p_VLine:
	.db __VLineEnd-$-1
	ld	de,plotSScreen
x_VLineEntry:

;; de=buff, l=y2, (sp)=ret, (sp+2)=y1, (sp+4)=x
;; Rearrange stuff
	ld	a,l
	pop	hl
	pop	bc
	ex	(sp),hl

;; a=y2, c=y1, de=buff, l=x
;; Check if y1 is offscreen top while calculating y1*2; if so, note and fix it
	ld	h,0
	sla	c
	jr	nc,$+3
	ld	c,h

;; carry=y1 offscreen, a=y2, c=top-fixed y1*2, de=buff, h=0, l=x
;; Check if y2 is offscreen top while calculating y2*2; if so, abort if y1 was
;;   too, then fix it
	rla
	jr	nc,$+5
	rra
	ret	c
	ld	a,h

;; a=top-fixed y2*2, c=top-fixed y1*2, de=buff, h=0, l=x
;; Check that y2>=y1; if not, swap y1 and y2
	cp	c
	jr	nc,$+5
	ld	b,c
	ld	c,a
	ld	a,b

;; y1 is now guaranteed to be <=y2
;; a=top-fixed y2*2, c=top-fixed y1*2, de=buff, h=0, l=x
;; Check if y1 is offscreen bottom while calculating y1*4; if so, abort
	sla	c
	ret	c

;; a=top-fixed y2*2, c=fixed y1*4, de=buff, h=0, l=x
;; Check if y2 is offscreen bottom while calculating y2*4; if so, fix it
	add	a,a
	jr	nc,$+4
	ld	a,63

;; Y Clipping complete; y1 and y2 guaranteed to be onscreen
;; a=y2*4, c=y1*4, de=buff, h=0, l=x
;; Calculate the height of the line
	sub	c
	rra
	rra
	inc	a
	ld	b,a

;; y2 no longer needed
;; a=height, b=height, c=y1*4, de=buff, h=0, l=x
;; Calculate x1/8 and add it and y*12 to the buffer pointer
	ex	de,hl
	ld	a,e
	ld	e,c
	ld	c,a
	add	hl,de
	rra
	add	hl,de
	rra
	add	hl,de
	rra
	ld	e,a
	add	hl,de


;; y1 no longer needed
;; a=x/8, b=height, c=x, d=0, e=x/8, hl=y1*12+(x/8)+buff
;; Check if x is offscreen; if so, abort
	ld	e,12
	cp	e
	ret	nc

;; Begin drawing!
;; a=x/8, b=height, c=x, de=12, hl=y1*12+(x/8)+buff
;; Calculate the mask
	ld	a,c
	or	%11111000
	ld	c,d
	scf
__VLineMaskLoop:
	rl	c
	inc	a
	jr	nz,__VLineMaskLoop


;; a=0, b=height, c=mask, de=12, hl=y1*12+(x/8)+buff
;; Draw the line
__VLineLoop:
	ld	a,(hl)
	or	c
	ld	(hl),a
	add	hl,de
	djnz	__VLineLoop

	ret
__VLineEnd: