# Figment Mode Design Spec

> Periodic full-screen SVG glyph overlay with flickery animation, theme-aware coloring, and extensible physical device control.

## Overview

Figment mode displays a randomly selected SVG from the `figments/` directory as a flickery, glitchy half-block terminal overlay on top of the running ticker. It appears once per minute (configurable), holds for ~4.5 seconds with a three-phase animation (progressive reveal, strobing hold, dissolve), then fades back to the ticker. Colors are randomly chosen from the existing theme gradients.

The feature is designed for extensibility: a generic input protocol allows MQTT, ntfy, serial, or any other control surface to trigger figments and adjust parameters in real time.

## Goals

- Display SVG figments as half-block terminal art overlaid on the running ticker
- Three-phase animation: progressive reveal, strobing hold, dissolve
- Random color from existing theme gradients (green, orange, purple)
- Configurable interval and duration via C&C
- Extensible input abstraction for physical device control (MQTT, serial, etc.)

## Out of Scope

- Multi-figment simultaneous display (one at a time)
- SVG animation support (static SVGs only; animation comes from the overlay phases)
- Custom color palettes beyond existing themes
- MQTT and serial adapters (v1 ships with ntfy C&C only; protocol is ready for future adapters)

## Architecture: Hybrid Plugin + Overlay

The figment is an **EffectPlugin** for lifecycle, discovery, and configuration, but delegates rendering to a **layers-style overlay helper**. This avoids stretching the `EffectPlugin.process()` contract (which transforms line buffers) while still benefiting from the plugin system for C&C, auto-discovery, and config management.

**Important**: The plugin class is named `FigmentEffect` (not `FigmentPlugin`) to match the `*Effect` naming convention required by `discover_plugins()` in `effects_plugins/__init__.py`. The plugin is **not** added to the `EffectChain` order list — its `process()` is a no-op that returns the buffer unchanged. The chain only processes effects that transform buffers (noise, fade, glitch, firehose). Figment's rendering happens via the overlay path in `scroll.py`, outside the chain.

### Component Diagram

```
                     +-------------------+
                     |  FigmentTrigger   |  (Protocol)
                     |  - NtfyTrigger    |  (v1)
                     |  - MqttTrigger    |  (future)
                     |  - SerialTrigger  |  (future)
                     +--------+----------+
                              |
                              | FigmentCommand
                              v
+------------------+    +-----------------+    +----------------------+
| figment_render   |<---| FigmentEffect   |--->| render_figment_      |
| .py              |    | (EffectPlugin)  |    | overlay() in         |
|                  |    |                 |    | layers.py            |
| SVG -> PIL ->    |    | Timer, state    |    |                      |
| half-block cache |    | machine, SVG    |    | ANSI cursor-position |
|                  |    | selection       |    | commands for overlay |
+------------------+    +-----------------+    +----------------------+
                              |
                              | get_figment_state()
                              v
                     +-------------------+
                     | scroll.py         |
                     +-------------------+
```

## Section 1: SVG Rasterization

**File: `engine/figment_render.py`**

Reuses the same PIL-based half-block encoding that `engine/render.py` uses for OTF fonts.

### Pipeline

1. **Load**: `cairosvg.svg2png()` converts SVG to PNG bytes in memory (no temp files)
2. **Resize**: PIL scales to fit terminal — width = `tw()`, height = `th() * 2` pixels (each terminal row encodes 2 pixel rows via half-blocks)
3. **Threshold**: Convert to greyscale ("L" mode), apply binary threshold to get visible/not-visible
4. **Half-block encode**: Walk pixel pairs top-to-bottom. For each 2-row pair, emit `█` (both lit), `▀` (top only), `▄` (bottom only), or space (neither)
5. **Cache**: Results cached per `(svg_path, terminal_width, terminal_height)` — invalidated on terminal resize

### Dependency

`cairosvg` added as an optional dependency in `pyproject.toml` (like `sounddevice`). If `cairosvg` is not installed, the `FigmentEffect` class will fail to import, and `discover_plugins()` will silently skip it (the existing `except Exception: pass` in discovery handles this). The plugin simply won't appear in the registry.

### Key Function

```python
def rasterize_svg(svg_path: str, width: int, height: int) -> list[str]:
    """Convert SVG file to list of half-block terminal rows (uncolored)."""
```

## Section 2: Figment Overlay Rendering

**Integration point: `engine/layers.py`**

New function following the `render_message_overlay()` pattern.

