MaximeRivest/Riddle

Source: https://github.com/MaximeRivest/Riddle

riddle — the diary of Tom Riddle, for the reMarkable Paper Pro

Write on the page with your pen. After a pause, the diary drinks your ink — your words fade into the paper — the page thinks for a moment, and an answer writes itself back in a flowing hand, stroke by stroke, then fades away.

No screen glow, no keyboard, no chat UI. Just ink appearing on paper.

This is the diary from the demo.

🪄 New to this? Start here

You need a reMarkable Paper Pro in developer mode with a launcher installed. If that sounds like a lot, it isn’t — remagic walks you through turning on developer mode and sets up everything with one command. Come back here, drop riddle in, and start writing to Tom.

Already have xovi + AppLoad? Install from the remagic catalog, grab the prebuilt bundle, or build from source.

Install with remagic (easiest)

remagic install riddle     # checksum-verified download → AppLoad
remagic config riddle      # settings form in your browser (+ QR for phone)

Then in AppLoad: tap Reload, then The Diary. Write, and rest your pen. (Or install it from the Store app right on the tablet.)

Install the prebuilt bundle

1. Grab riddle-<version>.zip from the latest release and unzip it into a folder: unzip riddle-*.zip -d riddle
2. Copy the folder to your tablet: scp -O -r riddle [email protected]:/home/root/xovi/exthome/appload/
3. Add an API key: cp oracle.env.example oracle.env in that folder and put your RIDDLE_OPENAI_KEY in it (any OpenAI-compatible key). Or skip it to use pi.
4. In AppLoad: tap Reload, then The Diary. Write, and rest your pen.

⚠️ This modifies your device. It runs as root, stops the vendor UI (in takeover mode), and drives the e-ink engine directly. It has only been tested on a reMarkable Paper Pro (ferrari, aarch64, OS 3.26–3.27). It may not work on other models or OS versions, and you use it entirely at your own risk. Not affiliated with reMarkable AS. Keep SSH access working before you install anything — that is your escape hatch.

How it works

 pen (raw evdev, full 4096-level pressure, hardware event rate)
   │ strokes
   ▼
 riddle ── idle 2.8s → commit page → PNG ──► oracle (resident LLM process,
   │                                          streams reply sentence-by-sentence)
   ▼ strokes (Dancing Script → skeletonized to single-pixel pen paths)
 display backend
   ├── qtfb        — windowed, inside xochitl (AppLoad app)
   └── quill       — full takeover: xochitl stopped, vendor e-ink engine
                     driven directly for instant ink (lowest latency there is)

• riddle/ — the app (Rust). Pen input, ink surface, handwriting synthesis (rasterize → Zhang-Suen thinning → stroke tracing → animated replay), the oracle process manager, and both display backends.
• quill/ — the takeover display host (C/C++). An epfb-re-style QImage-constructor interposition shim over the vendor libqsgepaper.so waveform engine, exposed as a small C ABI (quill_init / quill_buffer / quill_swap) that riddle links against with --features takeover. Also carries a small family of demos (scribble, a pen-to-glass latency test, plus map, image, and GIF renderers).

Gestures

The oracle (the “spirit” in the diary)

The diary’s replies come from a vision LLM that reads your handwriting from the committed page (sent as an inline PNG). There are two backends, chosen at startup — pick whichever you have:

Option A — any OpenAI-compatible API (easiest, zero setup)

Set an API key and riddle talks straight to an OpenAI-compatible /chat/completions endpoint. Works with OpenAI, OpenRouter, Groq, a local server — anything that speaks the format. No extra software on the tablet.

export RIDDLE_OPENAI_KEY="sk-..."                       # required
export RIDDLE_OPENAI_BASE="https://api.openai.com/v1"   # optional (default)
export RIDDLE_OPENAI_MODEL="gpt-4o-mini"                # optional; must see images
export RIDDLE_OPENAI_REASONING="low"                    # thinking models only
export RIDDLE_OPENAI_MAX_TOKENS="2000"                  # runaway guard

Any vision-capable model works. On the tablet these live in oracle.env next to the binary (see oracle.env.example, or just run remagic config riddle — it has one-tap presets for OpenAI, OpenRouter, and Gemini). Example with OpenRouter:

export RIDDLE_OPENAI_KEY="$OPENROUTER_API_KEY"
export RIDDLE_OPENAI_BASE="https://openrouter.ai/api/v1"
export RIDDLE_OPENAI_MODEL="openai/gpt-4o-mini"

Two gotchas with thinking models (Gemini 3.x, o-series): set RIDDLE_OPENAI_REASONING=low for faster first ink (some providers reject the field on non-thinking models — leave it unset there), and keep RIDDLE_OPENAI_MAX_TOKENS roomy — hidden reasoning tokens count against it, and a tight cap starves the visible reply.

Verify your setup before launching the diary:

riddle --oracle-test path/to/handwriting.png   # prints the streamed reply

Measured ~0.9–1.1 s to first ink on-device. The HTTPS is built into riddle (pure-Rust, no extra libraries).

Option B — pi (the power path)

If you already run pi, riddle will use a resident pi --mode rpc process kept warm (Node + your subscription auth loaded once), so each turn pays only model latency. Used automatically when RIDDLE_OPENAI_KEY is not set.

Both stream the reply sentence-by-sentence, so the quill starts writing seconds before the model finishes. The persona prompt lives in riddle/src/oracle.rs.

Building

Cross-compiled from x86_64. Two flavours:

Windowed (AppLoad/qtfb) — easiest

Requires xovi + AppLoad on the device.

cd riddle
cargo build --release --target aarch64-unknown-linux-gnu

Install to /home/root/xovi/exthome/appload/riddle/ with external.manifest.json, appload-launch.sh, and the binary.

Takeover (instant ink) — the one from the demo

Requires the reMarkable SDK toolchain (~/rm-sdk-3.26) because the linked vendor Qt libs need its glibc, and libqsgepaper.so pulled from your own device (it is proprietary and not distributed here):

cd quill && ./build.sh              # pulls libqsgepaper.so from the device over
                                    # ssh, builds libquill.so + the demos
cd ../riddle && ./build-takeover.sh
./scripts/make-bundle.sh            # stages the AppLoad bundle in dist/riddle/

The staged dist/riddle/ is self-contained (binary, libquill.so, launch scripts, manifest) — copy it to /home/root/xovi/exthome/appload/riddle/, or publish it to the catalog with remagic publish dist/riddle. Launching via AppLoad (appload-launch.sh) detaches into a transient systemd unit, stops xochitl, runs the diary, and always restores xochitl on exit — exit with the power button, a 5-finger tap, or SIGTERM. If anything wedges: ssh [email protected] 'systemctl start xochitl'.

Fonts

The reply hand is Dancing Script (SIL OFL 1.1 — see riddle/fonts/OFL.txt).

License

MIT for everything in this repository (see LICENSE). The vendor libraries it interposes (libqsgepaper.so, Qt) are not included and must come from your own device/SDK.