Start the design document with the high-level architecture
DESIGN.md: one process with several threads (D16), three layers (D17), HA-centric object classes (D18), injected configuration (D19). Design decisions move from REQUIREMENTS.md to DESIGN.md. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Claude Opus 5.5
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# Design
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Status: **in progress**, iteration 1, phase 2 (planning and design). High-level architecture
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first, then the details for the MVP. Requirements and their decisions (D1–D15):
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[REQUIREMENTS.md](REQUIREMENTS.md). Design decisions start at D16.
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## Process and threads
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- **One process** started by SteamVR does everything: HA connection, sensors, services, all
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overlays (D16).
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- Several threads inside it for concurrent work. Which work runs in which thread is still open.
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## Layers
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Three layers; dependencies only go downward (D17).
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```
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Presentation QML (view and controller)
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▼
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Business logic entities, services, managers
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▼
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I/O HA connection (MQTT), SteamVR, system (network, audio)
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```
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- Qt Quick already enforces separating presentation from logic.
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- The overlay platform (`vrdashboard_core`) spans two layers: overlays, rendering and input
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are presentation infrastructure; SteamVR access for sensors and actions is I/O.
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## Object classes
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The app is HA-centric, so its building blocks follow HA's concepts (D18). Objects talk to each
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other through Qt signals and slots (Qt's observer pattern). Senders don't know their receivers,
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and signals across threads are delivered through the receiver's event loop.
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| Class | Role | MVP |
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|---|---|---|
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| **HA entity** | One HA entity, both directions. Entity → HA: state and JSON attributes. HA → entity: basic commands. Observes value signals of other objects and publishes them; turns MQTT commands into signals other objects act on. Covers sensors, simple actions (`button`), settings (`switch`, `number`), feedback (`event`). | ✓ |
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| **HA service** | An action HA calls with parameters: a JSON command on an MQTT command topic (HA side: the standard `mqtt.publish` action). May be more complex than an entity command. Results go back asynchronously, e.g. through an `event` entity. How the user wraps it in HA (scripts, automations, pyscript) is their choice; FrameAssistant only requires stock HA with MQTT (NFR-6). | ✓ (notification) |
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| **HA device** | Owns the MQTT connection, discovery and availability, and owns all entity and service objects. One per headset (CON-5). | ✓ |
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| **I/O wrappers** | Data sources and actuators; know nothing about HA. One wrapper object per OpenVR interface used (e.g. `IVRSystem`, `IVRApplications`, `IVRChaperone`, `IVRSettings`). System wrappers (network, audio) later. | OpenVR ✓, system ✗ |
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| **Overlays** | View and controller of MVC (QML), as dashboard tabs or world overlays. Get their data (the model) from other objects. | ✓ |
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| **Managers** | One object per stateful feature that manages and coordinates it, using entities, services and overlays. Notification manager (MVP); status card manager (SRV-6/7) later. | notifications ✓ |
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| **HA web UI** | Encapsulates Qt WebEngine for the dashboard (Q2). | ✗ |
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| **Configuration** | Settings from the JSON file, loaded once by the app as an immutable value. Each component gets the part it needs through its constructor (D19). | ✓ |
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| **App** | The managing object: owns all of the above as components and wires them together. | ✓ |
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Notes for later:
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- OpenVR delivers all events through one queue; one dispatcher (today `VrRuntime`) hands them
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to the wrappers.
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- OpenVR is not documented as thread-safe (relevant for the thread decision).
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## Open
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1. High-level points 3–7 (see [PROGRESS.md](PROGRESS.md), "Next steps").
