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experts; atari 2600 display hardware
rants Posted 2003-02-28 16:03:49 by Jim Crawford
I've been reading recently, and it's actually pretty interesting. It never fails to amaze me that just about all fields of human endeavor, even those you usually don't think about, have become deep enough to produce and require experts.

Thinking about that, I wondered whether cooking experts get indignant and write huffy writeups when cooking is depicted obviously incorrectly in film or television. The idea struck me as funny, which made me feel a little bit guilty, because it's really no more nerdly than, for instance, me getting irritated at this page of fake Atari 2600 games because the fake screenshots are far too complex for the real Atari 2600 hardware to display.

In fact, it's probably a lot less nerdly.

But come on, people! If you're gonna make a joke screenshot of a fake Atari 2600 game, at least do the research to find out whether the hardware can even display what you have in mind!

Now, okay, this guy isn't completely hopeless. Look at Peabo Bryson's Cow Tipper. He obviously put some work into it. He even put in the little black lines that appear on the left side of the screen when you hit the hmove register.

But he scattered them all over the place at random! It's like the guy wanted to draw some human faces, noticed that human faces occasionally featured crow's feet, and pasted some crow's feet all over the cheeks and forehead.

Look, friend. I like you. I'll make it easy for you. You don't have to bother to go anywhere to do the research. I'll give you quick rundown right here. And next time, you have no excuse!

Here we go. The Atari 2600 display chip, called “Stella” by those who love it, has only enough memory to render one scanline at a time. Every scanline, the software must update the contents of video memory. On any given scanline, the chip can display the following:

  • A 40 pixel Playfield. There are only 20 bits allocated for this, so officially it must be mirrored or doubled. In practice, even games as primitive as Combat implemented a mid-scanline hack to display an asymmetrical playfield.
  • Two 1 pixel missiles and one 1 pixel ball. These names were chosen based on the assumption that the system was mostly going to be rendering pong variants.
  • Two 8-pixel-wide players. These are monochromatic. They can be stretched horizontally so that every “pixel” takes up two or four actual pixels, or they can be doubled or tripled at three possible distances.
Within limits of CPU power, the programmer can alter any of the data specifying the colors, bitmaps, and locations of all these objects on a per-scanline basis.

The “players” are the only source of anything approaching high-resolution graphics. This means that high resolution objects can have at most two colors per scan line. One color per player.

Mid-scanline raster effects are possible, but difficult, as the electron beam advances at around 3 pixels per CPU clock cycle. The most common trick is probably the aforementioned trick to create asymmetrical playfields. Another common trick is to create very wide sprites or six digit scores by interlacing both player sprites, each tripled-up at “medium” distance. There is just barely enough CPU time to update the next digit before it is displayed.

So. With our newfound knowledge, let's do an analysis of one of these screenshots, say, Bosom Buddies. I'm not even going to go into whether this could actually be rendered real-time, as a game. Let's just see if it's possible to write a program to display this as a static screen.

At the top, we have a numeral 1. So far so good. It has some slight vertical overlap with the old woman nearby, but only when she's just one color. Then we have the mountain range with the vertical sunset gradient in the background. I haven't counted the number of horizontal pixels, but it looks reasonable. The old woman has three colors occasionally, but we can give the artist the benefit of the doubt by assuming he's not only overlaying two sprites, but also using the missiles to add the occasional dot.

The six skulls. That's fine. Both player sprites are tripled up. The windows and the ladder-looking thing, fine. That's low-res art. The purple bricks would seem to be impossible at first, since there can only be two background colors, but perhaps the programmer is using the free player sprites to render them. So far, so good.

But then, tragedy strikes. On the very same scanline as Tom Hanks, we have a shirt, an anvil kind of thing, the ladders, and two purple bricks.


That's a playfield and five complex objects at once! We could stop our analysis right here, but let's glance at the next few scanlines to see if it gets worse.

Oh, hey, it does. This “Susan B. Anthony” banner? Egregious! But wait, it's all one color, maybe the developer is applying the big-sprite trick? I'm afraid that's impossible -- it's far too wide. Each of those letters, though they look like they're three pixels across, are actually at least six, because you can't both multiply and stretch the players.

The rest of the image looks okay, except for two more of those dastardly purple bricks floating alongside Peter Scolari.

Oh, and that line of crap along the right edge of the screen. What's that supposed to be?

[link to this] [See more on “rants”]

If cooking was depicted as computers are
Posted by Anonymous (Craig Timpany) on 2003-03-01 19:03:28
If cooking was depicted on TV as incorrectly as computery stuff is:

* Cookery experts would become plot devices in all sorts of unlikely ways. e.g. "Oh no, we need to sabotage this oil rig -- Wait, Bob's a chef, he can cook us a bomb!"

