Task: Sierpinski arrowhead curve




Go: package main

import (
    "github.com/fogleman/gg"
    "math"
)

var (
    width  = 770.0
    height = 770.0
    dc     = gg.NewContext(int(width), int(height))
    iy     = 1.0
    theta  = 0
)

var cx, cy, h float64

func arrowhead(order int, length float64) {
    
    if order&1 == 0 {
        curve(order, length, 60)
    } else {
        turn(60)
        curve(order, length, -60)
    }
    drawLine(length) 
}

func drawLine(length float64) {
    dc.LineTo(cx-width/2+h, (height-cy)*iy+2*h)
    rads := gg.Radians(float64(theta))
    cx += length * math.Cos(rads)
    cy += length * math.Sin(rads)
}

func turn(angle int) {
    theta = (theta + angle) % 360
}

func curve(order int, length float64, angle int) {
    if order == 0 {
        drawLine(length)
    } else {
        curve(order-1, length/2, -angle)
        turn(angle)
        curve(order-1, length/2, angle)
        turn(angle)
        curve(order-1, length/2, -angle)
    }
}

func main() {
    dc.SetRGB(0, 0, 0) 
    dc.Clear()
    order := 6
    if order&1 == 0 {
        iy = -1 
    }
    cx, cy = width/2, height
    h = cx / 2
    arrowhead(order, cx)
    dc.SetRGB255(255, 0, 255) 
    dc.SetLineWidth(2)
    dc.Stroke()
    dc.SavePNG("sierpinski_arrowhead_curve.png")
}








Ada: with Ada.Command_Line;
with Ada.Numerics.Generic_Elementary_Functions;
with Ada.Text_IO;
with PDF_Out;

procedure Arrowhead_Curve is

   package Real_Math is
     new Ada.Numerics.Generic_Elementary_Functions (PDF_Out.Real);
   use Real_Math, PDF_Out, Ada.Command_Line, Ada.Text_IO;

   subtype Angle_Deg  is Real;
   type    Order_Type is range 0 .. 7;

   Purple : constant Color_Type := (0.7, 0.0, 0.5);
   Length : constant Real       := 340.0;
   Corner : constant Point      := (120.0, 480.0);

   Order     : Order_Type;
   Current   : Point      := (0.0, 0.0);
   Direction : Angle_Deg  := Angle_Deg'(0.0);
   Doc       : PDF_Out_File;

   procedure Curve (Order : Order_Type; Length : Real; Angle : Angle_Deg) is
   begin
      if Order = 0 then
         Current := Current + Length * Point'(Cos (Direction, 360.0),
                                              Sin (Direction, 360.0));
         Doc.Line (Corner + Current);
      else
         Curve (Order - 1, Length / 2.0, -Angle);  Direction := Direction + Angle;
         Curve (Order - 1, Length / 2.0,  Angle);  Direction := Direction + Angle;
         Curve (Order - 1, Length / 2.0, -Angle);
      end if;
   end Curve;

begin
   if Argument_Count /= 1 then
      Put_Line ("arrowhead_curve <order>");
      Put_Line ("  <order>   0 .. 7");
      Put_Line ("open sierpinski-arrowhead-curve.pdf to view ouput");
      return;
   end if;
   Order := Order_Type'Value (Argument (1));

   Doc.Create ("sierpinski-arrowhead-curve.pdf");
   Doc.Page_Setup (A4_Portrait);
   Doc.Margins (Margins_Type'(Left   => Cm_2_5,
                              others => One_cm));
   Doc.Stroking_Color (Purple);
   Doc.Line_Width (2.0);
   Doc.Move (Corner);
   if Order mod 2 = 0 then
      Direction := 0.0;
      Curve (Order, Length, 60.0);
   else
      Direction := 60.0;
      Curve (Order, Length, -60.0);
   end if;
   Doc.Finish_Path (Close_Path => False,
                    Rendering  => Stroke,
                    Rule       => Nonzero_Winding_Number);
   Doc.Close;
end Arrowhead_Curve;