// https://ru.wikibooks.org/wiki/Книга программиста/Книга фракталов
uses GraphABC;
const
  Min = 1;
  DeltaAng = Pi / 20;
  CX = 320;
  CY = 240;

var
  R: real;
  A: real;

procedure Draw(r, angle: real);
begin
  var ang1 := angle + Pi / 4;
  var x1 := Round(CX + r * Cos(ang1));
  var y1 := Round(CY + r * Sin(ang1));
  
  var ang2 := angle + 3 / 4 * Pi;
  var x2 := Round(CX + r * Cos(ang2));
  var y2 := Round(CY + r * Sin(ang2));
  
  var ang3 := angle + 5 / 4 * Pi;
  var x3 := Round(CX + r * Cos(ang3));
  var y3 := Round(CY + r * Sin(ang3));
  
  var ang4 := angle + 7 / 4 * Pi;
  var x4 := Round(CX + r * Cos(ang4));
  var y4 := Round(CY + r * Sin(ang4));
  
  Line(x1, y1, x2, y2);
  Line(x2, y2, x3, y3);
  Line(x3, y3, x4, y4);
  Line(x4, y4, x1, y1);
end;

begin
  R := 320;
  A := 0;
  
  LockDrawing();
  repeat
    Draw(R, A);
    A := A + DeltaAng;
    R := R * Sin(Pi / 4) / Sin(3 * Pi / 4 - DeltaAng);
  until R <= Min;
  Redraw();
end.