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

dan, can you post the vertcal sprite movement example on your site???

or was it eckard posting somewhere @ atariage?

cheers, hve

ps. a7800 is a raw but nice beast
pss. building DLL structure is the key... otherwise how would you manage to 
have a variable sprite amount per scanline???

>From: "Dan Boris" <dboris@xxxxxxxxxxx>
>Reply-To: atari7800@xxxxxxxxxxxxx
>To: <atari7800@xxxxxxxxxxxxx>
>Subject: [atari7800] Re: Please help me understand display lists and  
>display list lists
>Date: Thu, 20 Nov 2003 16:52:27 -0500
>
>This is a good description, but the part of this I had a hard time
>getting my mind around was how a sprite moved from one zone to another.
>To make this happen you need to make a DL entry for the sprite in each
>zone. You then have to change the pointer to the graphics data so that
>in the top zone the sprite shifts down and gets cut off on the bottom,
>and in the bottom zone the top of the sprite gets cut off. Once you
>understand the need for Holey DMA will suddently become clear.
>
>The other revelation that really helped me understand the 7800 hardware
>was that you really shouldn't attempt to go directly from game logic, to
>DL data structures. You should build a "display engine" the goes in
>between. Take Robotron for example. I disassembled some of this game to
>get an idea how it worked. They define a sprite table in RAM that
>contains such information as the X,Y position of the sprite, which
>sprite "character" to display, which frame of animation to use, etc. The
>game logic writes to this table, then the display engine processes this
>table and turns it into the DL structures needed to generate the
>display.
>
>Dan
>
>
>-----Original Message-----
>From: atari7800-bounce@xxxxxxxxxxxxx
>[mailto:atari7800-bounce@xxxxxxxxxxxxx] On Behalf Of John K. Harvey
>Sent: Thursday, November 20, 2003 12:15 AM
>To: atari7800@xxxxxxxxxxxxx
>Subject: [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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