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Asymmetrical rooms

One of the weird quirks of the Atari is that, while there are some registers to control the playfield layout (so you don't have to "chase the beam" to draw the entire background/playfield), there's only enough registers for half the screen, so it repeats the same graphics on both halves of the screen. There's another register that lets you determine whether it should be mirrored or duplicated.

Some games get around this by updating that register in the middle of the screen (which I also do when I'm drawing the subscreen map), but with the other stuff I'm trying to display (multi-colored main character, multiple enemies, missiles, etc), I don't really have time to do that. (as a counter-point, see the game Super Cobra, where they manage to cram that all in along with updating the background, although they have some clever limitations on movement to simplify things very slightly)

I've read bad reviews about this game, but I'm convinced the programmers are geniuses.

ANYWAY, my solution in Anguna is just to force every screen to be symmetrical (other than doors/walls on the far edges, which I fake with the Ball object). This makes for slightly less interesting room layouts, but makes my life a lot easier.  Except that my overall world design called for (at least) 2 rooms that broke that rule, and needed to be asymmetrical.  I had punted thinking through the design of how I was going to make these rooms work, assuming I'd come up with something eventually.

And so I did.

The 2 rooms are mirror images of each other, but not symmetrical themselves. It was a place where the river turned a corner:

How did I accomplish this, you may be asking? (If you are crazy enough to still be reading this)  I cheated.  The first half of the cheating is what you don't see, a grass-colored rectangle "enemy" that's just sitting on the left-hand side, hiding the river from view. Here's a similar picture of the room while I was working on it, and had the enemy colored red for debugging:

That accomplished half of what I needed -- making it look asymmetrical. But the hardware-based collision mechanism still knew I was walking into the playfield when I tried to walk through it. So I had to add a special exception in my general collision-processing code, so that playfield collisions in this particular region of these two particular rooms just didn't get counted.

The biggest drawback of cheating this way is that I can't have other enemies in this room -- I only allow one type of enemy per room, and the grassy overlay is using up the enemy for these two rooms. But that's ok -- I don't mind a few rooms here and there with no enemies in them. And I managed to get my asymmetrical rooms working.

And now, partially because it visually shows off my progress, but mostly because I'm obsessed with maps, here's the world map so far. It's about 1/4 to 1/3 of the total world that I have planned out.


sverx said…
Believe it or not, I've read the post until the end. And I'm amazed at what you're doing! :)
Igniz said…
Absolutely brilliant, nice way to come around the system's limitations. It has its limits and drawbacks, as you say, but the benefits far outweight them. I'll be waiting for more news about the project, keep up the good work.

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