Implement first-class inking support (InkCanvas + InkToolBar)

[Nitin-100]

Implement First-Class Inking Support (InkCanvas + InkToolBar)

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Summary

This PR implements first-class inking support in WinUI 3 by expanding the InkCanvas API surface and replacing the InkToolBar E_NOTIMPL skeleton with a full working implementation. The changes follow the existing WinUI C++/WinRT patterns and integrate with the InkPresenter desktop infrastructure already in place.

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Changes

InkCanvas API Expansion

File	Change
src/controls/dev/InkCanvas/InkCanvas.idl	Added InkCanvasMode enum (Draw/Erase/Select), InkInputType flags enum (Pen/Touch/Mouse), InkCanvasStrokeCollectedEventArgs, InkCanvasStrokesErasedEventArgs runtime classes. Extended InkCanvas with Mode, AllowedInputTypes, DefaultDrawingAttributes properties, StrokeContainer accessor, SaveAsync/LoadAsync persistence methods, ClearStrokes, and StrokeCollected/StrokesErased events.
src/controls/dev/InkCanvas/InkCanvas.h	Added property changed callbacks (OnModePropertyChanged, OnAllowedInputTypesPropertyChanged, OnDefaultDrawingAttributesPropertyChanged), public StrokeContainer(), SaveAsync(), LoadAsync(), ClearStrokes() methods, and private helpers (UpdateInkPresenterMode, UpdateInkPresenterInputTypes, SetupStrokeEvents).
src/controls/dev/InkCanvas/InkCanvas.cpp	Implemented all new methods: mode switching maps to InkInputProcessingMode, input type filtering maps to CoreInputDeviceTypes, persistence uses InkStrokeContainer.SaveAsync/LoadAsync queued on the ink thread via task_completion_event, stroke events bridge InkPresenter.StrokesCollected/StrokesErased to the WinUI event surface.
src/controls/dev/InkCanvas/InkCanvasStrokeCollectedEventArgs.h	New file. Lightweight event args holding a single InkStroke.
src/controls/dev/InkCanvas/InkCanvasStrokesErasedEventArgs.h	New file. Lightweight event args holding an IVectorView<InkStroke>.
src/controls/dev/InkCanvas/InkCanvas.vcxitems	Added the two new event args headers to the build.

InkToolBar Implementation

File	Change
src/controls/dev/InkToolBar/InkToolBar.h	Replaced all E_NOTIMPL one-liners with proper method declarations. Added private state: tool button vectors, orientation, flyout placement, initial controls config, default-tools-created flag. Added OnApplyTemplate, CreateDefaultToolButtons, UpdateInkPresenterFromActiveTool, OnActiveToolChanged, OnTargetInkCanvasChanged, GetInkPresenter helpers.
src/controls/dev/InkToolBar/InkToolBar.cpp	New file (~280 lines). Full implementation: constructs default tool buttons (BallpointPen, Pencil, Highlighter, Eraser, Stencil) based on InitialControls, manages active tool state, synchronizes inking/erasing mode on the linked InkCanvas's InkPresenter, resolves presenter from either TargetInkCanvas or explicit TargetInkPresenter.
src/controls/dev/InkToolBar/InkToolBar.vcxitems	Added InkToolBar.cpp and all existing subclass headers (BallpointPenButton, PencilButton, HighlighterButton, EraserButton, StencilButton, CustomPen, toggles, menus, flyout items, automation peers, trace).

Build & Feature Flags

File	Change
src/controls/FeatureAreas.props	FeatureInkToolBarEnabled: false → true
src/controls/dev/Generated/InkCanvas.properties.h	Added AllowedInputTypes, DefaultDrawingAttributes, Mode dependency properties, StrokeCollected/StrokesErased event sources.
src/controls/dev/Generated/InkCanvas.properties.cpp	Registered the three new dependency properties with correct defaults and change callbacks. Added event source add/remove implementations.
src/controls/dev/Generated/InkToolBarMenuButton.properties.h/.cpp	Removed MenuKind dependency property (provided by base class, was duplicated).
src/controls/dev/dll/XamlMetadataProviderGenerated.h	Added XAML metadata entries for new InkCanvas properties/methods and InkToolBar types, enabling XAML tooling and runtime reflection.

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New API Surface

enum InkCanvasMode { Draw, Erase, Select };

[flags] enum InkInputType { None, Pen, Touch, Mouse };

runtimeclass InkCanvasStrokeCollectedEventArgs {
    Windows.UI.Input.Inking.InkStroke Stroke { get; };
};

runtimeclass InkCanvasStrokesErasedEventArgs {
    IVectorView<InkStroke> Strokes { get; };
};

unsealed runtimeclass InkCanvas : FrameworkElement {
    // Existing
    Boolean IsEnabled { get; set; };
    IAsyncAction QueueInkPresenterWorkItem(DoInkPresenterWork workItem);

    // New
    InkCanvasMode Mode { get; set; };                          // Default: Draw
    InkInputType AllowedInputTypes { get; set; };              // Default: Pen | Mouse
    InkDrawingAttributes DefaultDrawingAttributes { get; set; };
    InkStrokeContainer StrokeContainer { get; };               // Read-only access

    IAsyncAction SaveAsync(IOutputStream stream);
    IAsyncAction LoadAsync(IInputStream stream);
    void ClearStrokes();

    event TypedEventHandler<InkCanvas, InkCanvasStrokeCollectedEventArgs> StrokeCollected;
    event TypedEventHandler<InkCanvas, InkCanvasStrokesErasedEventArgs> StrokesErased;
};

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Design Decisions

1. Ink thread safety: All InkPresenter interactions are queued via QueueInkPresenterWorkItem / GenericInkCallback, following the existing pattern. SaveAsync and LoadAsync use task_completion_event to bridge async work across threads.

