When designing ROSE-8, I realized that the last 8-bit CPU architecture I had learned about was the Nintendo Game Boy, via Eevee’s Cheezball Rising series. That gave me a goal for ROSE-8: implement a system that could display graphics and receive real-time button presses, and thus play games. As I hinted last time, I did indeed manage to achieve this! Introducing the Game ’by Color (pronounced like “Game B Color”).

% xcodebuild -scheme App
% swift run rose8-as Examples/super-maze.rose8 -o $TMPDIR/super-maze
% open -a "Game 'by Color" $TMPDIR/super-maze

TLDR: You can check out the repository and build this Mac app yourself. If you’re very enterprising, you can even write games for it. Non-games too, I suppose.

EDIT: I added an X11 implementation for Linux users as well, under swift run xgamebycolor.

There were several different pieces that went into this:

• The ROSE-8 “CPU” needed basically no changes from what was already needed for console interaction, which was nice.

• The graphics system was the biggest piece. For this I basically copied what the Game Boy does, referring to a bevy of resources which I linked in the readme. I did simplify it some, but the gist is still the same: there are color palettes, and tiles you can draw using those color palettes, and a background grid of tiles, and sprites that also use the tiles.

• A realtime system needs a timer, mainly for animation but also to avoid zipping across the screen if you hold down the “right” button too long. I went with a simple design I discussed with ROSE-8 co-conspirator Cassie: there’s a counter in memory that goes up at a program-defined interval, and programs can WAIT on that counter to “consume” a “tick”. This works pretty well for what I’m doing, but I can see it being limiting in other instances.

• Of course, it’s not a game if you don’t have inputs. I wired up the keyboard to cause bits of memory inside the ROSE-8 to change when you press certain buttons. This is what I think of as “computer plumbing”: connecting two self-contained systems to make something work. It wasn’t hard. (Actually processing the input inside the ROSE-8 program was a bit trickier, though.)

If you’re interested in any of these pieces for one of your own projects, I suggest checking out the revision history. I think it’s pretty clean, even if it comes in big chunks.

The screenshot at the top is of a maze game, the same game I used to demonstrate console mode. It really works! (Fun fact: the screenshot from last time was the test pattern Eevee used during her own initial forays into Game Boy Color programming.)

I think this is about it for ROSE-8 adventures for me. While I do still have ideas for new instructions to make it easier to program (…in bare assembly…), I’ve accomplished all the basic things I thought about when first starting the project¹, and I have other projects and blog posts I’d like to get to. But it was a fun month’s diversion, and I appreciated both the challenge of operating under (virtual, self-imposed) limitations and the opportunity to learn about and make things I hadn’t before. If you have time, I highly recommend learning about and making things you haven’t before.

This entry was posted on February 04, 2020 and is filed under Technical. Tags: Source code, ROSE-8