Dragon curve: Difference between revisions

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The string rewrites can be done recursively without building the whole string, just follow its instructions at the target level. See for example [[#C by IFS Drawing|C by IFS Drawing]] code. The effect is the same as "recursive with parameter" above but can draw other curves defined by L-systems. <br><br>
The string rewrites can be done recursively without building the whole string, just follow its instructions at the target level. See for example [[#C by IFS Drawing|C by IFS Drawing]] code. The effect is the same as "recursive with parameter" above but can draw other curves defined by L-systems. <br><br>

=={{header|Ada}}==
This example uses GTKAda and Cairo.

<div>[[File:Dragoncurve ada cairo.png|thumb]]</div>

<syntaxhighlight lang="Ada">
-- FILE: dragon_curve.gpr --
with "gtkada";

project Dragon_Curve is
Adaflags := External_As_List ("ADAFLAGS", " ");
Ldflags := External_As_List ("LDFLAGS", " ");

for Languages use ("Ada");
for Main use ("dragon_curve.adb");
for Source_Dirs use ("./");
for Object_Dir use "obj/";
for Exec_Dir use ".";

package Compiler is
-- subprogram specs not required in testgtk
for Switches ("Ada") use ("-g", "-O0", "-gnaty-s", "-gnatwJ")
& Adaflags;
end Compiler;

-- package Linker renames Shared.Linker;
package Linker is
for Leading_Switches ("Ada") use Ldflags;
end Linker;

end Dragon_Curve;
</syntaxhighlight>

<syntaxhighlight lang="Ada">
-- FILE: dragon_curve.adb --
with Ada.Text_IO; use Ada.Text_IO;
with Events; use Events;
with GLib.Main; use GLib.Main;
with GTK;
with GTK.Drawing_Area; use GTK.Drawing_Area;
with GTK.Main;
with GTK.Window; use GTK.Window;

procedure Dragon_Curve is
Window : GTK_Window;
ID : GLib.Main.G_Source_ID;
begin
GTK.Main.Init;
GTK_New (Window);
GTK_New (Drawing_Area);
Window.Add (Drawing_Area);
Drawing_Area.On_Draw (Events.Draw'Access, Drawing_Area);
Show_All (Window);
Resize (Window, 800, 800);
GTK.Main.Main;
end Dragon_Curve;
</syntaxhighlight>

<syntaxhighlight lang="Ada">
-- FILE: events.ads --
with Ada.Numerics.Generic_Elementary_Functions;
with Cairo;
with GLib; use Glib;
with GTK.Drawing_Area; use GTK.Drawing_Area;
with GTK.Widget; use GTK.Widget;
with GLib.Object; use GLib.Object;

package Events is
Drawing_Area : GTK_Drawing_Area;

package GDouble_Elementary_Functions is new Ada.Numerics.Generic_Elementary_Functions (Float);
use GDouble_Elementary_Functions;

function Draw (Self : access GObject_Record'Class;
CC : Cairo.Cairo_Context)
return Boolean;
end Events;
</syntaxhighlight>

<syntaxhighlight lang="Ada">
-- FILE: events.adb --
with Cairo;
with GTK;

package body Events is
function Draw (Self : access GObject_Record'Class;
CC : Cairo.Cairo_Context)
return Boolean
is
type Rotate_Type is (Counterclockwise, Clockwise);

type Point is record
X, Y : GDouble;
end record;
procedure Heighway_Branch (CC : Cairo.Cairo_Context;
A, B : Point;
Rotate : Rotate_Type;
N : Natural)
is
R, RU, C : Point;
begin
if N = 0 then
Cairo.Move_To (CC, A.X, A.Y);
Cairo.Line_To (CC, B.X, B.Y);
Cairo.Stroke (CC);
else
-- Rotate 45 degrees --
case Rotate is
when Clockwise =>
R.X := GDouble ((1.0 / Sqrt (2.0)) * Float (B.X - A.X)
- (1.0 / Sqrt (2.0)) * Float (B.Y - A.Y));
R.Y := GDouble ((1.0 / Sqrt (2.0)) * Float (B.X - A.X)
+ (1.0 / Sqrt (2.0)) * Float (B.Y - A.Y));
when Counterclockwise =>
R.X := GDouble ((1.0 / Sqrt (2.0)) * Float (B.X - A.X)
+ (1.0 / Sqrt (2.0)) * Float (B.Y - A.Y));
R.Y := GDouble (-(1.0 / Sqrt (2.0)) * Float (B.X - A.X)
+ (1.0 / Sqrt (2.0)) * Float (B.Y - A.Y));
end case;

-- Make unit vector from rotation --
RU.X := GDouble (Float (R.X) / Sqrt ( Float (R.X ** 2 + R.Y ** 2)));
RU.Y := GDouble (Float (R.Y) / Sqrt ( Float (R.X ** 2 + R.Y ** 2)));

-- Scale by half the length of A->B --
R.X := RU.X * GDouble (Sqrt (Float (B.X - A.X) ** 2 + Float (B.Y - A.Y) ** 2) / Sqrt (2.0));
R.Y := RU.Y * GDouble (Sqrt (Float (B.X - A.X) ** 2 + Float (B.Y - A.Y) ** 2) / Sqrt (2.0));

C := (R.X + A.X, R.Y + A.Y);
Heighway_Branch (CC, A, C, Clockwise, N - 1);
Heighway_Branch (CC, C, B, Counterclockwise, N - 1);
end if;
end Heighway_Branch;

Depth : constant := 14;
Center, Right, Bottom, Left: Point;
Width : GDouble := GDouble (Drawing_Area.Get_Allocated_Width);
Height : GDouble := GDouble (Drawing_Area.Get_Allocated_Height);

begin
Center := (Width / 2.0, Height / 2.0);
Right := (Width, Height / 2.0);
Left := (0.0, Height / 2.0);
Bottom := (Width / 2.0, Height);

Cairo.Set_Source_RGB (CC, 0.0, 1.0, 0.0);
Heighway_Branch (CC, Center, Right, Clockwise, Depth);
Cairo.Set_Source_RGB (CC, 0.0, 1.0, 1.0);
Heighway_Branch (CC, Center, Left, Clockwise, Depth);
Cairo.Set_Source_RGB (CC, 0.0, 1.0, 0.5);
Heighway_Branch (CC, Center, Bottom, Clockwise, Depth);
return True;
end Draw;
end Events;
</syntaxhighlight>


=={{header|Action!}}==
=={{header|Action!}}==
Retrieved from "https://rosettacode.org/wiki/Dragon_curve"