% draw(Size)
% draws a graphics with a given Size
draw(Size) :-
   % prepare a Display to draw the object on
   % generate a new display name
   gensym(w,Display),
   free('@'Display),
   % define size of the display (picture size + scroll bar area)
   SizeD is Size+20,
   % create a new display and open it
   new('@'Display,picture('*** Your picture''s name ***',size(SizeD,SizeD))),
   send('@'Display,background,colour(black)),
   send('@'Display,open),
   % draw the object on the display
   draw_object('@'Display,Size,Size).

% draw_object(Display,Size,CurrentSize,*** add additional parameters here, if needed ***)
% draws a gradient graphics of size Size into Display
% CurrentSize is decreased recursively fom Size to 0
draw_object(_,_,0, *** add additional parameters here, if needed ***).
draw_object(Name,Size,CSize, *** add additional parameters here, if needed ***) :-

  % *** insert the computation of graphical parameters here ***

  % *** create and draw the current graphical object here ***

  % *** send all additional parameters to the current graphical object ***

  % decrement CurrentSize and call draw_object recursively
  CSizeNew is CSize - 2,
  draw_object(Name,Size,CSizeNew),
   % if desired save the display as .jpg
   write_ln('Save the graphics (y/n): '),
   get_single_char(A),
   pu_code(A),nl,
   A=:=121 ->
     (write_ln('enter file name: '),
      read_line_to_codes(user,X),
      atom_codes(File,X),
      atom_concat(File,'.jpg',FileName),
      get('@'Display,image,Image),
      send(Image,save,FileName,jpeg) ).


% Call the program and see the result
:- draw(*** specify desired display size here ***).