gistfile1.pas

procedure TForm1.DrawCircle3(cx, cy, r: Integer);
var
  angle, angleInc : Extended;
  i : integer;
  x, y, sina, sinb, cosa, cosb, sinab, cosab : Extended;
begin
  PaintBox1.Canvas.MoveTo(cx + r, cy);

  angleinc := 360 / r;
  sinb := Sin(angleinc / (180.0 / 3.14159));
  cosb := Cos(angleinc / (180.0 / 3.14159));

  sina := 0;
  cosa := 1;

  i := Round(360 / angleinc);
  while i > 0 do
  begin
    sinab := sina * cosb + cosa * sinb;
    cosab := cosa * cosb - sina * sinb;
    x := r * cosab;
    y := r * sinab;
    sina := sinab;
    cosa := cosab;
    Dec(i);
    PaintBox1.Canvas.LineTo(Round(x) + cx, Round(y) + cy);
  end;
end;