Dragon curve

Programs to create dragon curves a fractal object.

Logo

to dragon :step :length
dcr :step :length
end

to dcr :step :length
make "step :step - 1
make "length :length / 1.41421
if :step > 0 [rt 45 dcr :step :length lt 90 dcl :step :length rt 45]
if :step = 0 [rt 45 fd :length lt 90 fd :length rt 45]
end

to dcl :step :length
make "step :step - 1
make "length :length / 1.41421
if :step > 0 [lt 45 dcr :step :length rt 90 dcl :step :length lt 45]
if :step = 0 [lt 45 fd :length rt 90 fd :length lt 45]
end

The program can be started using dcr 4 300 or dcl 4 300.

An alternative approach by using sentence-like grammar using four productions o->on, n->wn, w->ws, s->os. O, S, N and W mean cardinal points.

to O :step :length
if :step=1 [Rt 90 fd :length Lt 90] [O (:step - 1) (:length / 1.41421) N (:step - 1) (:length / 1.41421)]
end

to N :step :length
if :step=1 [fd :length] [W (:step - 1) (:length / 1.41421) N (:step - 1) (:length / 1.41421)]
end

to W :step :length
if :step=1 [Lt 90 fd :length Rt 90] [W (:step - 1) (:length / 1.41421) S (:step - 1) (:length / 1.41421)]
end 

to S :step :length
if :step=1 [Rt 180 fd :length Lt 180] [O (:step - 1) (:length / 1.41421) S (:step - 1) (:length / 1.41421)]
end

This page uses content from Wikipedia. The original article was at Drachenkurve. The list of authors can be seen in the page history. As with Rosetta Code, the text of Wikipedia is available under the GNU FDL. (See links for details on variance)

Pascal

using Compas (Pascal with Logo-expansion):

procedure dcr(step,dir:integer;length:real);
 begin;
  step:=step -1;
  length:= length/sqrt(2);
  if dir > 0 then
   begin
     if step > 0 then
     begin
       turnright(45);
       dcr(step,1,length);
       turnleft(90);
       dcr(step,0,length);
       turnright(45);
     end
     else
     begin
       turnright(45);
       forward(length);
       turnleft(90);
       forward(length);
       turnright(45);
     end;
   end
  else
   begin
     if step > 0 then
     begin
       turnleft(45);
       dcr(step,1,length);
       turnright(90);
       dcr(step,0,length);
       turnleft(45);
     end
     else
     begin
       turnleft(45);
       forward(length);
       turnright(90);
       forward(length);
       turnleft(45);
     end;
   end;
end;

main program:

begin
 init;
 penup;
 back(100);
 pendown;
 dcr(step,direction,length);
 close;
end.

This page uses content from Wikipedia. The original article was at Drachenkurve. The list of authors can be seen in the page history. As with Rosetta Code, the text of Wikipedia is available under the GNU FDL. (See links for details on variance)