Add ReorderableTree, a drag-reorderable tree of caller-drawn rows

CLAUDE.md

@@ -28,7 +28,7 @@ This is the **ktsu ImGui Suite**, a collection of .NET libraries for building De
 ### Libraries
 
 - **ImGui.App** (`ktsu.ImGui.App`) - Application foundation with windowing, rendering, font/texture management, PID frame limiting, DPI awareness. Image decoding is self-contained (`ImGui.App/Images/`), so the package carries no imaging dependency; see [Image decoding](#image-decoding) below.
-- **ImGui.Widgets** (`ktsu.ImGui.Widgets`) - Custom UI components, grouped as the README's feature list groups them: input and controls (`Switch`, `SegmentedControl`, `Stepper`, `TimecodeField` over the ImGui-free `Timecode`/`TimecodeRate`, `RangeSlider`, `ChannelFader`/`FaderTaper`, `XYPad`, `ColorWheel`/`LiftGammaGain`, `Knob`/`KnobWithDrag`, `Rating`, `Chip`/`ChipGroup`, `PinInput`, `SearchBox`/`SearchBoxRanked`, `Combo`, `StepGrid`, `PianoKeyboard` over a caller-owned `PianoKeyboardLayout`, `TransportScrubber`); display and status (`Avatar`, `Badge`/`BadgeDot`, `ColorIndicator`, `Icon`, `Text`, `Image`, `PageIndicator`); progress and loading (`RadialProgressBar` with `RadialCountdown`/`RadialCountUp`, `SkeletonLine`/`SkeletonRect`/`SkeletonCircle`); data and signals (`Histogram`, `FrameTimeGraph` over a caller-owned `FrameTimeHistory`, `HandleTrack`, `CurveTrack`, `DbMeter`, `GainReductionMeter`, `CorrelationMeter`/`StereoMetersState`, `Goniometer`, `Scope`, `Waveform` (zoomable over a caller-owned `TimelineView` and a `WaveformPeakSource`/`WaveformPeakCache`), `SpectrumAnalyzer` over a caller-owned `SpectrumAnalyzerState`, `EnvelopeEditor` over an `Envelope`, `ParametricEq` over `EqBand`s with `EqResponse` for the RBJ biquad response, and image and colour (`LevelsControl` over a caller-owned `LevelsAdjustment`, `AssetBrowser` over a caller-owned `AssetBrowserState`, whose `Apply` is the transfer function the widget draws, `GradientEditor` over a caller-owned list of `GradientStop`, with `SampleGradient` as the evaluator the bar `Toolbar`/`ToolbarSeparator` with `ToolbarButton`/`ToolbarToggleButton` (glyph and label in one frame, `ToolbarButtonLayout` picking leading, above-and-centred, glyph-only or label-only, the arithmetic in the ImGui-free `ToolbarGeometry`; `GlyphSize` on the toolbar or a button draws icons at their own pixel size beside normal-size labels), is drawn with, `SwatchPalette`, `ImageCompare`, `CropOverlay` over an `ImageCanvas`, `PixelLoupe` beside an `ImageCanvas`); the `LogFrequencyAxis` both share); layout and containers (`DividerContainer`/`DividerZone`, `Grid`, `TabPanel`, `Card`, `Tree`, `ImageCanvas`, `PropertyGrid`, `OverlayHost`/`OverlayLayer`, `ScopedDisable`, `ScopedId`); and motion and gestures (`Tween`, `Spring`, `Easing`, `InertialScroll`, `GestureDetector`/`GestureMachine`). Also thin adapters delegating to `Hexa.NET.ImGui.Widgets`: `Spinner`, `BufferingBar`, `HorizontalSplitter`/`VerticalSplitter`, `ToggleSwitch`/`ToggleButton`/`TransparentButton`/`InlineButton`, `IconTreeNode`, `EnumCombo`, `TextCenteredV`/`TextCenteredH`/`TextCenteredVH`, `ImageCenteredV`/`ImageCenteredH`/`ImageCenteredVH`/`ImageScaleTo`, `Tooltip`, `Breadcrumb`, `DatePicker`/`YearPicker`, `FlameGraph`, `FileTreeView`, `OpenFileDialog`/`SaveFileDialog`/`OpenFolderDialog`, `RenameDialog`, `DialogMessageBox`/`ShowMessageBox`, `DockedWindow`. Seven of these look like duplicates