[rustycawk]

Brings the Draw tab closer to Excel's. Ink gets a typed model with pressure, Excel's InkML file format, editable pens and erasers, and Draw with Trackpad with Force Touch pressure on macOS.

What changes for users

• Pens: an editable pen gallery (pen, pencil, highlighter) where each pen has a colour, a width and an optional effect (rainbow, galaxy, gold…). Pens can be added and removed.
• Erasers: a stroke eraser, a segment eraser that cuts at crossings, and small and medium erasers. Each eraser drag is one undo step.
• Lasso: a freehand loop selects ink, which can then be moved or deleted.
• Stroke width: width follows pressure when the input reports it, and drawing speed otherwise.
• Fast strokes keep their shape, like Excel:
  • a stroke takes every pointer move and keeps following the pointer past the cells (over the headers or out of the window); the grid clips what lies outside;
  • smoothing only settles jitter (at most 1.5 px) and uses a centripetal spline through the samples, so a fast zigzag keeps sharp, full-height turns instead of curling into loops;
  • on macOS, while a Draw tool is on, mouse drags aren't coalesced, and a hard press on the trackpad mid-stroke doesn't force-click.
• Draw with Trackpad: a floating canvas over the sheet. One finger draws, two fingers move the canvas, and any key exits.
  • On macOS, a light touch draws the thinnest line; clicking the pad down and pressing harder thickens it. It uses NSPressureBehavior.primaryGeneric, so there is no force click or Look Up.
  • Backends: macOS (AppKit touches), Linux (evdev) and Windows (precision-touchpad HID). The device is probed off the main thread and opened only when the mode starts.
• Files: XLSX ink is saved as Excel InkML behind mc:AlternateContent, with a DrawingML fallback for readers without InkML. Plain DrawingML polylines from Preserve editable ink strokes across XLSX saves #712 still open as editable ink.
• Print and PDF: highlighter and pencil ink print translucent, and effect strokes print in their colours.

Commits

One commit per layer, in dependency order: model → PDF → XLSX → engine → UI → app (trackpad backends) → docs. Each commit passes cargo check --all-targets for the crates it touches. The whole branch passes cargo xtask ci (fmt, clippy, test, assets, layers, wasm, parity, keytips).

Notes for review

• macOS UI freeze when the trackpad mode starts (fixed). Draining touch events with nextEventMatchingMask in the default run-loop mode inside winit's redraw handler re-entered winit's and Core Animation's observers. nextDrawable then hit its 1 s timeout. Touch events are now drained in a private run-loop mode.
• Known limitation: Force Touch pressure lags a little. winit dispatches pressure events between frames, so a per-frame poll mostly sees NSApp.currentEvent. Seeing every event would need addLocalMonitorForEventsMatchingMask:handler:, which is an unsafe fn in objc2, and the workspace forbids unsafe. A new finger identity always starts a new stroke, so a missed lift doesn't join two strokes.
• Not yet tested on physical Linux and Windows touchpads. Those backends have synthetic-input tests only.
• Shared crate: the app-independent parts (ink model, InkML, trackpad capture, Draw widgets) are proposed for craft-libs in RFC: a shared Draw stack for the Craft apps (craft-ink, craft-trackpad, Draw components in craft-ui) craft-libs#99.

Testing

• Unit and UI tests:
  • ink model, InkML import and export, and the DrawingML fallback, all with hostile-input bounds;
  • segment eraser and lasso;
  • smoothing keeps a fast zigzag's turns, and a stroke follows the pointer past the cells (both tests fail without the fix);
  • trackpad frames, including Force Touch press and a press in place;
  • native AppKit mouse events never reach the touch or pressure accessors.
• Manual testing on a MacBook with a Force Touch trackpad:
  • the mode starts without a UI freeze;
  • touch strokes are thinner than clicked ones, and pressing harder thickens the line;
  • a fast swipe off the edge no longer joins strokes.
  • fast zigzags drawn by clicking and dragging on the trackpad now match Excel's (turns run the full height, no loops).

[alosslessdev]

Superseded Draw-tab PRs

We are closing the small Excel-parity Draw PRs in favour of this work. The issues they targeted should be tracked here:

• Draw tab: control order matches Excel (Select, Eraser, pen set, Ink to Shape) #1783 — Draw tab control order (Select, Eraser, pen set, Ink to Shape)
• Draw tab: pen buttons show their colour and thickness (labels and icons) #1784 — Pen buttons show their colour and thickness
• Draw tab: pen split buttons with thickness and colour menus #1785 — Pen split buttons with thickness and colour menus
• Draw tab: live stroke preview uses the selected pen's colour and thickness #1786 — Live stroke preview uses the selected pen's colour and thickness

This PR replaces the fixed-pen Draw tab with the editable pen gallery and shares stroke_shape() between the live preview and draw.stroke, so the preview/commit mismatch those PRs patched no longer exists in the same form. If this PR lands, those issues are covered by it.

Still separate and not covered here:

• Draw: Ink to Shape mode, ported from WordCraft's recogniser #1776 / Draw: Ink to Shape parity (mode-before-draw and Excel's shape set) #1775 — Ink to Shape mode and the WordCraft recogniser (crates/engine/src/cmd/ink_shape.rs). Draw: Ink to Shape mode, ported from WordCraft's recogniser #1776 stays open.
• Draw: Action Pen — handwriting recognition (ink to text) #1777 — Action Pen handwriting recognition.

Round-trip evidence for this PR's InkML work

Excel 16.0 (Build 20430) writes a Draw-tab stroke as xl/ink/ink1.xml (InkML with X/Y in 1/1000 cm and first/second differences) referenced by mc:AlternateContent/xdr:contentPart, plus a PNG fallback. On current main, GridCraft imports only the fallback (gridcraft-cli info: images: 1, shapes: 0), so the stroke is not editable ink. crates/xlsx/src/inkml.rs is the fix; it would be valuable to land that part even if the trackpad/pen-gallery work is split.