw forward one unit.

M:

Move forward one unit (without drawing).

:

Increase angle nn degrees counterclockwise.

/nn:

Decrease angle nn degrees clockwise.

These are the commands for changing colors based on the current FRACTINT color map. The color map associates different colors to a sequence of positive integers. FRACTINT has builtin procedures for changing color maps.

Cnn:

Select color nn

<nn:

Increment color by nn

>nn:

Decrement color by nn

These are the bracketing commands for modelling branched structures. We will give some examples in the next section.

:

``Push:'' This stores the current position and heading on a memory stack.

:

``Pop:'' This causes the ``turtle'' to return to the last position and heading stored on the memory stack. It ``pops'' this position off the stack.

!:

Reverse directions (Switch meanings of +, -, / and )

@nnn:

Multiply line segment size d by scale factor nnn. The new size will be in effect until another @ command. nnn may be a plain number, or may be preceded by I for inverse, or Q for square root. For instance, @I2 gives a factor of 1/2, @Q2 gives , and @IQ2 gives .

The last two commands coupled with the pop and push commands can achieve very elaborate branching structures.