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From: spence@cbmvax.commodore.com (Spencer Shanson)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: 3D stuff & quick line drawing
Message-ID: <20967@cbmvax.commodore.com>
Date: 26 Apr 91 14:49:12 GMT
Article-I.D.: cbmvax.20967
References: <1991Apr21.081925.4722@lynx.CS.ORST.EDU> <1991Apr22.122442.25505@cs.umu.se> <20884@cbmvax.commodore.com> <1991Apr24.203219.22776@cs.umu.se>
Reply-To: spence@cbmvax.commodore.com (Spencer Shanson)
Organization: Commodore, West Chester, PA
Lines: 63



In article <1991Apr24.203219.22776@cs.umu.se> dvljrt@cs.umu.se (Joakim Rosqvist) writes:
>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]
>>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.
>>
>>** You need to WaitBlit() here
>
>Sorry, I though Ownblitter meant 
>'when you have called this function, you own the blitter'
>

You do own the blitter, but that does not mean that the last blit has finished
yet. This will be especially true on a faster CPU and a large blit. Even your
own code does its final blit and then disowns it.

>>** 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.
>

That's up to you, just don't expect the code to run on every Amiga. At the
very least, take into account the hardware bugs described in the
autodocs.

>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.
>

You don't say if the lines are arbitrary direction. Sure, for short horizontal
lines, you would be better off using the CPU, but I doubt that's the case for
lines of any angle of more than a few pixels.

>/$DR.HEX$
-- 
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Spencer Shanson - Amiga Software Engineer     | email: spence@commodore.COM
                                              | or uunet!cbmvax!spence
All opinions expressed are my own, and do not | "You know my methods. Apply
(necessarily) represent those of Commodore.   | them" -- Sir Arthur Conan
                                              | Doyle - 'The Sign of Four'