Retro Festivities Abound in Creating a Christmas Scene on the ZX81
Bringing yuletide cheer to the ZX81 screen, one line of code at a time.
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.
# Generating Christmas spirt.
Fitting the mood, I started with the tree. Based on a routine posted for the tree compilation a few years ago, I modified it to work on the ZX81. The ZX81 can’t execute multiple commands on a single line. This required me to expand the routine a bit and center it on the page. Done, right?
Well, not quite. I liked an idea from another post that used varying snowflake sizes. I refactored the program into logical sections and added a new routine to display the snowfall. It’s similar to how I’ve generated stars in other programs. In this case, I used RND and a string to print the flakes.
With that look done, I then worked on the message. Again, it’s much like other animations I’d done as a teenager. I went through a few iterations until I settled on the final message. The message is in inverted characters with rotating stars. Simple enough to make using a pair of print statements.
# Comments and structure.
For some reason, I decided to focus on program structure. Something that is very different than most of my programs. I have built programs with aesthetics before, but rarely. I was in the mood.
After getting the tree to work, I moved the routine to a subroutine. The initial section of the program consists of a list of routine calls using GOSUB. I reordered things a bit, first printing the screen, then the snow, followed by the tree, and finally the message.
There is one I don’t call directly. That one saves the program so that it will run when loaded. I used RUN 70 to start the saved program. Once the message loop finishes, the program restarts with another RUN. It looks repetitive, but I don't have many options in ZX81 BASIC.
# Merry belated Christmas.
And with that, I’ve conveyed my message. It’s late as I was busy spending time with the family and doing other things. Better late than never. I still like the look, but I would have liked to animate the snow a bit. The ZX81 would be pretty slow with that. It gives me something to work on next year.
Originally published at https://www.reids4fun.com on December 30, 2023.