### FigmentState Dataclass

Defined in `effects_plugins/figment.py`, passed between the plugin and the overlay renderer:

```python
@dataclass
class FigmentState:
    phase: FigmentPhase          # enum: REVEAL, HOLD, DISSOLVE
    progress: float              # 0.0 to 1.0 within current phase
    rows: list[str]              # rasterized half-block rows (uncolored)
    gradient: list[int]          # 12-color ANSI 256 gradient from chosen theme
    center_row: int              # top row for centering in viewport
    center_col: int              # left column for centering in viewport
```

### Function Signature

```python
def render_figment_overlay(figment_state: FigmentState, w: int, h: int) -> list[str]:
    """Return ANSI cursor-positioning commands for the current figment frame."""
```

### Animation Phases (~4.5 seconds total)

Progress advances each frame as: `progress += config.FRAME_DT / phase_duration`. At 20 FPS (FRAME_DT=0.05s), a 1.5s phase takes 30 frames to complete.

| Phase | Duration | Behavior |
|-------|----------|----------|
| **Reveal** | ~1.5s | Progressive scanline fill. Each frame, a percentage of the figment's non-empty cells become visible in random block order. Intensity scales reveal speed. |
| **Hold** | ~1.5s | Full figment visible. Strobes between full brightness and dimmed/partial visibility every few frames. Intensity scales strobe frequency. |
| **Dissolve** | ~1.5s | Inverse of reveal. Cells randomly drop out, replaced by spaces. Intensity scales dissolve speed. |

### Color

A random theme gradient is selected from `THEME_REGISTRY` at trigger time. Applied via `lr_gradient()` — the same function that colors headlines and messages.

### Positioning

Figment is centered in the viewport. Each visible row is an ANSI `\033[row;colH` command appended to the buffer, identical to how the message overlay works.

## Section 3: FigmentEffect (Effect Plugin)

**File: `effects_plugins/figment.py`**

An `EffectPlugin(ABC)` subclass named `FigmentEffect` to match the `*Effect` discovery convention.

### Chain Exclusion

`FigmentEffect` is registered in the `EffectRegistry` (for C&C access and config management) but is **not** added to the `EffectChain` order list. Its `process()` returns the buffer unchanged. The `enabled` flag is checked directly by `scroll.py` when deciding whether to call `get_figment_state()`, not by the chain.

### Responsibilities

- **Timer**: Tracks elapsed time via `config.FRAME_DT` accumulation. At the configured interval (default 60s), triggers a new figment.
- **SVG selection**: Randomly picks from `figments/*.svg`. Avoids repeating the last shown.
- **State machine**: `idle -> reveal -> hold -> dissolve -> idle`. Tracks phase progress (0.0 to 1.0).
- **Color selection**: Picks a random theme key (`"green"`, `"orange"`, `"purple"`) at trigger time.
- **Rasterization**: Calls `rasterize_svg()` on trigger, caches result for the display duration.

### State Machine

```
idle ──(timer fires or trigger received)──> reveal
reveal ──(progress >= 1.0)──> hold
hold ──(progress >= 1.0)──> dissolve
dissolve ──(progress >= 1.0)──> idle
```

### Interface

The `process()` method returns the buffer unchanged (no-op). The plugin exposes state via:

```python
def get_figment_state(self, frame_number: int) -> FigmentState | None:
    """Tick the state machine and return current state, or None if idle."""
```

This mirrors the `ntfy_poller.get_active_message()` pattern.

### Scroll Loop Access

`scroll.py` imports `FigmentEffect` directly and uses `isinstance()` to safely downcast from the registry:

```python
from effects_plugins.figment import FigmentEffect

plugin = registry.get("figment")
figment = plugin if isinstance(plugin, FigmentEffect) else None
```

This is a one-time setup check, not per-frame. If `cairosvg` is missing, the import is wrapped in a try/except and `figment` stays `None`.

### EffectConfig

- `enabled`: bool (default `False` — opt-in)
- `intensity`: float — scales strobe frequency and reveal/dissolve speed
- `params`:
  - `interval_secs`: 60 (time between figments)
  - `display_secs`: 4.5 (total animation duration)
  - `figment_dir`: "figments" (SVG source directory)

Controllable via C&C: `/effects figment on`, `/effects figment intensity 0.7`.

## Section 4: Input Abstraction (FigmentTrigger)

**File: `engine/figment_trigger.py`**

### Protocol

```python
class FigmentTrigger(Protocol):
    def poll(self) -> FigmentCommand | None: ...
```

### FigmentCommand

```python
class FigmentAction(Enum):
    TRIGGER = "trigger"
    SET_INTENSITY = "set_intensity"
    SET_INTERVAL = "set_interval"
    SET_COLOR = "set_color"
    STOP = "stop"

@dataclass
class FigmentCommand:
    action: FigmentAction
    value: float | str | None = None
```

Uses an enum for consistency with `EventType` in `engine/events.py`.

