XLIB	invpixel

	LIB pixeladdress
	XREF	COORDS

; ******************************************************************
;
; Inverse	pixel at (x,y)	coordinate
;
; Design & programming by Gunther Strube, Copyright (C) InterLogic 1995
;
; in:  hl	= (x,y) coordinate of pixel (h,l)
;
; registers changed	after return:
;  ..bc..../ixiy same
;  af..dehl/.... different
;
.invpixel			ld	a,l
				cp	64
				ret	nc				; y0	out of range...

				push	bc
				ld	(COORDS),hl		; save new plot coordinate
				ld	a,l
				xor	@00111111			; (0,0) is hardware	(0,63)
				ld	l,a
				call	pixeladdress
				ld	b,a
				ld	a,1
				jr	z, xor_pixel
.inv_position		rlca
				djnz	inv_position
.xor_pixel		ex	de,hl
				xor	(hl)
				ld	(hl),a
				pop	bc
				ret