* This would be the basis for gratuitous countdown scenes: "We've only got 3 minutes before that bomb is golden brown!"

* The cookery experts would spout meaningless lines filled with incorrect jaron. "The flan-spatula is poached with tumeric! We'll have to refridgerate."

* Occasionally foods would become so delicious that they would develop malevolent intelligence and turn against humanity. "Insolent humans!! How dare you challenge the invincible, ever-watchful Chocolate Gateau?"
re: If cooking was depicted as computers
Posted by Jim Crawford on 2003-03-02 15:49:17
Great stuff. Now I feel better about laughing at those imaginary, indignant culinary experts, too. Get a life, you nerds!

Thanks, Craig!
speaking of culinary experts....
Posted by theexaltedkarphoozi on 2003-03-21 09:20:23
has anyone here seen the Iron Chef on TV? it's japanese. it's like a cross between a regular cooking show and a boxing match (and, no, i dont mean they attack each other with dead octopi). it's actually quite amusing. they have instant replays and everything. and the food is tasted by a panel of judges, which inevitably always contains a perky japanese actress, a japanese distant young actor/singer, an frumpy japanese journalist (m), and a cranky old japanese culinary critic (f). its great! they use subtitles and they're dubbed! i will quote the perky actress one time, when the theme ingredient was salmon and she was presented with salmon roe ice cream, "Iron Chef, how could you?" of course, the show is fun because the set up is ridiculous.
re: speaking of culinary experts...
Posted by Jim Crawford on 2003-03-21 13:53:13
I've heard about Iron Chef. I've never seen it, but it sounds like a great idea. Is it on U.S. television?
I made those fake 2600 screenshots.
Posted by Anonymous (Jason Torchinsky) on 2004-03-09 14:01:12
Jeezis, buddy, relax!

When I made these screenshots, for, I should point out, my COMEDY group, I sort of half-expected some shockingly painful geek to call out my inconsitencies with what real 2600 hardware could do. Looks like I got my wish.

Look, I know what 2600 hardware is capable of. I know it's powered by a 6507 (a 6502 with reduced memory addressing) I know about the Stella chip, I know about the 20-bit playfield, and the HMOVE lines at the side of the screen I know all about. I'm a bit of a geek myself.

I also know I was making these as a loving joke. And that's the key point here. Yes, I didn't always use symmetric playfields. Yes, sometimes I put too many sprites on screen. (though multiplexing could, in theory, make it possible but flickery). What I did is I just picked some of the most distinctive traits (wide playfield pixels, HMOVE lines, sprites with colors in horizontal bands, etc) and used those few rules to make screens that felt like Atari 2600 screens. Because that's all that was needed to get the joke across.

Now, just for a moment, let's look at your rant: you went scanline-by-scanline to deconstruct whether or not such screens were really in fact possible. Then, even worse, you wrote about it and published it here. Are these the actions of a healthy person?

It was a joke. They're fake. We all believe you that you know lots about how Atari 2600 games work. Mission accomplished. Enjoy all that trim you'll be getting now that your prodigious 2600 game-creating knowledge is widely known. You've earned it, soldier.

Oh, and thanks for the link!

re: I made those fake 2600 screenshots
Posted by Jim Crawford on 2004-03-09 17:39:03
 Now, just for a moment, let's look at your rant: you went scanline-by-scanline to deconstruct whether or not such screens were really in fact possible. Then, even worse, you wrote about it and published it here.

I would be disinclined to call slapping something on my blog "publishing" :)

Also, you've got things out of order. First, I determined that most of the screens were not possible by, y'know, looking at them. Then, I picked one that's not so obviously wrong to dissect for the benefit of the viewers at home.

 Are these the actions of a healthy person?

Now wait just a darn minute, are you saying I'm unhealthy just because nothing can meet my impossibly high standards?

 It was a joke.

I realize that. For what it's worth, even though I categorized it as a rant, this post was also fairly tongue-in-cheek (and, yes, it was also an excuse to show off my Atari 2600 knowledge). I was hoping my excessively shrill tone would read as part of that, but I realize some people really do talk like that.

 Oh, and thanks for the link!

No problem. Cheese me off again and you'll get another!
re: faker
Posted by Anonymous (sugigrl) on 2004-03-13 18:33:41
wow looks like jason torchinsky's the only one allowed to be funny on the net, feeling threatened are we?
Posted by Anonymous (Christo930) on 2010-02-13 20:43:22
Stella was the codename for the console. The graphics chip is called the TIA (television interface adapter). I think you are greatly underestimating the atari 2600. Have you ever seen the supercharger version of frogger? All the SC adds is ram. There are many 2600 games which really pushed the sytem well beyond anything the designers ever dreamed of.
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