xlib	turn

	xref	HEADING

if QDOS
	include "#fpp_def"
else
	if z88
		include ":*//fpp.def"
	else
		include "#fpp.def"
	endif
endif


; ****************************************************************************
;
; Move turtle heading in	relative degrees (+/-)
;
; Design & programming by Gunther Strube, Copyright (C) InterLogic 1995
;
; IN:	HL =	relative heading in	degrees (+/-)
; OUT:	None.
;
;	Registers	affected after	return:
;		AFBCDEHL/IXIY	same
;		......../....	different
;
.turn			push	af
				push	bc
				push	de
				push	hl

				ld	de,360
				ld	bc,(HEADING)		; calculate relative heading direction
				add	hl,bc
				exx
				ld	bc,0
				ld	hl,0
				ld	de,0
				fpp(FP_MOD)			; heading	modulus 360
				exx
				ld	(HEADING),hl		; new heading in absolute degrees...

				pop	hl
				pop	de
				pop	bc
				pop	af
				ret