Nick S Bensema wrote:
>
> > 1- learn the basic concepts from the programmer's guide. And I mean
> > "basic": don't waste time on VDEL, for example! What's the use of VDEL,
> > anyway? ;-)
>
> It's my understanding that when VDEL is enabled, a player's graphics don't
> change immediately when its data register changes; it waits until the
> next write to player data before it makes the change. This was intended
> to allow single-scanline positioning in double-scanline kernels, but
> its most common use is in six-digit scoring routines.
>
> I once thought, maytbe it would be a good idea to study Rob Colbert's notes
> and produce a text file explaining it, but then I figured, this type of
> code is usually just copied straight from disassembled listings anyway.
> Perhaps I (or someone who can beat me to it) should write a tutorial on
> stealing code from 2600 games, starting with six-digit scores.
I use it in TPS for updating GRP1 (the asteroids and enemy craft) late
in the scanline, and indeed it does just what you say. It seems there
are a great many kernel variations possible if you don't need to worry
about when your updates are done during the scanline, but delay them
until the WSYNC. I think you could produce some really significant
single scanline stuff with VDEL on all the time for both sprites. The
6-digit score is just one of the most common hacks to use it.
--
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