[atari7800] Re: Please help me understand display lists and display list lists

Hi Dennis,

I'm not an Atari 800 guy, but I can explain this best the way that I
learned it.

I found this easiest to understand the 7800's drawing mechanisms by using
the "Frogger" model.  I started to whip up a Frogger-like demo about 2 and
a half years ago, and when it got closer to being playable (instead of just
some random graphics floating around), I hit a couple of snags.  But, those
are irrelevant to the topic at hand.

Ok, in the street in Frogger, you've got cars.  Each "header" contains
information about one single car sprite.  Take a bunch of these together in
a horizontal area (or "zone"), and you've essentially got a list of
headers.  In an organized format (represented as a header after another
header, etc... until some termination bytes), these make up a "display
list".  But, since you've got multiple "zones" where cars can be, you need
to keep a list that tells where each Display list's starting address is in
order from top-to-bottom of the screen, and how many vertical pixels down
each zone goes.  This information makes up your Display List List (or DLL).

That's probably too quick-and-dirty-- Is this sort of what you're looking
for?  If so, I may be able to dig up some code samples.

Regards,
-John K. Harvey


At 10:16 PM 11/19/03 -0500, you wrote:
>Hi all,
>
>From my understanding the 7800 processes graphics on a line by line bases.
>So you're only limited in the amount of sprites per line by how long it
>takes you to draw them. I've done this (sort of) on the A8 with different
>ANTIC modes (such as ANTIC E and ANTIC F) but it's still going to take some
>getting use to. I've also dealt with display lists in the A8 for so long
>that I still can't get a grasp on to the 7800 concept. Anyone know of a way
>that would help me understand it better? A number of you come from the A8
>environment. Did any of you have trouble getting this? If so, how did you
>overcome it?
>
>
>Take care,
>Dennis
>
>
>
>
>
>

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