The other day, being unable to find a suitable open-source text editor for cpmish, I sat down and wrote a simple vi-like editor. It took nine hours. I have it all on video.
This was a marathon. My original plan turned out to simply be not fast enough: I’m using the Amsterdam Compiler Kit compiler, because it’s the only one which will generate 8080 machine code, but the code quality isn’t good and is very slow. So partway in I had to redo the entire display layer when I realised that I couldn’t do screen updates fast enough. (It would totally have worked had I written it in raw machine code…) I also took several other wrong turns later, all of which wasted time. But I did eventually produce an adequate, working text editor, supporting most of the basic vi editing commands I use.
- 00:01:30 Boilerplate
- 00:05:30 First, broken version of the refresh code
- 00:58:35 Start work on the editor
- 01:36:00 Initial text rendering works; start work on command loop
- 01:36:30 Realise that I need direct BIOS access and I add support to the ACK
- 01:54:40 Continue on the command loop and cursor movement
- 02:39:00 Realisation that the screen refresh code won’t work
- 02:44:00 Start ripping out the refresh code
- 03:07:00 First redraw with the new refresh code
- 03:22:00 Horizontal cursor movement works
- 03:48:30 Vertical movement works, slowly
- 03:56:57 Dinner break, decision to drastically simplify editor model
- 04:28:05 Cursor movement with the new model works
- 04:51:10 Cursor movement with the new model works quickly
- 05:00:00 Insert mode works
- 05:21:30 Motion by words works
- 05:37:45 Repetition count works
- 05:49:40 Inserting newlines works
- 06:30:00 Scrolling works, up to a point
- 07:17:30 Lots of commands work, start thinking about batching redraws
- 07:34:45 Notice a hanging problem with scrolling over big lines
- 07:39:30 Tea break, remove all the batching redraw stuff
- 08:07:08 Finally figure out the horrible scrolling bug
- 08:53:15 Saving documents works
- 09:09:07 Simple colon commands work
Right now it’s a shade under 10kB, allowing files of up to 49kB on a Kaypro II; that’s not bad. If I were to recompile it with sdcc it’d be both faster and about half the size but sdcc’s CP/M support is very poor and I keep running into code generation bugs, so I’m sticking with the ACK for now. (Maybe when z88dk reaches Debian…)
The main missing features are search and a yank buffer. Neither would be hard to add, although I don’t think this will ever get regular expressions, and the yank buffer is most easily implemented by keeping the buffer on disk; that’d be slow, though.
Since doing the video above I’ve done some polishing, bugfixing, and a few more features. Terminal support is now factored out into a standalone library, making it easy to support multiple terminal types, and for the Kaypro II and NC200 it supports the erase-until-end-of-line control code, making redraws a lot faster.
The code is BSD-2 clause licensed, meaning you can pretty much do with it what you like!