# Helpers — index

Cross-cutting utilities. See [`schema.md`](../schema.md) for the memory-map conventions.

| File | Purpose |
|------|---------|
| `ViewModelBase.cs` | `INotifyPropertyChanged` + `SetProperty<T>()` — base for all ViewModels |
| `RelayCommand.cs` | `ICommand` implementation for all button actions |
| `AppLog.cs` | File logger to `%APPDATA%\ytLlive\startup.log`; startup checkpoints + unhandled-exception capture (the crash this map is named for). Size-capped: rolls to `startup.1.log` at 5 MB (TASK 55) |
| `LogRotation.cs` | The size-capped-rotation policy as a pure function over a path: roll `startup.log` → `startup.1.log` when it passes the cap, keeping N rolled copies. Separate from `AppLog` so the logger's 156-call-site surface never changes and the rule is testable alone (TASK 55) |
| `FocusPreservingListBox.cs` | `ListBox` subclass that keeps selection/focus coherent when the selected item is deleted; `IsSelectable` predicate skips hidden scenes; drag-reorder guard |
| `OAuthCredentials.cs` | Baked-in Google OAuth client ID/secret (desktop app; loopback callback) |
| `TokenStore.cs` | DPAPI-protected OAuth session persistence (`%APPDATA%\ytLlive\ytLlive.auth`, CurrentUser scope); `Save`/`Load`/`Clear` — sign-in survives restarts |
| `ImageCache.cs` | Image byte caching (assets live in the DB) |
| `InverseBoolToVisibilityConverter.cs` / `NotNullToVisibilityConverter.cs` | XAML value converters for visibility bindings |
| `AllTrueToVisibilityConverter.cs` | Multi-value AND-gate → Visible; gates the layer-row capture menu items on row-IsBackground + staged-scene-is-Live (TASK 25) |
| `CameraConflictProbe.cs` | Best-effort diagnostic: when a camera won't start, enumerates running processes known to hold cameras (OBS, Zoom, Teams, NVIDIA Broadcast, browsers, etc.) — Windows doesn't expose "which process has this device" via any public API, so this is a suspect list, not a verdict |
| `StripPool.cs` | Four DEDICATED background threads at `BelowNormal` priority that split one composite into horizontal row strips (the caller runs a strip too); started lazily, runs inline below 64 rows. UNIT 5 — do NOT demote the ThreadPool from `Parallel.For`, it leaks into unrelated work (see [`docs/ai/frame-pipeline.md`](../docs/ai/frame-pipeline.md) → "Render budget") |
| `FrameCadence.cs` | Pure arrival-cadence counter (`FrameCadence` + `FrameCadenceSummary.Describe`): frames, gaps, hitches, longest/avg gap for a window of a timestamped stream. Fed by `MediaCaptureFrameSource` (camera stamps vs our arrivals) and `FramePump` (distinct webcam Epochs that reached the output) — UNIT 0, see [`docs/ai/frame-pipeline.md`](../docs/ai/frame-pipeline.md) → "Frame cadence" |
| `HexToBrushConverter.cs` | A "#RRGGBB" hex string → `SolidColorBrush` (transparent on bad input), so a template can paint a colour swatch straight from the palette. Registered in the theme as `HexToBrush` — the theme paints the colour, never the UI code (TASK 63) |
| `ClosedBoxTemplateSelector.cs` | An `ItemTemplateSelector` that gives a ComboBox's CLOSED box a different template from its drop-down rows: WPF calls it with the `ContentPresenter`'s templated parent — the `ComboBox` for the closed box, the `ComboBoxItem` for a row. The only way to tell them apart (`SelectionBoxItemTemplate` is read-only and mirrors `ItemTemplate`) — TASK 63 |

Related: [`Themes/Controls.xaml`](../Themes/Controls.xaml) styles the lists this
class backs; [`Models/index.md`](../Models/index.md) and
[`ViewModels/index.md`](../ViewModels/index.md) for the objects it works on.