Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!uupsi!sunic!cs.umu.se!dvljrt
From: dvljrt@cs.umu.se (Joakim Rosqvist)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: 3D stuff & quick line drawing
Message-ID: <1991Apr24.203219.22776@cs.umu.se>
Date: 24 Apr 91 20:32:19 GMT
References: <1991Apr21.081925.4722@lynx.CS.ORST.EDU> <1991Apr22.122442.25505@cs.umu.se> <20884@cbmvax.commodore.com>
Sender: news@cs.umu.se (News Administrator)
Organization: Dep. of Info.Proc, Umea Univ., Sweden
Lines: 53

In article <20884@cbmvax.commodore.com> spence@cbmvax.commodore.com (Spencer Shanson) writes:
>
>
>In article <1991Apr22.122442.25505@cs.umu.se> dvljrt@cs.umu.se (Joakim Rosqvist) writes:
>> [stuff deleted]
>>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)
>
>Great! But you also need to WaitBlit() after owning the blitter (just to be 
>safe), and just before starting to write to any of the blitter registers.
>
>>[stuff deleted]
>>	jsr	OwnBlitter(a6)
>>	
>>	lea	$dff000,a6
>
>** You need to WaitBlit() here

Sorry, I though Ownblitter meant 
'when you have called this function, you own the blitter'

>
>>	move	#$8000,BLTADAT(a6)
>> [more stuff deleted]
>>wait:	btst	#6,DMACONR(a6)
>>	bne.s	wait
>
>** Better to use WaitBlit(), which knows about various Agnus hardware bugs
>** (see Autodocs for more details)

The issue here was fast lines, if I could consider calling a ROM-routine
I could just as well have called 'drawline' (or sth, I've never used it)
in gfxlib in the first place.

BTW, i read in another article that using the blitter on short lines
should be a disadvantage because of the long setup-time. The breakoff
was given to about 150 pixels. I don't know what processor was intended
but I made a little test in the following environment:

Program ran from fastmem, 68000 used, 1 bitplane 640x256 shown and
no interrupts enabled.
With the blitter i got 738000 pixels/second and 23 microsecond startup-time
which equals 17 extra pixels on every line. Lines between 1..25 pixels
all take the same time. The is beacuse the setup-time was really 58 micros
but for longer lines some of this could be done while the blitter was
drawing the previous line.
With the 68000 i could get about 150000 pixels/sec and 24 micros 'setup'
(I clocked a MAC SE/30 using quickdraw to 110000 pix/sec  giggle..)
This means that the breakoff(=the number of pixels where using the blitter
or the 68000 would take the same time) would be at 5 pixels.

/$DR.HEX$