This is the program for the eleventh RetroBattlestations BASIC challenge.
It seems like fractals have become popular again, so I present to you The Mandelbaum Set.
This program will iterate over and over chanting along, generating smaller and smaller chants using matrix transformations. While Applesoft supports using 2D arrays, not all BASIC dialects do and since the matrix is only 3x3 I simulated a 2D array using very simple math (mathsfsh for you British people). Like any good fractal rendering program, it's very slow. You're also going to want a decent resolution - character block graphics really isn't going to cut it. In fact outputting to a pen plotter may give some nice results, if you're up to rewriting the program to do it!
Since this uses techniques I've never used before –namely matrix math– I chose to write the program in Python and get it working there first, and then convert the program to BASIC. Keeping track of 2 letter global variables in BASIC was more challenging than usual. Having to deal with line numbers also provided some additional challenges. And of course there were the usual simple mistakes during translation such as typos and forgetting about managing all my loops myself. But overall I think making the program work in Python first probably was the way to go. (Someone should write a Python to BASIC compiler!)
As always, I did my best to write the subroutines in a way that they might be reusable as some sort of "library" for other programs you may decide you want to create.
For more details about the challenge, check out the post here:
Before you start working on porting the program and changing things to work on your machine, try running the Apple II version in an emulator (or real hardware if you are so inclined) so you can see how the program works and what it does. The advantage of testing in an emulator is that many emulators will allow you to easily paste text as if it were keyboard input so you don't need to hassle with manually typing it in or figure out how to convert the listing to a tape or disk image.
See List of Computers With On-Board BASIC
- Send output to an external high resolution device
- Compensate for non-square pixels
- Turn it into some kind of continuously looping animation
- Reduce the number of redundant calculations and make it run faster
When typing the program in you can leave off any lines which begin with REM, they are not needed for the program to run. On many platforms you can leave out the whitespace between keywords and operators. IBM BASIC is not one of those however.
Note: On the TRS-80 Color Computer and BBC Micro you need to include the spaces around any IF, AND, OR, or THEN statement.
If you make a mistake and don't want to retype the entire line, most of the BASICs have a way to make corrections.
On Amstrad CPC, use AUTO to start typing commands. Use the arrow keys to move about the line. Exit the AUTO mode py pressing Escape. You can also start on a specific line by entering AUTO 100 (for line 100).
To go to the start or the end of the line use CONTROL+Arrow keys. You can also use SHIFT+Arrow keys to use the copy cursor. This is a second cursor that you move independendly, and will copy whatever is under it to the main cursor when you press COPY.
On an Apple II+ use LIST to print the line with an error, then use ESC followed by A/B/C/D to move the cursor one step at a time. Position the cursor at the beginning of the line, then use the right arrow to move over the line and fix the error. Be sure to arrow all the way to the end of the entire line before you hit RETURN!
On an enhanced Apple IIe, Apple IIc, or Apple IIgs you can also use ESC with the arrow keys. In 80 column mode (enter with PR#3) the cursor will change to a white block with a + in it, push ESC to drop out of movement mode.
Use LIST to print the line with a mistake, then use the arrow keys to move up to the beginning of the line. Each press of the copy key will type in the character under the cursor. Make any necessary edits by just typing on the keyboard and using copy to avoid retyping everything.
Like the others, use LIST to display the line with problems, then use the arrow keys to move up and make any corrections. By pressing shift-INST you can insert a blank character if you missed something. Unlike the Apple II you don't need to arrow to the end of the line before pushing RETURN.
Type EDIT and it will print the line on the screen and put your cursor at the beginning of the line. Arrow left/right and you can use Insert & Delete to make corrections. Like Commodore BASIC, you don't need to arrow to the end of the line before pushing RETURN.
Type the line number and then arrow up (FCTN+E) and it will enter edit mode with that line loaded. You can move within the line with arrow left (FCTN+S) and arrow right (FCTN+D) and move to the previous or next line with arrow up (FCTN+E) or arrow down (FCTN+X). You can delete the character under the cursor with DEL (FCTN+1) or turn on insert mode to insert extra characters with INS (FCTN+2). You do not need to move to the end of the line before pressing ENTER.
This has to be the best built-in BASIC editor I've seen so far! Just type EDIT and the entire BASIC program will be loaded into the built-in word processor where you can make any changes you want. Press F8 to exit the editor and go back to BASIC.
Having a hard time finding where all the BASIC keywords are hidden? Get Commander le Clef's Secret Encoder Wheel with an alphabetical sorted listing of keywords and the secret keypresses required to enter them.