retro-ps

Classic PostScript interpreter binaries running inside a CPU-emulator sandbox, on the command line or in your browser.

The HP C2089A "PostScript Cartridge Plus" turns an HP LaserJet II/III into a PostScript printer. It contains a 2 MB ROM with Adobe's reference Level 2 PostScript interpreter (version 2010.118). We feed it bytes, emulate the 68k, fake the bits of the printer's main board it expects to be there, and collect each page it draws – and its status/error messages.

The original cart only renders at 300 DPI, with a 0.25" margin, on some pre-defined paper sizes. We generalise on top of that:

• Any resolution.
• Any paper size.
• Any lpi for the screening dots. We default to 1/5 of the printing dpi.
• No margins.

The only hard limit is 16,000 pixels in each dimension.

CLI

cargo build --release
target/release/retro-ps some.ps -o /tmp/out

Output is one 1-bit grayscale PNG per page; the cart's PS-side print / == / error output goes to stderr unprefixed, like a real PostScript printer.

Flags:

<INPUT>	PostScript file to render (positional)
-o, --output PREFIX	output prefix; files land at <prefix>_NN.png (default page)
--rom PATH	use a different ROM image instead of the baked-in one
--paper-w PT / --paper-h PT	paper size in PostScript points (default 612 × 792)
--paper-dpi N	render DPI (default 300)
--paper-w-px N / --paper-h-px N	raw pixel override; wins over --paper-w × DPI
--lpi N / --screen-angle DEG	force halftone frequency / angle via a setscreen prolog
--lj3	mimic the original LaserJet III: 612 × 792 at 300 DPI with the 0.25" hardware margin and imageable-area crop
--exit-after N	stop after N captured pages
--max-insns N	hard cap on cart instructions executed
-v, --verbose	also print emulator boot/teardown chatter, LCD status text, and per-page write notices
--ram-snapshot PATH / --ram-snapshot-force	dump cart RAM to disk for offline inspection

Browser

cd retro-ps-web
./build.sh                            # wasm-pack into pkg/
python3 -m http.server 8080
open http://127.0.0.1:8080/

Drop a .ps file onto the page; the wasm runs in a Web Worker so the render doesn't block the UI.

A live build is at https://www.pagetable.com/retro-ps/.

Internals

A few things worth knowing about how this differs from a real cartridge in a real LaserJet:

• CPU and RAM. The emulator's 68020 sees more than the original 68000's max. 16 MB of RAM here. That headroom is what lets the cart render high-DPI pages without us rewriting its allocator.
• Pixel ceiling. The PS interpreter's clip operator caps content at about 16,000 device pixels per axis. That's a cart-firmware limit we can't paper over without patching the ROM, so the practical DPI max scales with paper size — about 1450 DPI on Letter, less on bigger paper.
• No mainboard, no engine. We have the cartridge ROM, not the LaserJet III's mainboard ROM, and we don't have a print engine at all. The emulator stands in for the half-dozen low-memory soft-traps the mainboard would have provided (printer-model byte, IPC byte stream, engine status polling) and fakes the engine-done interrupt so the cart's state machine can move on to the next page.
• Halftone scaling. Adobe hand-tuned the cart's halftone cell for 300 DPI; above that the default cell renders too sparse and grayscale fills look chalky. We inject a DPI-scaled setscreen prolog so the cart builds an appropriately-sized dot itself.

Author

Claude, directed by Michael Steil <mist64@mac.com>.

License

Public domain.