Atari VCS Myst "Demake"

How much of MYST can you run on a 4k 16k Atari 2600 cartridge?


I was doing some Atari programming and thought I'd try out Myst. It's nowhere near a complete game, for that check out my Apple II demake version

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Here's a video of the gameplay for version 1.2:

Graphics Notes

The game engine uses ZX02 compression for each scene. I intentionally limit the compressed image to 256 bytes, which means I sometimes have to simplify the graphics to fit. Each scene has an asymmetric playfield. Graphics are 40x48 to simplify things a bit. Each line can be two colors, foreground and background. We fix the background to a single color. The foreground color can change each 4-line block. I use sprite1 as an 8-block wide source of additional color, so one extra color per line but only in that area. You also get an optional vertical line (missile0) which is the same color as the pointer. The engine possibly has provisions for the left/right side of the screen having different background colors but I haven't enabled that yet.

When uncompressed the graphics are 448 bytes which are temporarily stored in the 2k RAM supplied by the E7 cartridge (by default a 2600 only has 128 bytes of RAM).


Note: these were captured with the Stella emulator.

If you want to see screenshots from the original 4k proof of concept you can find them here

System Requirements


Disk Images


How to Play


Development Notes

12 August 2022-- Release v1.2

Now you can get to (and activate) three of the marker switches, plus you can investigate the red/blue books in the library. This involved making the book-drawing code generic which was a bit of a pain.

I'd estimate the cartridge is about half full now.

10 August 2022

Now up to 18 different locations you can visit. Need to start adding back the code that lets you grab objects.

5 August 2022-- Release v1.1

Everyone wants to see more levels, so I'm learning how to use an E7-style bank switch cartridge (16k ROM / 2k RAM). I'm hoping I can put a decent amount of Myst island on it. The kernel/engine I have takes 448 bytes for each screen, but I am using ZX02 compression to fit a lot more in (though it's tricky decompressing to the RAM). The compressed data has to fit in 256 bytes per level, which can be tricky for complex levels.

I've got the 4k version more or less transferred over (though I had to simplify some of the levels) and you can very barely walk about now. It should be more interested as I find time to add new levels.

29 July 2022-- Release v1.0

Powered through and did a 1.0 release. As always there are probably more important things I should be working on, but it's hard to not work on things until I get at least one release out the door.

Most of the work was adding animation to the cleft and book scenes, optimizing size down, trying to approximate the linking noise, and work on the arrival screen. Not entirely happy with how the arrival screen turned out but was running low on ROM so some compromises were made.

28 July 2022

Finished the clock scene. Redid a lot of the design as I've learned more about how the VCS works. Also put together the rocket graphics. Trying to have a 2-scanline kernel if possible but keep rolling over to 4-scanline as I run out of cycles.

27 July 2022

Got the linking book in decent shape. Feel like I've been decently clever with it.

26 July 2022

Working on the star cleft. Wasted a lot of time trying to make nice looking stars, really should look up how games like Solaris do it. Was trying to have an HMOVE of 7 and then skipping 8 scanlines so things were relatively prime, but didn't really work out that well.

24 July 2022

Got secret collect more or less finished so back to working on Myst. It was too ambitious a project to start with, things are going a bit easier now that I've learned some things.

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