Another year and another Vintage Computing Christmas Challenge (VC3 for 2024). I rushed a bit to get mine in so I do feel it wasn’t as short as possible. I did take a somewhat unique route to solving the problem which makes the build more interesting. I made an auto-run version for Present so you could see it in action.
The year is almost over and time to close out the year with a short program. Watching some videos on character displays in UNIX, I was inspired to create my own version of Hello World. This version scrolls through a stream of random digits until the message is displayed. How fun is that?
One thing I hadn’t done before on the ZX81 was hires graphics. There are numerous reasons, but in general it was because I hadn’t tried. That changed after being encouraged in my ZX81 group to use with with Mandelbrot Set program. So I did.
After wrapping up the last print scroll routine, I immediately dove into improving it. While functional, the original version felt a bit limited. With this update, you’ll find more flexibility in printing displays, though at a slight cost to speed.
As plans go, I actually have a few programs teed up to share. Many are smaller programs that I could work on here and there. Occasionally, I run across an idea that upends those plans and I end up going another direction. So, here we are in September with a math program for the Collatz Conjecture.
Sometimes, you do things out of necessity. I spent an inordinate amount of time working on adding automatic scrolling to a PRINT command. In fact, I haver another version of my print scroll routine I’ll talk about later. But this is about a utility program. A way to print out BASIC code in hex. And this article is about what I did and why.
Finding inspiration again from my programming groups, the idea of an infinitely scrolling screen of text came up. There were a couple of different solutions posted, some quite ingenious. I had done something similar in the past, but this time I used a bit of machine code magic to create a more flexible solution. The result is Print Scroll.
My ZX81 programming has taken a back seat of late as I focused on other activities. Whether family, work, or the latest video game update, I haven’t put as much effort into finishing projects. For this month, I decided to focus on tackling an interesting problem, emulating the PRINT USING command.
Soon after sharing my Maze Generator for the ZX81, it was obvious that something didn’t quite click. I got a few comments about the maze didn’t work or that didn’t look right. It was clear the '70s style teletype display wouldn’t cut it. Fortunately, I could fix that.
Something I’d been itching to do is write a maze generator. Even though they seem simple enough, for some reason, I struggled to code one. With so many different algorithms out there, the sheer number of choices can be overwhelming. It wasn't until I took a vacation that my mind settled down enough for me to finally tackle the task.
I had forgotten about this Black Hole program until I ran across it while cleaning up some directories. It is a conversion, not an original, program that was shared on one of my BASIC forums. It doesn’t look quite as good as the original, but it was interesting to see what the ZX81 could do with its simplistic graphics.
While on vacation, I spent some relaxing time converting my Kimmie Fish BASIC program into something a bit more interesting. In addition to the normal speed improvements, I wanted to give it an aquarium like feeling with bubbles and depth. No color here, this is all stock ZX81 graphics. Only thing needed is the requisite 16K memory pack.
Reading posts in the BASIC group I follow, I was I was inspired to write my own version of the kimmie fish animation for the ZX81 computer. It was such a cute animation that I had to see if I could replicate it. Although not quite the same as the original, the spirt is there.
For December, I decided to embrace the Christmas spirit. Inspired by group posts, I created a Christmas tree and snow scene. It needed a little flair, so I added an animated message to the scene. Very retro program for my ZX81.
I've talked about Tower of Love before, but that was a much different version of the game. That version was all about the intro screen and my initial attempt at the story. I even showed another design I had made. To my surprise, I had a third version of the adventure that I started. Time to share!
Pitfall! without the peril, with this accurate ZX81 simulator.--> While contemplating what ZX81 program to write about this month, I completely forgot that I had created a Pitfall! Simulator. It began as a fun project to occupy my time during winter break. My initial goal was to recreate David Crane's LSFR (Linear Feedback Shift Register) in Z80. However, after learning more about its functionality, I took the project much further than I had originally intended.
A recently posted meme reminded me of the silly things we did on computers. In the early eighties, most computers came with BASIC as their default OS. A common starting point was a s simple “hello world” program. But almost as often, someone wrote something a bit more personal. This is my tribute program to the “I was here” concept of those days.
I saw the Commodore 64 maze generator for years, but ignored it on my ZX81 for different reasons. For one, the characters needed didn’t exist on the ZX81 keyboard. The other was the lack of automatic scroll. Undeterred this month, I created my own version in Sinclair BASIC. I’m quite happy with the results, even if not quite the same.
In my final article about Mandelbrot sets, I’m sharing the hybrid program built from the last two. After finishing the chunky graphics version, I envisioned a merged version. This split graphic version is a nice compromise to showcase the beauty of the fractal.
After completing my Chunk Graphics mode, my thoughts went to how best to use it. My first idea was something new, such as a flight simulator. After pondering, I stuck with something current by modifying my Mandelbrot Set program. With three gradients, it would be an interesting use of the mode.
Out on a run back in November of last year, I had this idea to create a 3-color screen mode of the ZX81. The idea was to use the checkered, or gray, graphic characters to add a third color. After reading about the C64 color modes, I called it chunky graphics as an homage to its wide pixel format. The pixel’s are chunky due to the 2x1 ratio and not being square. Let’s dig into the details.
After finishing the basic version of the cat animation, I wanted to improve the frame speed. This meant converting from BASIC to machine code. My first thought was to do the conversion with MCODER II. I dropped that idea, deciding to focus on a custom z80 Assembly version. Ergo, cat written in assembly or Fast Cat is, well, a faster version and a bit more.
![ZX81 Rain, Chroma ZX81 Screenshot, 2023 by Steven Reid]](https://www.reids4fun.com/images/zx81/zx81rain-2023-zx81-chroma-screenshot-by-steven-reid-320x240.png)
The holiday's provided me a nice break to enjoy writing code. During that time, I revisited my digital rain program. For ZX81 Rain, I cleaned up the colors and added a little randomness to where the drops start. Nothing super exciting, but the overall effect is much nicer and looked good in both black/white and color on the ZX81.
I had this idea the other day. One of the problems I’ve had with the ZX81 is printing numbers, which is pretty slow. Due to this, many of my games avoided printing them. delaying showing score until after play has ended. My idea was to try to find a way to speed that up. Not only did I find a way, I decided to implement it in an older game of mine: E.T.
I’ve been on a retro computing binge lately and was recently watching one on programming on what it was like to program in the 80’s. Having lived and programmed during that time, I know full well what that was like. But the narrator was showing off an Apple ][+, a computer I didn’t own. Although I programmed on an Apple ][ in high school, my memory of it is vague at best. But what was really interesting was what he was programming: a snake game. Being something I’d never tried myself, I thought now would be as good time as any.