Overview
Not a reimplementation and not a screenshot: the actual TempleOS kernel, its HolyC JIT, its graphics, its games. It resumes from a RAM snapshot of the booted desktop, so the machine is up in roughly four seconds, and the 3D games run at the 30 fps they were designed for.
Why it had to be emulated
TempleOS is 64-bit only and is its own self-hosting compiler, so there is no cross-compiling it to WebAssembly. HEMU takes the other road, and takes it in TempleOS's own language: an x86-64 emulator written in HolyC, about 1,300 lines, compiled to WASM by a from-scratch HolyC compiler written for this project. It emulates only the hardware TempleOS actually touches, which is a short list: PIC, PIT, HPET, PS/2, ATA and the VGA DAC.
Where the speed comes from
Three layers, and the first is the joke that works:
- An x86-64 to WASM block JIT that compiles hot guest code to native WebAssembly at runtime. It is the same trick TempleOS's own JIT plays, one level up.
- High-level emulation of the hottest render routines, the window compositor blit and the games' span fillers, each shadow-verified bit-exact against the emulated version before it is allowed to take over.
- A worker engine, so the emulator never runs on the main thread.
The guest clock is paced to real time, and keystroke timing feeds the OS's God apps with real entropy, which is what TSC sampling did on the hardware Terry wrote it for.
What you can do in it
Write and run HolyC in an in-page editor, compiled natively to WASM rather than emulated. Export a snapshot of the whole running OS and reload it later to resume exactly where you were, or export the C: disk with your files on it. Pause the machine, guest clock included. Draw a God word from the oracle, with entropy from your own typing.
TempleOS is public domain. It was written by Terry A. Davis.