99 lines
6.4 KiB
Markdown
99 lines
6.4 KiB
Markdown
# Architecture
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## Overview
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The program rotates a pan gimbal carrying up to four cameras, periodically stops/points it, triggers the
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cameras, compresses frames to JPEG XL, writes them to disk, and announces each capture over MQTT. Remote
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operators can override behaviour over MQTT.
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The design separates **policy** (the control logic) from **mechanism** (the I/O to hardware/broker):
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- **`fgc_core`** — an SDK-independent static library: typed configuration, path resolution, logging, the
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telemetry/command parsers, and the `CaptureScheduler` (control state machine). Depends on nothing
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proprietary, so it builds and unit-tests anywhere.
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- **Three interfaces** abstract the outside world, each with a real and a mock/null implementation:
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| Interface | Real | Mock / Null |
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|-----------|------|-------------|
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| `IMotorController` | `SerialMotorController` (Boost.Asio) | `MockMotorController` (simulated sweep) |
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| `IControlChannel` | `MqttControlChannel` (Paho) | `NullControlChannel` (no broker) |
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| `ICameraSource` | `VimbaCameraSource` (Vimba X) | `MockCameraSource` (synthetic frames) |
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`Application` picks real vs mock from config + CLI, wires everything to the `ImagePipeline` and
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`CaptureScheduler`, and runs the loop. Selecting mocks lets the whole system run with **no hardware or broker**.
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```
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┌──────────────── fgc_core (no SDKs) ───────────────┐
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main.cpp ──► Application ──► CaptureScheduler ──► (interfaces below) │
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│ Config · Logger · Paths · TelemetryParser · CommandParser│
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└───────────────────────────────────────────────────────────┘
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│ builds + owns
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┌────────────────┼───────────────────────────┬──────────────────────┐
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IMotorController IControlChannel ICameraSource ImagePipeline
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Serial/Mock Mqtt/Null Vimba/Mock ◄── frames ──┘ encode→.jxl→CamEvent
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│ │ │
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serial MQTT broker cameras
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```
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## Threading model
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| Thread | Where | Role |
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|--------|-------|------|
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| Main / control loop | `Application::run` | 10 ms tick: drain UI commands, `scheduler.tick()`, publish a `UiSnapshot` |
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| UI input (headless) | `HeadlessUi` | reads stdin lines into the command sink |
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| UI render + input (TUI) | `TuiUi` | FTXUI event loop + 10 Hz refresher; pulls snapshots, pushes commands |
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| Serial I/O | `SerialMotorController` | Boost.Asio `io_context`; async read-until parses telemetry |
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| Image worker | `ImagePipeline` | drains the frame queue: rotate → encode → write → publish |
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| MQTT client | Paho (internal) | delivers callbacks; auto-reconnects (no busy-wait loop) |
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| Camera acquisition | Vimba X (internal) | delivers frames via the observer (real source) |
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Shared state is mutex-guarded: latest `MotorTelemetry` (serial), `ControlCommand` (channel), the frame queue
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(pipeline), the console command queue, and the latest `UiSnapshot`. The `CaptureScheduler` runs only on the
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main thread; the UI is a pure observer + command source (it copies a snapshot to render and pushes command
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strings back through the same queue the console uses, so it never touches live logic objects). In TUI mode
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all `Logger` output is diverted to an on-screen pane via a `Logger::setSink` callback so the screen is never
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corrupted.
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## Data flow
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1. **Startup** — `main()` parses CLI, resolves + loads config, constructs `Application`, which builds the
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motor/channel/camera (real or mock), the `ImagePipeline`, and the `CaptureScheduler`.
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2. **Telemetry** — the real motor controller streams firmware `ST Y:...[ P:...]` lines; `parseTelemetryLine`
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turns each into a per-axis `MotorTelemetry` snapshot (state + encoder counts + flags). The mock synthesizes
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one. Encoder counts are mapped to/from degrees by `Geometry` (`[Motor]` calibration).
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3. **Control input** — `IControlChannel::poll()` returns the latest `ControlCommand` (control code + target
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heading), clearing its "available" flags so each update is acted on once.
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4. **Capture cycle** (`CaptureScheduler::tick`, per 10 ms) — a move → settle → trigger machine:
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- ControlCode 0: `MOVE <yaw>,<pitch>` to the next `ScanGrid` waypoint (ping-pong).
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- ControlCode 1: `MOVE` yaw to `target_HDG` (pitch held), converted to counts via `Geometry`.
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- Trigger the cameras once **both axes report standstill at the target**, then advance the grid.
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5. **Frame handling** — a triggered camera delivers a `Frame` to the callback, which `submit()`s it to the
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`ImagePipeline`. The worker rotates it 90° CCW, encodes JPEG XL (or copies the demo image), writes
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`<output_dir>/<label>/<unix_ms>.jxl`, and publishes a `CamEvent` (yaw + pitch from the encoders).
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## Capture state machine
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```
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interval elapsed AND capture active AND not already moving
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│
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▼
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┌──────────────────────┐ ControlCode 0 → next ScanGrid (yaw,pitch)
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│ MOVE <yaw>,<pitch> │ ControlCode 1 → target_HDG (pitch held)
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└──────────┬───────────┘ deg→counts via Geometry; set moving, reset timer
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│ (both axes standstill AND |xenc − target| ≤ tol)
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▼
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┌──────────────────────┐
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│ camera.trigger() │ on success: clear moving, advance grid (ControlCode 0)
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└──────────────────────┘
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```
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Triggering only at the settled target replaces the original's trigger-while-moving behaviour (see
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[known-issues.md](known-issues.md) #7). The scheduler is unit-tested with mock doubles and an injected clock
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([tests/test_scheduler.cpp](../tests/test_scheduler.cpp)).
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## Why this shape
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Decoupling the control logic from the SDKs makes the core testable and the binary buildable/runnable without
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proprietary dependencies, while preserving the original real-time behaviour. Persistence remains deliberately
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limited to image files plus fire-and-forget MQTT.
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