# ViewModels — index

MVVM layer. See [`schema.md`](../schema.md) for the memory-map conventions.

| File | Purpose |
|------|---------|
| `MainViewModel.cs` | The app brain: scenes/elements collections + commands, stream state (`IsLive`/`IsOffline`/`IsConnected`), chat feed, overlays, layout save/open, **resolution dropdown** (`QualityOptions`, `SelectedQuality`, `ResolutionHelp`, `ApplyStreamQuality`) that computes the output rect over the 1920×1080 master (`OutputRectX/Y/W/H`, `DimRects`, `IsOutputCropped`, `ResolutionBadgeText`). Auth: loads the saved DPAPI session at startup (`LoadSavedSessionAsync`), `SignInAsync` feeds the GoLive dialog; **End Livestream signs out** (`StopStream` clears session + token — crash-safe). **Webcam:** owns `CameraManager` (MediaCapture), `AddWebcamToActiveSceneAsync` (picker → default 480×270 bottom-right placement → acquire; the Windows camera picker ALWAYS opens so the creator chooses — never silently reuses the previous camera; picking a different camera swaps the app-wide identity via `SwapWebcamIdentityAsync`, same path as `ChangeWebcamAsync`; propagates the running shared bitmap via `CameraManager.GetPreviewBitmap` first, so a webcam added mid-session never renders a transparent container; greys out when the active scene already has a config via `CanAddWebcamToActiveScene`), `ChangeWebcamAsync` (device swap — `ReleaseAllAsync` old + re-acquire), `ShowWebcamInActiveScene` (reveal hidden config / empty-canvas right-click), `ReacquireWebcam` after layout load (re-propagates the shared bitmap to every config), `OnCameraPreviewBitmapChanged` forwards the shared bitmap into every `WebcamSceneConfig.VideoImageSource`; `SelectedElement` drives the preview overlay + `internal ClampWebcamToBounds(config, sceneName)` (per-scene size cap seam: 50%-per-dimension everywhere, half-screen-AREA in Chat via `MaxWebcamWidthFor`/`MaxWebcamHeightFor`). **Scenes (five-scene catalog):** empty DB seeds Starting/Live/BRB/Chat/Ending (`SceneCatalog.All`); `AddScene(name)` accepts only canonical, missing names; `MissingScenes`/`ShowAddScene` drive the "+" button (hidden once all five exist; its menu lists only the missing scenes via `AddSceneCommand`). **Screen backdrop (Live-only by policy):** owns `ScreenCaptureManager` + `ScreenCaptureSourceFactory` (WinRT GraphicsCapture), `internal static EnsureBackdrop` heals one per backdrop-enabled scene (gated on `Scene.HasBackdrop`), `ReacquireScreenCaptures`/`RefreshBackdropAutoCapture`/`NoteBackgroundWindow` key by full-screen game monitor or the **primary display** via `Win32FullScreenDetector` (`GetDisplays()`/`PrimaryMonitorIndex()`), `ChangeBackdropCaptureAsync` (OS picker) + `SetBackdropCapture(DisplayInfo)` (in-app "Capture Display"), `RedesignateBackdropAsync` re-targets all backdrops and releases orphaned sessions, `internal static EnforceBackdropPolicy` normalizes `Scene.HasBackdrop` by name on every load + strips lingering non-Live backdrops, `CanChangeBackdrop` gates the capture menu to Live (the only scene with a backdrop), `BackdropImage` hides the preview watermark (`ShowPreviewPlaceholder`) |
| `GoLiveViewModel.cs` | Start Stream dialog: **account row** (saved channel shown with Change Account, or Sign in to YouTube; Start gated on `IsSignedIn`/`IsBusy`) + title/description/visibility, start/cancel requests |
| `ReuseImageViewModel.cs` | Add Image dialog: candidate list (`ReuseImageCandidate`), reuse/new/cancel |
| `CameraPickerViewModel.cs` | Add Webcam dialog: async camera list (loading / has / none states), `UseRequested(CameraDeviceInfo)`/`CancelRequested` |

Related: [`Models/index.md`](../Models/index.md) for the data; [`Services/index.md`](../Services/index.md)
for what the ViewModels drive; base class in [`Helpers/ViewModelBase.cs`](../Helpers/ViewModelBase.cs).