of an existing ktsu widget; most are not, and the two that are have a recommended survivor — see [Hexa-backed vs ktsu widgets](#hexa-backed-vs-ktsu-widgets) below for the pair-by-pair verdict. `DatePicker` and `FileTreeView` need a Material Icons font registered via `FontHelper.AddCustomFont(io, data, size, FontHelper.GetMaterialIconRanges(), mergeWithPrevious: true)` (not `ImGuiAppConfig.Fonts`, which applies the Nerd Font mapping); see `examples/ImGuiAppDemo`. `YearPicker` needs no icon font. `OpenFileDialog`, `SaveFileDialog` and `OpenFolderDialog` need the same Material Icons font, for their toolbar, breadcrumb and file-tree glyphs; `RenameDialog`, `DialogMessageBox` and `ShowMessageBox` need none. `DockedWindow` composes Hexa's `ImWindow` internally rather than inheriting it — subclass it, override `Title` and `DrawContent()`, then call `Show()`/`Close()`. All of the dialogs and `DockedWindow` require a per-frame deferred-drawing pump; see [Deferred Drawing](#deferred-drawing-dialogs-and-docked-windows) below. Also includes callback-driven editors: `Sequencer`, `SequenceSource`, `CurveEditor`, `CurveSource`, `CurveData`, `BezierEditor`. Unlike the dialogs above, none of these need a deferred-drawing pump; see [Callback-driven editors](#callback-driven-editors) below.
+- **ImGui.Widgets** (`ktsu.ImGui.Widgets`) - Custom UI components, grouped as the README's feature list groups them: input and controls (`Switch`, `SegmentedControl`, `Stepper`, `TimecodeField` over the ImGui-free `Timecode`/`TimecodeRate`, `RangeSlider`, `ChannelFader`/`FaderTaper`, `XYPad`, `ColorWheel`/`LiftGammaGain`, `Knob`/`KnobWithDrag`, `Rating`, `Chip`/`ChipGroup`, `PinInput`, `SearchBox`/`SearchBoxRanked`, `Combo`, `StepGrid`, `PianoKeyboard` over a caller-owned `PianoKeyboardLayout`, `TransportScrubber`); display and status (`Avatar`, `Badge`/`BadgeDot`, `ColorIndicator`, `Icon`, `Text`, `Image`, `PageIndicator`); progress and loading (`RadialProgressBar` with `RadialCountdown`/`RadialCountUp`, `SkeletonLine`/`SkeletonRect`/`SkeletonCircle`); data and signals (`Histogram`, `FrameTimeGraph` over a caller-owned `FrameTimeHistory`, `HandleTrack`, `CurveTrack`, `DbMeter`, `GainReductionMeter`, `CorrelationMeter`/`StereoMetersState`, `Goniometer`, `Scope`, `Waveform` (zoomable over a caller-owned `TimelineView` and a `WaveformPeakSource`/`WaveformPeakCache`), `SpectrumAnalyzer` over a caller-owned `SpectrumAnalyzerState`, `EnvelopeEditor` over an `Envelope`, `ParametricEq` over `EqBand`s with `EqResponse` for the RBJ biquad response, and image and colour (`LevelsControl` over a caller-owned `LevelsAdjustment`, `AssetBrowser` over a caller-owned `AssetBrowserState`, whose `Apply` is the transfer function the widget draws, `GradientEditor` over a caller-owned list of `GradientStop`, with `SampleGradient` as the evaluator the bar `Toolbar`/`ToolbarSeparator` with `ToolbarButton`/`ToolbarToggleButton` (glyph and label in one frame, `ToolbarButtonLayout` picking leading, above-and-centred, glyph-only or label-only, the arithmetic in the ImGui-free `ToolbarGeometry`; `GlyphSize` on the toolbar or a button draws icons at their own pixel size beside normal-size labels), is drawn with, `SwatchPalette`, `ImageCompare`, `CropOverlay` over an `ImageCanvas`, `PixelLoupe` beside an `ImageCanvas`); the `LogFrequencyAxis` both share); layout and containers (`DividerContainer`/`DividerZone`, `Grid`, `TabPanel`, `Card`, `Tree`, `ReorderableTree` (rows the caller draws, dragged to reorder and re-parent; reports a `ReorderableTreeMove` whose index counts the parent's children before the move, resolved by the ImGui-free `ReorderableTreeState`), `ImageCanvas`, `PropertyGrid`, `OverlayHost`/`OverlayLayer`, `ScopedDisable`, `ScopedId`); and motion and gestures (`Tween`, `Spring`, `Easing`, `InertialScroll`, `GestureDetector`/`GestureMachine`). Also thin adapters delegating to `Hexa.NET.ImGui.Widgets`: `Spinner`, `BufferingBar`, `HorizontalSplitter`/`VerticalSplitter`, `ToggleSwitch`/`ToggleButton`/`TransparentButton`/`InlineButton`, `IconTreeNode`, `EnumCombo`, `TextCenteredV`/`TextCenteredH`/`TextCenteredVH`, `ImageCenteredV`/`ImageCenteredH`/`ImageCenteredVH`/`ImageScaleTo`, `Tooltip`, `Breadcrumb`, `DatePicker`/`YearPicker`, `FlameGraph`, `FileTreeView`, `OpenFileDialog`/`SaveFileDialog`/`OpenFolderDialog`, `RenameDialog`, `DialogMessageBox`/`ShowMessageBox`, `DockedWindow`. Seven of these look like duplicates of an existing ktsu widget; most are not, and the two that are have a recommended survivor — see [Hexa-backed vs ktsu widgets](#hexa-backed-vs-ktsu-widgets) below for the pair-by-pair verdict. `DatePicker` and `FileTreeView` need a Material Icons font registered via `FontHelper.AddCustomFont(io, data, size, FontHelper.GetMaterialIconRanges(), mergeWithPrevious: true)` (not `ImGuiAppConfig.Fonts`, which applies the Nerd Font mapping); see `examples/ImGuiAppDemo`. `YearPicker` needs no icon font. `OpenFileDialog`, `SaveFileDialog` and `OpenFolderDialog` need the same Material Icons font, for their toolbar, breadcrumb and file-tree glyphs; `RenameDialog`, `DialogMessageBox` and `ShowMessageBox` need none. `DockedWindow` composes Hexa's `ImWindow` internally rather than inheriting it — subclass it, override `Title` and `DrawContent()`, then call `Show()`/`Close()`. All of the dialogs and `DockedWindow` require a per-frame deferred-drawing pump; see [Deferred Drawing](#deferred-drawing-dialogs-and-docked-windows) below. Also includes callback-driven editors: `Sequencer`, `SequenceSource`, `CurveEditor`, `CurveSource`, `CurveData`, `BezierEditor`. Unlike the dialogs above, none of these need a deferred-drawing pump; see [Callback-driven editors](#callback-driven-editors) below.
 - **ImGui.Popups** (`ktsu.ImGui.Popups`) - Modal dialogs: MessageOK, Prompt, InputString/Int/Float, FilesystemBrowser, SearchableList
 - **ImGui.Color** (`ktsu.ImGui.Color`) - Bridge between `ktsu.Semantics.Color` and ImGui. Colors are held as the semantic `Color` (linear) and `Srgb` types and converted only at the ImGui seam: `ColorImGuiExtensions` (`ToImColor`/`FromImColor`, `ToImGuiVector4`, `ToImGuiU32`) and `SrgbImGuiExtensions` (`Srgb` → `ImColor`/`ImGuiVector4`/`ImU32`, packed directly with no linear round-trip). The `ImColor` and `Srgb` `ToImGuiU32` apply the global style alpha like `ImGui.GetColorU32`; the linear `Color.ToImGuiU32` is a pure pack matching `ColorConvertFloat4ToU32`. `ImColor` extension operations: adjustments (lighten/darken, saturate/desaturate, hue offset, grayscale, invert, alpha), analysis (relative luminance, contrast ratio, perceptual distance), and contrast heuristics (`MostReadableTextColor`, `AdjustForSufficientContrast`). All color math delegates to `ktsu.Semantics.Color`. (There is no `ImColor` factory class — construct via `Color`/`Srgb` and convert.)
