Subj : Re: Summer Games
To   : Andreas Kohlbach
From : Tom Lake
Date : Sun Jun 09 2019 03:18 pm

On Sunday, June 9, 2019 at 5:03:27 PM UTC-4, Andreas Kohlbach wrote:
> On Sat, 08 Jun 2019 20:32:30 +1300, Frank Linhares wrote:
> >
> >  TL> As long as the doves stay in the sky and the fire stays OUT of the sky
> >  TL> and away from the ground, they might have used vertical interrupts to
> >  TL> switch sprite sets as the electron beam hit certain parts of the 
screen.
> >  TL> Think of it like a layer cake. Each
> >  TL> layer can have up to eight sprites which are independent of the 
sprites
> >  TL> in any other layer. On the 64, the layers can be different widths. You
> >  TL> can have dozens of sprites on the screen at the same time but each 
group
> >  TL> of eight can only stay in its own
> >  TL> layer.
> >
> > Many of the demo scene demos from back in the day (and currently) took
> > advantage of vertical interrupts to make incredible demos. I would bet that
> > Epyx did the same.
>
> Thank you and Tom. So vertical interrupts might made this
> happen. Amazing, because in 1984 the Commodore 64 was only two years old.
> --
> Andreas
>
> My random thoughts and comments
> https://news-commentaries.blogspot.com/

The technique was documented in the Commodore 64 Programmer's Reference manual 
which was available at the beginning of January 1983 so it wasn't one of those 
hidden features that had to be discovered by users.

Tom L

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