The project contains classes for drawing three types of curves:

• logarithmic spiral (log.l file)
• lissajous curve (lissajous.l file)
• butterfly curve (butterfly.l file)

The project illustrates how a program code can be divided into a small pieces of code stored in separate files. Open and run the code from the app.l file. The code is quite short: it creates an object of a selected type of curve and sliders based on parameters described in that curve class. Curve classes themselves are coded in separate files and attached to the main app with use of the include instruction.

Code splitted into many files, each containing description of one class, is more readable and easy to handle. Try to add your own curve class on basis of one of the provided classes. The following rules should be preserved:

• the new curve class inherits from curve class: use curve :c
• there is a single argument to the constructor: the curve color;
• any parameters of the new curve should be defined in the following way:

  :param,"name := {p₀ p_min p_max step}

  "name - parameter name (word)
  p0 - initial value, from the range < pmin; pmax >
  pmin - lower limit of parameter values
  pmax - upper limit of parameter values
  step - step in the value when it is changed with a slider (value is continuous if step is omitted)
• the new class has fn function defined; it is responsible for the curve drawing.

Each file with a curve definition has to include the file with the base class definition. To avoid unneccessary, multiple includes, use:

if not defined? "curve [include "curve.l]

The base class contains the fn prototype and all the code neccessary for the curve repainting after the graphics window size or scale changes. It also handles changes of the curve parameters.

As an excersise you may add to the project the following class of the asteroid curve:

to asteroid :c
  use curve :c
  to fn
    pu setxy :s 0 pd
    for [t 0 360] [
      if :stop [stop]
      let "x :s * (cos :t)^:k
      let "y :s * (sin :t)^:k
      setxy :x :y
    ]
  end

  :param,"K := {3 1 13 2}
  :param,"S := {150 10 300 1}
end