2. Event bridging: Stroke events subscribe to InkPresenter.StrokesCollected/StrokesErased (which fire on the ink thread) and re-raise through the generated event_source on the UI thread.

3. InkToolBar integration: InkToolBar resolves the InkPresenter via winrt::get_self<InkCanvas>()->InkPresenter() when TargetInkCanvas is set, or falls back to TargetInkPresenter for advanced scenarios.

4. Feature flag: FeatureInkToolBarEnabled is flipped to true. InkCanvas was already enabled.

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Testing

Full test infrastructure following the repo's standard 3-layer pattern (APITests, TestUI, InteractionTests) for both controls, registered in MUXControlsTestApp.csproj and MUXControls.Test.csproj with feature flag gating.

InkCanvas Tests (23 tests)

APITests (InkCanvas/APITests/InkCanvasTests.cs) — 17 unit tests:

• Default property values (IsEnabled, Mode, AllowedInputTypes)
• Mode property cycling (Draw → Erase → Select → Draw)
• AllowedInputTypes flags (Pen, Touch, Mouse, combined, None)
• IsEnabled toggle
• DefaultDrawingAttributes set/get (color, size, pen tip)
• StrokeContainer accessor safety (pre-load)
• ClearStrokes safety (pre-load)
• StrokeCollected / StrokesErased event subscription
• DependencyProperty access (ModeProperty, AllowedInputTypesProperty, DefaultDrawingAttributesProperty, IsEnabledProperty)
• XAML visual tree integration (with and without property binding)
• Multiple instance independence

TestUI (InkCanvas/TestUI/InkCanvasPage.xaml/.cs):

• Interactive test page with [TopLevelTestPage(Name = "InkCanvas")]
• Mode selector (Draw/Erase/Select), input type checkboxes (Pen/Mouse/Touch)
• Save/Load/Clear buttons with status display
• Live stroke count from StrokeContainer
• StrokeCollected / StrokesErased event handlers

InteractionTests (InkCanvas/InteractionTests/InkCanvasTests.cs) — 6 integration tests:

• Visual tree presence
• Mode switching via ComboBox
• Input type configuration via CheckBoxes
• Clear strokes button
• Save/Load round-trip
• Stroke count display

InkToolBar Tests (31 tests)

APITests (InkToolBar/APITests/InkToolBarTests.cs) — 24 unit tests:

• Default constructor
• InitialControls property (All/None/PensOnly/AllExceptPens)
• Children collection access
• Orientation property (Horizontal/Vertical)
• ButtonFlyoutPlacement property (Auto/Top/Bottom/Left/Right)
• IsRulerButtonChecked / IsStencilButtonChecked toggle
• TargetInkCanvas binding and clearing
• TargetInkPresenter binding
• ActiveTool / InkDrawingAttributes access
• GetToolButton / GetToggleButton / GetMenuButton lookup
• All 10 DependencyProperties existence check
• ActiveToolChanged / InkDrawingAttributesChanged / EraseAllClicked event subscription
• XAML visual tree (standalone and with linked InkCanvas)
• Multiple instance independence
• Subclass construction: InkToolBarBallpointPenButton, InkToolBarPencilButton, InkToolBarHighlighterButton, InkToolBarCustomToolButton, InkToolBarCustomToggleButton, InkToolBarStencilButton, InkToolBarFlyoutItem, InkToolBarPenConfigurationControl

TestUI (InkToolBar/TestUI/InkToolBarPage.xaml/.cs):

• Interactive test page with [TopLevelTestPage(Name = "InkToolBar")]
• InitialControls/Orientation/FlyoutPlacement selectors
• Ruler/Stencil toggle checkboxes
• Linked InkCanvas via TargetInkCanvas binding
• Active tool and event status display

InteractionTests (InkToolBar/InteractionTests/InkToolBarTests.cs) — 7 integration tests:

• Visual tree presence (toolbar + linked canvas)
• InitialControls selection cycling
• Orientation switching
• Flyout placement switching
• Ruler toggle
• Stencil toggle
• Active tool display

Standalone Validation App

A separate WinUI 3 test application (InkingTestApp) was built outside the repo to validate the Windows.UI.Input.Inking data model APIs:

• 16 automated tests covering InkStrokeBuilder, InkStrokeContainer, InkDrawingAttributes, serialization round-trip, and attribute fidelity
• Manual drawing tests: pointer-based canvas, erasing, tool switching, color/width selection
• Persistence tests: InMemoryRandomAccessStream save/load with visual verification

All 16 tests pass. Not included in this PR.

[riverar]

This probably isn't going to land in WinUI directly due to breaking API/etc. A better approach would be to submit this as a control to the Windows Community Toolkit, where it can get community feedback, be iterated on, and potentially/eventually get promoted into the core library if needed.