REM Dragon curve
REM SIN, COS in arrays for PI/4 multipl.
DECLARE SUB Dragon (BYVAL Insize!, BYVAL Level%, BYVAL RQ%)
DIM SHARED S(7), C(7), X, Y, RotQPi%
CONST QPI = .785398163397448# ' PI / 4
FOR I = 0 TO 7
  S(I) = SIN(I * QPI)
  C(I) = COS(I * QPI)
NEXT I
X = 112: Y = 70
SCREEN 2: CLS
CALL Dragon(128, 15, 1) ' Insize = 2^WHOLE_NUM (looks better)
END

SUB Dragon (BYVAL Insize, BYVAL Level%, BYVAL RQ%)
  CONST SQ = 1.4142135623731# ' SQR(2)
  IF Level% <= 1 THEN
    XN = C(RotQPi%) * Insize + X
    YN = S(RotQPi%) * Insize + Y
    LINE (2 * X, Y)-(2 * XN, YN) ' For SCREEN 2 doubled x-coords
    X = XN: Y = YN
  ELSE
    RotQPi% = (RotQPi% + RQ%) AND 7
    CALL Dragon(Insize / SQ, Level% - 1, 1)
    RotQPi% = (RotQPi% - RQ% * 2) AND 7
    CALL Dragon(Insize / SQ, Level% - 1, -1)
    RotQPi% = (RotQPi% + RQ%) AND 7
  END IF
END SUB