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Simple question about Frogs & Flies and Atari text


Aloan

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My simple 2 Atari 2600 questions are:

 

1- In Frogs & Flies, how is the river made? is it a continuation of the background? but isn't a backgorund only one color? can one change the color mid scan line?

2- How is text created in the Atari 2600? thanks

Edited by Aloan
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Stella has a really slick feature call Fixed Debug Colors, it's toggled by one of the Developer Keys. It turns this:

post-3056-0-26715700-1440722867_thumb.png

 

into this:

post-3056-0-93964100-1440722884_thumb.png

 

With a handy little chart it reveals that yep, the river is just the background with a different color. Likewise it reveals that the frogs are players (Atari's name for sprites) while the flies are missiles - missiles are basically a 1 pixel player that can be displayed with a width of 1x, 2x, 4x or 8x.

post-3056-0-85886400-1440722932_thumb.gif

 

There's a number of ways to generate text on the Atari - use Fixed Debug Colors to see how the programs you're wondering about do it.

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...I thought player0 if it were to be duplicated or triplicated, all parts would have to be clones! but for example, in the Cat trax game, that is not the case!

All copies would display identical. But the code manages to change the data between the copies' display. Exact timing is crucial here.

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All copies would display identical. But the code manages to change the data between the copies' display. Exact timing is crucial here.

hehe! it is wonderful how you devs pull it off! with a ONE player0 you create from top to bottom a score, then an actual player and even a part of a text below the screen - which would then be mixed with player1 with other parts of that text and so on!

Edited by Aloan
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Yep - with duplicate and triplicate you can update the graphics between each copy so they each show something different. It's the same concept as updating the playfield registers so the left and right sides of the screen are different, though the timing's much trickier for the players.

 

Minidig has a nice collection of info on programming the Atari, the tricks page has a bit on VDEL which is used to draw a "48 pixel sprites", which is the technique used in most later games to display a 6 digit score.

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Yep - with duplicate and triplicate you can update the graphics between each copy so they each show something different. It's the same concept as updating the playfield registers so the left and right sides of the screen are different, though the timing's much trickier for the players.

 

Minidig has a nice collection of info on programming the Atari, the tricks page has a bit on VDEL which is used to draw a "48 pixel sprites", which is the technique used in most later games to display a 6 digit score.

That's great! I'll check them both! :)

Edited by Aloan
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There's something odd with the link to your site. Looks like there's characters after it which the browser is converting to %C2%A0 so the link becomes:

http://aloan.site90.net/atari_graphics_simplified.html%C2%A0

which fails to work. If I take off the %C2%A0 the link works.

 

http://aloan.site90.net/atari_graphics_simplified.html

 

Site looks good, I especially like the colorful text on the black background - gives it an old school feel, which is appropriate for an old school topic.

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I understand that I took the whole screen for this, which is not correct as the display would only be half its width!? (the other half mirrored or repeated)

or can this actually be possible in the At2600?

 

Not sure if you realized this or not. It is possible to create an asymmetric playfield instead of repeating or mirroring the left half. It just requires a kernel that updates the PF registers twice each scan line. The drawback to doing this is that you don't have much time to update the rest of the graphics. A common compromise is to only update the PF1 and PF2 registers twice while leaving the left and right 4 PF pixels blank. This gets you a 32 pixel wide playfield with only 4 PF register writes instead of the 6 that are required for a full asymmetric playfield.

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Yep, as ZackAttack says you can update the playfield registers so the left and right sides show different images. Takes a lot of cycles per scanline though, plus you have to time it right (though there's quite a bit of flexibility for the timing). In Stay Frosty I mirrored the screen and only updated PF1 and PF2. In Stay Frosty 2 I used the time saved by utilizing DPC+ to also update PF0.

 

My blog series Collect, which documents how to develop a 2K assembly language game from scratch, shows how to do this in Step 3 - Score & Timer display. I only needed to update PF1 to show the score and timer, but the concept is the same for PF0 and PF2.

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Well, today I went and created a program from scratch that can do what I am saying...

txt instructions are in the download as well!

The ability to do the background will have to wait, but meanwhile, black background will do!

I will be working on bringing mirrored, repeated and asymmetrical capability and post the upload (that's for sure)!
here is the program: http://aloan.site90.net/pfmaker.zip

pfnew.png

 

If you have MMF2 or Fusion 2.5, and would like to jump in to help sort it out, my PF app maker file is here: http://aloan.site90.net/pfmaker.mfa

The company behind the app:

http://www.clickteam.com/clickteam-fusion-2-5

This program is made so it is easier for game makers to visualize their PF and Player art before writing them into code!

It only supports 7 PF and 7 Player colors, but more colors can be added later using the Pain.net program

This is a new screenshot of a first serious mirrored playfield art with a player1 on it (to mirror and add a background, I used Paint.net)

pfnew2.png

Edited by Aloan
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