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## Decisions
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| # | Date | Decision | Reason |
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|---|------|----------|--------|
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| D16 | 2026-10-05 | **One process** started by SteamVR does everything; several threads inside it for concurrent work | Meets NFR-2 without extra work, no IPC; the platform already supports several surfaces per process |
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| D17 | 2026-10-05 | **Three layers:** presentation (QML), business logic, I/O. The overlay platform spans presentation (overlays, rendering, input) and I/O (SteamVR access) | Simple and enough for the start; Qt Quick already enforces separating presentation from logic |
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| D18 | 2026-10-05 | **HA-centric object classes:** HA entity, HA service, HA device, I/O wrappers, overlays, managers, HA web UI, configuration, app; communication through signals and slots | The app is HA-centric; signals/slots decouple objects and work across threads |
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| D19 | 2026-10-05 | **Configuration is injected:** the app loads it once as an immutable value and passes each component the part it needs; no singleton | Explicit dependencies, trivial tests with own configs, thread-safe; the app creates all components anyway |
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+17
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@@ -10,21 +10,20 @@ CLAUDE.md ("Working rules").
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## Next steps
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Phase 2 for the MVP scope (D8: MQTT connection + discovery + availability, the MVP sensors, a
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basic notification). Design topics, proposed order:
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Phase 2: first the high-level architecture, then the details for the MVP (D8). High-level
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questions, in this order:
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1. ~~Q4: MQTT client library~~: done, libmosquitto (D14). Remaining for the design: Qt
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event-loop integration, shipping the library in the package (build + `install.sh`).
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2. Component structure: configuration, MQTT/discovery layer, sensor sources, notification
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service; how they fit into `Dashboard` (the app class).
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3. HA entity model: topics, discovery payloads, availability, device grouping (CON-2/3/5,
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SEN-15).
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4. Basic notification (NOT-1): needs an overlay outside the dashboard, i.e. the planned
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`WorldOverlay` (CLAUDE.md, "Planned extension"); MVP placement to be decided.
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5. Test strategy for the MVP and the measurement method for NFR-3.
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1. ~~Process model~~: one process, several threads (D16).
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2. ~~Layers~~: presentation, business logic, I/O (D17).
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3. How features plug in: object classes (D18) and configuration injection (D19) settled;
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open: how the classes are wired.
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4. HA channels: MQTT only, or prepare for a second one for the dashboard (Q2/Q3)?
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5. Overlay kinds: dashboard tabs and world overlays (platform extension).
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6. Runtime model: which work runs in which thread (D16: several threads).
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7. Test strategy at a high level.
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Later, not needed for the MVP: Q1 (several notifications), Q2/Q3 (dashboard); check only
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whether they constrain the MVP architecture.
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Details afterwards (MQTT library done: D14, D15): topics and payloads, basic notification,
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configuration, packaging of libmosquitto.
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## Log
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@@ -41,6 +40,11 @@ whether they constrain the MVP architecture.
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present (relevant for Q2/Q3).
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- libmosquitto ABI check: Debian's 2.0.21 needs at most `OPENSSL_3.0.0`/`GLIBC_2.34`; the
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Frame has OpenSSL 3.2.1 and glibc 2.39. No libcjson dependency. D14 holds.
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- Started docs/DESIGN.md: one process (D16), three layers (D17), HA-centric object classes
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(D18). HA side: FrameAssistant needs only stock HA; how the user wraps commands (scripts,
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pyscript) is up to them (NFR-6 unchanged).
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- Agreed to settle the high-level architecture first (list under "Next steps"), before
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component details.
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- Stay with the Debian build container: an Arch container wouldn't match SteamOS's own package
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versions (private repos, rolling Arch) and has no arm64 multiarch for cross builds.
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@@ -155,6 +155,8 @@ FrameAssistant.
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| D14 | 2026-10-05 | MQTT client: **libmosquitto** from Debian's package in the build container, shipped in the release package like `libopenvr_api.so` | Not on the Frame; Qt MQTT would need the exact Qt version (Appendix B) |
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| D15 | 2026-10-05 | HA MQTT discovery: **own small layer on Qt's JSON classes**, using device-based discovery (one `<prefix>/device/<id>/config` topic with all entities under `cmps`) | No suitable library (Appendix B); HA recommends device-based discovery for multi-entity devices (NFR-7) |
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Design decisions (D16 onward) are in [DESIGN.md](DESIGN.md).
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## Appendix A: data sources
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What the headset can report, by source. Checked against `openvr.h` (OpenVR 2.15.6). **None of
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