include BDS.LIB
	include EPDATA

;jumped to when cseq finds draw command
;causes a break
;purpose is to skip up page and draw all lines
draw::
	push	b
;check there was no page break
	lhld	vposition
	xchg
	lhld	tm
	inx	h
	call	albu
	jc	.drX
;now save current v. position to return to when done drawing
	lhld	skdots
	dad	d
	push	h
;search lines to find how far back up the page we have to go
	lxi	h,lilist-6
	mvi	a,NUMLINES
	push	psw
	lxi	b,0FFFFH
.dr1:	pop	psw
	dcr	a
	jm	.dr3
	push	psw

	lxi	d,6
	dad	d
	mov	e,m
	inx	h
	mov	d,m
	inx	h
	mov	a,d
	ora	e
	jz	.dr1
	push	h
	mov	h,b
	mov	l,c
	call	albu
	jnc	$+5
	mov	b,d
	mov	c,e
	pop	h
	jmp	.dr1
.dr3:
;BC is min v. pos in list, or FFFF if none
	mov	d,b
	mov	e,c
	inx	d
	mov	a,d
	ora	e
	jz	.drRET
	dcx	d
	lhld	vposition
	call	cmh
	dad	d
;HL now neg. skips we have to do
	shld	skdots

;Ready to start drawing at v. position after next paperup
; (a) For each pass: clear buffer, draw 8 dots for each line, sendit
; (b) skip down for next row, and if not past old v. position, go to (a)
.drLOOP:
	call	drrow
	call	drrow
	call	drrow

	lhld	skdots
	lxi	d,PICA-3
	dad	d
	shld	skdots
	xchg
	lhld	vposition
	dad	d

;cf old v. position on stack
	pop	d
	push	d
	call	albu
	jnc	.drLOOP

.drRET:
;return down to v. position when got the draw command
	lhld	vposition
	call	cmh
	pop	d
	dad	d
	shld	skdots

;last thing to do is zero out the lines to show that they have been drawn
.drX:
	lxi	d,NUMLINES*8
	lxi	h,lilist
.drXL:	mvi	m,0
	inx	h
	dcx	d
	mov	a,d
	ora	e
	jnz	.drXL
	pop	b
	ret

;clear buffer, draw 8 dots for each line, sendit
drrow:
	call	clrgbuf##
	mvi	a,NUMLINES
	lxi	h,lilist
.drrLOOP:
	push	psw
	push	h
;no draw if no line
	mov	a,m
	inx	h
	ora	m
	dcx	h
	cnz	dr8
	lxi	d,8
	pop	h
	dad	d
	pop	psw
	dcr	a
	jnz	.drrLOOP
	call	bumpgpt##
	jmp	sendit##

;draw 8 dots for the line at HL
dr8:	lxi	d,v0
	mvi	b,8
.dr8.1:
	mov	a,m
	stax	d
	inx	h
	inx	d
	dcr	b
	jnz	.dr8.1

;y-coordinate
	lhld	vposition
	xchg
	lhld	skdots
	dad	d
;the first dot
	mvi	a,80H
.dr8LOOP:
	push	psw
	push	h
	call	dr1
	pop	h
	inx	h
	inx	h
	inx	h
	pop	psw
	ora	a
	rar
	jnc	.dr8LOOP
	ret

;draw one dot in Acc at y=HL
dr1:	mov	c,a	;to be passed to vdotset
	xchg
;DE = y
	lhld	v1
	call	albu	;passed where line starts?
	rnc
	lhld	v0
	call	cmh
	dad	d
	mov	a,h	;not yet to where line starts?
	ora	a
	rm

;no preadjust yet
	xra	a
	sta	_preadj
	call	adjfact

;v - v0
	push	h

	lhld	c1draw
	xchg
	lhld	c0draw
	push	h

	call	albu
	mvi	a,0
	jnc	$+5
	xchg
	inr	a

	sta	_nslflag

;HL is min(c0,c1)

	call	cmh
	dad	d
;save to figure num of dots
	shld	_hdiff
	call	adjfact
;HL is |c1 - c0|
	xchg
	pop	h
	xthl
;HL is v - v0 and c0 put back on stack
	call	usmul	
;HL is |c1 - c0|*(v - v0)
	push	h

	lhld	v1
	xchg
	lhld	v0
	call	cmh
	dad	d
;HL is v1 - v0

;pause to figure delta-h
	push	h
	xchg
	lhld	_hdiff
	xchg
	call	usdiv
	shld	_hdiff
	pop	d

	pop	h
;add den.-1 to numerator
	dcx	d

;(check not div by 0)
	mov	a,d
	ora	a
	jp	$+5
	pop	d	;clean stack and abort
	ret

	dad	d
	inx	d
;HL/DE
	xchg	
	call	usdiv
;HL is ( |c1 - c0|*(v - v0) )/(v1 - v0)

;adjust by lost factor
	lda	_preadj
	mov	e,a
	call	shllbe

	lda	_nslflag
	ora	a
	jz	$+6
	call	cmh

	pop	d	;(now stack clean)
	dad	d
;add min(c0,c1)

;(check bounds; OR in byte; set maxgpt up if less)
	xchg
	lda	_hdiff
	jmp	vvdotset##


adjfact:
	mov	a,h
	ora	a
	rz
	push	h
	lxi	h,_preadj
	inr	m
	pop	h
	inx	h	;?
	mvi	e,1
	call	shlrbe
	jmp	adjfact



v0:	dw	0
c0draw:	dw	0
v1:	dw	0
c1draw:	dw	0

_nslflag:	db	0
_preadj:	db	0
_hdiff:		dw	0

	end