 - **ImGui.Styler** (`ktsu.ImGui.Styler`) - Theming system with 50+ built-in themes, scoped styling, Button.Alignment, Text.Color semantic colors, Indent utilities, Alignment helpers, theme-aware color palette (`Palette`, e.g. `Palette.Basic.Red`, `Palette.Semantic.Error`), and interactive theme browser. Color construction and manipulation live in `ImGui.Color`.

ImGui.Widgets/README.md

@@ -95,6 +95,7 @@ The widgets below are grouped by what they are for. Everything is a static metho
 - **`TabPanel`**: Tabbed interface with closable, reorderable tabs and dirty indicators
 - **`Card`**: A scoped elevated panel that draws its shadow and rounded background behind whatever the `using` block renders
 - **`Tree`**: Collapsible `Branch` and terminal `Leaf` nodes, with connector lines drawn between them
+- **`ReorderableTree`**: Rows the caller draws, laid out as a tree and dragged to reorder them or move them in and out of containers. Reports the move rather than applying it. See [Reorderable Tree](#reorderable-tree) below
 - **`ImageCanvas`**: A pannable, zoomable image canvas with a checkerboard backing for transparency
 - **`AssetBrowser`**: A virtualized grid of thumbnail tiles over a caller-owned `AssetBrowserState`, with click, Ctrl+click and Shift+click selection, arrow-key focus, Ctrl+wheel tile resizing, double-click or Enter to activate, and dragging the selection out as a payload a drop target reads with `TryAcceptAssetPayload`. Only the visible rows ask for a label or thumbnail, so fifty thousand assets cost a screenful
 - **`Toolbar`** / **`ToolbarButton`** / **`ToolbarToggleButton`** / **`ToolbarSeparator`**: A horizontal strip of buttons, each holding a glyph and a label inside one frame — glyph leading, glyph above with the label centred beneath, glyph only (the label becomes the tooltip) or label only. See [Toolbar](#toolbar) below
@@ -585,6 +586,42 @@ using (var tree = new ImGuiWidgets.Tree())
 }
 ```
 
+### Reorderable Tree
+
+A tree whose rows can be dragged. The caller flattens its own tree into rows, top first, leaving out
+the children of anything collapsed, and draws each row's content itself; the widget lays the rows
+out, draws where a drag would land, and reports the move on release. It never applies it, so the move
+goes through the caller's own model and undo history:
+
+```csharp
+ReorderableTreeRow[] rows = [new(0, false), new(0, true), new(1, false), new(1, false)];
+
+if (ImGuiWidgets.ReorderableTree("layers", rows, i => ImGui.Selectable(names[i])) is ReorderableTreeMove move)
+{
+    // move.Row moves under move.ParentRow (-1 for the top level), into the gap move.Index.
+}
+```
+
+The top quarter of a container row drops above it, the bottom quarter below it, and the middle half
+inside it. A leaf splits at the middle. Below the last row of a subtree, how far left the pointer is
+picks how far out the drop lands. A drop onto the dragged row or anywhere in its subtree is refused,
+and so is one that would leave the row where it is.
+
+`Index` counts the new parent's children **before the move**, which is the gap the insertion line was
+drawn in. When a row moves down within its own parent, its old place is among those children, so a
+caller whose insert takes the final position subtracts one in exactly that case:
+
+```csharp
+if (sameParent && oldIndex < move.Index)
+{
+    index = move.Index - 1;
+}
+```
+
+A drag starts from a press anywhere on a row once the mouse moves past ImGui's drag threshold, so a
+click that does not move is left to the row's own items. Each row is marked for probes as
+`row{index}` inside the tree's label.
+
 ### Scoped Id
 
 The scoped ID utility class helps in creating scoped IDs for ImGui elements and ensuring they get popped appropriately: