Here is a part of the source i use when i want *fast* lines.
It uses the blitter and writes directly to the DFF regs
(no flames please, i *did* call Ownblitter first)
There are som things left out, like where how to find the address of the 
bitplane to draw in, and where the coordinates comes from, but that
should be easy to fill in.
/$DR.HEX$


DMACONR=2
BLTCON0=$40
BLTCON1=$42
BLTAMOD=$64
BLTBMOD=$62
BLTCMOD=$60
BLTAPT=$50
BLTCPT=$48
BLTDPT=$54
BLTADAT=$74
BLTBDAT=$72
BLTAFWM=$44
BLTSIZE=$58

OwnBlitter=-456
DisownBlitter=-462

width=80	;80 bytes = 640 pixels



Draw_all_lines:
	move.l	4.w,a6
	move.l	(a6),a6
	move.l	(a6),a6	;get base of Gfxlib
	jsr	OwnBlitter(a6)
	
	lea	$dff000,a6
	move	#$8000,BLTADAT(a6)
	move	#-1,BLTAFWM(a6)
	move	#width,BLTCMOD(a6)
	move	#$FFFF,BLTBDAT(a6)	;$FFFF=draw , $0000=clear
;These values are the same for all lines, no need to tell
;the blitter about them more than once
	
	move.l	<startaddress of bitplane>,a0
	moveq	#<numlines-1>,d7
	bsr.s	drawem
	move.l	4.w,a6
	move.l	(a6),a6
	move.l	(a6),a6
	jmp	DisOwnBlitter(a6)
	

drawem:	move	<X0>,d0
	move	<Y0>,d1
	move	<X1>,d2
	move	<Y1>,d3
	
	moveq	#width,d4
	mulu	d1,d4
;This could be sped up by reading a table with values
;0,width,width*2,width*3 etc.
	moveq	#-16,d5
	and	d0,d5
	lsr	#3,d5
	add	d5,d4
	add.l	a0,d4
	moveq	#0,d5
	sub	d1,d3
	roxl.b	#1,d5
	tst	d3
	bge.s	y2gy1
	neg	d3
y2gy1:	sub	d0,d2
	roxl.b	#1,d5
	tst	d2
	bge.s	x2gx1
	neg	d2
x2gx1:	move	d3,d1
	sub	d2,d1
	bge.s	dygdx
	exg	d2,d3
dygdx:	roxl.b	#1,d5
	move.b	table(pc,d5.w),d5
	add	d2,d2
wait:	btst	#6,DMACONR(a6)
	bne.s	wait
	move	d2,BLTBMOD(a6)
	sub	d3,d2
	bge.s	signn1
	or.b	#$40,d5
signn1:	move	d2,BLTAPT+2(a6)
	sub	d3,d2
	move	d2,BLTAMOD(a6)
	and	#15,d0					
	ror	#4,d0
	or	#$bca,d0
	move	d0,BLTCON0(a6)
	move	d5,BLTCON1(a6)
	move.l	d4,BLTCPT(a6)
	move.l	d4,BLTDPT(a6)
	addq	#1,d3
	lsl	#6,d3
	addq	#2,d3
	move	d3,BLTSIZE(a6)	;GO!
	dbra	d7,drawem	;do next line
	rts
	
table:	dc.b 1,17,9,21,5,25,13,29