uses GraphABC;

procedure RLine(x, y, x1, y1: real) := Line(Round(x), Round(y), Round(x1), Round(y1));

function GetAngle(x, y, x2, y2: real): real;
begin
  var angle := Abs(RadToDeg(ArcTan((y2 - y) / (x2 - x))));
  if (x2 = x) and (y2 = y) then
    Result := 0
  else
    if x2 > x then
      if y2 > y then Result := angle else Result := 360 - angle
    else
      if y2 > y then Result := 180 - angle else Result := 180 + angle;
end;

function Distance(x, y, x1, y1: real) := Sqrt(Sqr(x1 - x) + Sqr(y1 - y)); 

procedure Draw(x, y, x1, y1: real);
begin
  if Distance(x, y, x1, y1) > 1 then
  begin
    var dx := (x1 - x) / 3;
    var dy := (y1 - y) / 3;
    
    var x2 := x + dx;
    var y2 := y + dy;
    
    var angle := DegToRad(GetAngle(x, y, x1, y1) - 60);
    var r := Distance(x, y, x2, y2);
    
    var x3 := x2 + r * Cos(angle);
    var y3 := y2 + r * Sin(angle);
    
    var x4 := x + dx * 2;
    var y4 := y + dy * 2;
    
    Draw(x, y, x2, y2);
    Draw(x2, y2, x3, y3);
    Draw(x3, y3, x4, y4);
    Draw(x4, y4, x1, y1);
  end
  else
    RLine(x, y, x1, y1);
end;

begin
  SetWindowSize(500, 500);
  SetWindowIsFixedSize(true);
  ClearWindow(clBlack);
  LockDrawing();
  
  SetPenColor(clCyan);
  Draw(100, 100, 400, 100);
  Draw(400, 100, 400, 400);
  Draw(400, 400, 100, 400);
  Draw(100, 400, 100, 100);
  Redraw();
end.