SketchControl in Novolis.Avalonia.Controls

name: Avalonia Sketch Control overview: Add SketchControl to Novolis.Avalonia.Controls — Excalidraw-inspired freehand strokes that become selectable/resizable shapes, with a resizable grid and on-demand Gridify. Single package; Avalonia + Novolis + nuget.org only. todos:

• id: document-core

content: Add SketchDocument, StrokeShape, grid snap, bounds transform, undo stack, SketchJson under Novolis.Avalonia.Controls status: completed

• id: gridify

content: Implement Gridify (quantize + dedupe) with unit tests in Controls/ status: completed

• id: sketch-control

content: "Implement SketchControl: pen, select/move/resize, pan/zoom, grid render, Gridify API" status: completed

• id: readme-verify

content: Update Controls README + build/test verification status: completed isProject: false

Placement

Home: `Novolis.Avalonia.Controls` — new SketchControl (and supporting types) in namespace Novolis.Avalonia.Controls.

No new packages. Do not create Novolis.Sketch or Novolis.Avalonia.Sketch. Document model, Gridify, JSON helpers, and the Avalonia control all live in Controls.

Dependencies (only):

• Existing: Avalonia, Avalonia.Controls.DataGrid, Novolis.Avalonia.Layout (csproj)
• Optional adds: only free, maintained packages from nuget.org if needed (prefer BCL System.Text.Json — already available). No Novolis.IO, no local feeds, no unmaintained/sketchy deps.

MVP scope (v1): freehand pen → stroke shapes, select / move / resize, pan/zoom, visible resizable grid, snap-while-draw/edit toggle, Gridify on selection (or all). Undo/redo via a small command stack. Out of v1: rect/ellipse/arrow/text, rough-js style, collaboration.

Document model (same package)

Pure C# types in Controls (testable without UI when logic is extracted, same pattern as ChoiceDialogLogic):

flowchart LR
  pointer[Pointer strokes] --> draft[InProgressStroke]
  draft -->|pointer up| shape[StrokeShape in Document]
  shape --> select[Select / move / resize]
  shape --> gridify[Gridify algorithm]
  grid --> snap[Snap while edit]
  grid --> gridify
  doc[SketchDocument] --> json[SketchJson]

• `SketchDocument`: elements list, selection ids, GridSettings (Size, Visible, SnapEnabled), Version.
• `StrokeShape`: id, points (world double X/Y), stroke color/width. Bounds = AABB.
• Resize: ApplyBoundsTransform(oldBounds, newBounds) scales points with the AABB.
• JSON: SketchJson.Serialize / Deserialize via System.Text.Json (in-package helpers — not Novolis.IO).

Gridify

On-demand (not only snap-while-drawing):

1. For each selected StrokeShape (or all if none selected): snap every point to nearest grid intersection using current GridSize.
2. Collapse consecutive duplicates.
3. Light cleanup only (no heavy simplification engine).
4. Undoable via the document command stack.

Unit tests under `tests/Novolis.Avalonia.Unit/Controls/`.

Avalonia control (`SketchControl`)

Follow `StarMapControl`: inherit Control, StyledProperty + InvalidateVisual, override Render(DrawingContext). Code-only (no XAML / ControlThemes).

API:

• Document, Tool (Pen | Select)
• GridSize, GridVisible, SnapEnabled
• GridifySelection(), Undo(), Redo(), Clear()
• DocumentChanged, SelectionChanged

Render order: grid → strokes → selection/grips → in-progress stroke.

Suggested files under src/Novolis.Avalonia.Controls/:

• SketchControl.cs — control + pointer/render
• SketchDocument.cs, StrokeShape.cs, GridSettings.cs — model
• SketchGridify.cs, SketchBounds.cs — pure logic
• SketchJson.cs — serialize
• SketchHistory.cs — undo/redo

Scaffolding / packaging

1. Add types + control to existing Controls project (no slnx / packages.json package adds).
2. Update Controls `README.md` + package Description to mention sketch.
3. Unit tests for Gridify, snap, bounds transform, JSON round-trip.

Explicit non-goals (v1)

• No separate Sketch NuGet package.
• No Novolis.IO dependency.
• Do not reuse DraftStudio CAD / .cadjson.
• Imperative DrawingContext only (no Avalonia Shape visual tree).
• No rough/hand-drawn stroke styling yet.

Verification

• dotnet test Controls unit tests exit 0.
• dotnet build Novolis.Avalonia.Controls.
• Smoke: draw → select → resize → change grid size → Gridify → undo.