### Adapters

| Adapter | Transport | Dependency | Status |
|---------|-----------|------------|--------|
| `NtfyTrigger` | Existing C&C ntfy topic | None (reuses ntfy) | v1 |
| `MqttTrigger` | MQTT broker | `paho-mqtt` (optional) | Future |
| `SerialTrigger` | USB serial | `pyserial` (optional) | Future |

**NtfyTrigger v1**: Subscribes as a callback on the existing `NtfyPoller`. Parses messages with a `/figment` prefix (e.g., `/figment trigger`, `/figment intensity 0.8`). This is separate from the `/effects figment on` C&C path — the trigger protocol allows external devices to send commands without knowing the effects controller API.

### Integration

The `FigmentEffect` accepts a list of triggers. Each frame, it polls all triggers and acts on commands. Triggers are optional — if none are configured, the plugin runs on its internal timer alone.

### EventBus Bridge

A new `FIGMENT_TRIGGER` variant is added to the `EventType` enum in `engine/events.py`, with a corresponding `FigmentTriggerEvent` dataclass. Triggers publish to the EventBus for other components to react (logging, multi-display sync).

## Section 5: Scroll Loop Integration

Minimal change to `engine/scroll.py`:

```python
# In stream() setup (with safe import):
try:
    from effects_plugins.figment import FigmentEffect
    _plugin = registry.get("figment")
    figment = _plugin if isinstance(_plugin, FigmentEffect) else None
except ImportError:
    figment = None

# In frame loop, after effects processing, before ntfy message overlay:
if figment and figment.config.enabled:
    figment_state = figment.get_figment_state(frame_number)
    if figment_state is not None:
        figment_overlay = render_figment_overlay(figment_state, w, h)
        buf.extend(figment_overlay)
```

### Overlay Priority

Figment overlay appends **after** effects processing but **before** the ntfy message overlay. This means:
- Ntfy messages always appear on top of figments (higher priority)
- Existing glitch/noise effects run over the ticker underneath the figment

Note: If more overlay types are added in the future, a priority-based overlay system should replace the current positional ordering.

## Section 6: Error Handling

| Scenario | Behavior |
|----------|----------|
| `cairosvg` not installed | `FigmentEffect` fails to import; `discover_plugins()` silently skips it; `scroll.py` import guard sets `figment = None` |
| `figments/` directory missing | Plugin logs warning at startup, stays in permanent `idle` state |
| `figments/` contains zero `.svg` files | Same as above: warning, permanent `idle` |
| Malformed SVG | `cairosvg` raises exception; plugin catches it, skips that SVG, picks another. If all SVGs fail, enters permanent `idle` with warning |
| Terminal resize during animation | Re-rasterize on next frame using new dimensions. Cache miss triggers fresh rasterization. Animation phase/progress are preserved; only the rendered rows update |

## Section 7: File Summary

### New Files

| File | Purpose |
|------|---------|
| `effects_plugins/figment.py` | FigmentEffect — lifecycle, timer, state machine, SVG selection, FigmentState/FigmentPhase |
| `engine/figment_render.py` | SVG to half-block rasterization pipeline |
| `engine/figment_trigger.py` | FigmentTrigger protocol, FigmentAction enum, FigmentCommand, NtfyTrigger adapter |
| `figments/` | SVG source directory (ships with sample SVGs) |
| `tests/test_figment.py` | FigmentEffect lifecycle, state machine transitions, timer |
| `tests/test_figment_render.py` | SVG rasterization, caching, edge cases |
| `tests/test_figment_trigger.py` | FigmentCommand parsing, NtfyTrigger adapter |
| `tests/fixtures/test.svg` | Minimal SVG for deterministic rasterization tests |

### Modified Files

| File | Change |
|------|--------|
| `engine/scroll.py` | Figment overlay integration (setup + per-frame block) |
| `engine/layers.py` | Add `render_figment_overlay()` function |
| `engine/events.py` | Add `FIGMENT_TRIGGER` to `EventType` enum, add `FigmentTriggerEvent` dataclass |
| `pyproject.toml` | Add `cairosvg` as optional dependency |

## Testing Strategy

- **Unit**: State machine transitions (idle→reveal→hold→dissolve→idle), timer accuracy (fires at interval_secs), SVG rasterization output dimensions, FigmentCommand parsing, FigmentAction enum coverage
- **Integration**: Plugin discovery (verify `FigmentEffect` is found by `discover_plugins()`), overlay rendering with mock terminal dimensions, C&C command handling via `/effects figment on`
- **Edge cases**: Missing figments dir, empty dir, malformed SVG, cairosvg unavailable, terminal resize mid-animation
- **Fixture**: Minimal `test.svg` (simple rectangle) for deterministic rasterization tests