GoKawiilZX Desk
A graphical desktop for the ZX Spectrum 48K, written in Z80 assembly.
Overlapping windows with a z order and focus, pull down menus, a heap, an event queue, a storage layer with swappable backends, dialogues, controls, a notepad, a clock, a calendar, a two pane file manager, and a settings panel that actually changes things. It all fits in 48K on a machine from 1982, and it can drag a window inside a single 69,888 T state frame.
It runs on the real thing, not just an emulator.
Why
Back in the eighties I wanted an Atari ST and couldn't afford one. What I really wanted was GEM: the desktop, the windows, the menu bar that was always there, the feeling that the machine was a place rather than a prompt. I had a Spectrum instead, and I spent a long time wondering how much of that you could do on it. I started writing bits of it, and never finished.
So this is that, finished. It isn't a port of GEM and doesn't pretend to be. It's what the idea turns into when you push it up against a 3.5 MHz Z80, 48K of RAM, a one bit display with attribute clash, and a video chip that steals cycles from the CPU while it paints. A lot of the answers turned out to be more interesting than the question, and nearly all of them came from measuring the machine rather than reasoning about it.
It's a fun project and a labour of love, and the reason it's written up at this length is that the measurements are the useful bit. If you're building something on this hardware, the numbers below cost me a lot of evenings. They're yours.
What it does today
Windows Overlapping, z ordered, movable, resizable, with title bar, close box and grip. Focus is the front of the z order, so raising and focusing are one action. Menus A permanent menu bar with pull downs, save under, and hit testing. Input Kempston mouse, Kempston joystick, and the full keyboard matrix decoded across three tables with repeat. All of it arrives as events. Events A sixteen slot ring. The main loop contains no window specific code. Storage A registry of backends behind six vectors. RAM, tape (via the real ROM loader), and the 128K's spare banks as a RAM disk. esxDOS has a reserved id. Memory A real heap with an owner byte, 8,112 bytes, allocating window buffers sized to their windows. Applications A descriptor with init, event and paint, plus per instance state swapped in and out. Notepad, clock, calendar, commander, about. Persistence Settings written to storage with a magic byte and a version, and read back at boot.
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