Path: utzoo!utgpu!cs.utexas.edu!swrinde!mips!spool.mu.edu!munnari.oz.au!bruce!goanna!minyos.xx.rmit.oz.au!s902113
From: s902113@minyos.xx.rmit.oz.au (Luke Mewburn)
Newsgroups: alt.sources.amiga
Subject: Re: Starting to code Demos
Message-ID: <1991Jun24.225534.8494@minyos.xx.rmit.oz.au>
Date: 24 Jun 91 22:55:34 GMT
References: <9106221057.AA02538@ucbvax.Berkeley.EDU> <1991Jun23.004739.25215@marlin.jcu.edu.au> <1991Jun24.055126.20856@minyos.xx.rmit.oz.au> <1991Jun24.090126.21934@marlin.jcu.edu.au> <1991Jun24.152441.24809@hollie.rdg.dec.com>
Organization: RMIT Computer Centre, Melbourne Australia.
Lines: 37

jamie@sievax.enet.dec.com (Jamie Badman) writes:

[... arguments for/against using assembler direct to hardware ...]

>It's very obvious that you've never done much with your machine in terms
>of trying to code up demos. As someone mentioned earlier, it's not just
>the speed that you need to achieve with the code, it's a question of
>counting CPU cycles in order to perform various effects and
>synchronisations. I know this is an Amiga group but most of my coding
>experience is on the Atari ST (I recently swapped for an Amiga for a
>change). On the ST there is an effect called hardware or DMA scrolling.
>This is VERY fast full screen scrolling that has only been used on the
>machine in the last 18 months or so. To achieve this scrolling effect
>you need to be spot on with your CPU cycles; you screw that up and your
>scroll doesn't work. Full Stop. Try doing that in C and let us all have
>a good belly laugh!!!

The technique of counting cycles, etc, to speed up graphics and get
wonderful effects has been used for years on machines like the C64,
Spectrum, Amstrad, etc. _IT WORKS_, very well in fact. The reason why
people use it is so they can push their hardware to the max. The
disadvantages of this are known: ie, don't work on machines with different
hardware or faster clocks (ie, A3000's, et al), or on machines which use
the refresh rate as a counter, so the other screen display types (NTSC or
PAL - depending on where you are) breaks.
  The poster who slagged off about using this technique might have had a
point: in applications (or even games); but demos are there to show off
mainly:
  - programmer's skill (look at the demos last year which tried to outdo
	each other in 3-d rotating graphics :-)
  - computer's ability in graphics/sound.  (Most of the better music on
	the amiga comes from demos, not games or composed stuff...)


>				Jamie.

Luke...