PDFInk

Native macOS PDF annotation app (AppKit + PDFKit) with full Wacom tablet support: pressure-sensitive pen, highlighter, stroke-level eraser, and eraser-flip via stylus proximity events. No PencilKit — the drawing canvas is a custom NSView overlay.

Build & run

make app                        # builds dist/PDFInk.app
open dist/PDFInk.app            # or: dist/PDFInk.app/Contents/MacOS/PDFInk file.pdf
make test                       # unit tests (coordinate transforms, serialization)

Only the Xcode Command Line Tools are required. Note for this machine: the CLT install is half-updated and two workarounds are active — see scripts/fix-clt.sh (stale duplicate SwiftBridging modulemap masked via -vfsoverlay; the reason every swiftc invocation carries that flag) and scripts/fix-swiftpm.sh (stale SwiftPM manifest interfaces). The Makefile drives swiftc directly; Package.swift is kept so the project opens in Xcode/SPM once a healthy toolchain is installed (swift build will then work with SWIFTPM_CUSTOM_LIBS_DIR per fix-swiftpm.sh, or unmodified after a CLT reinstall).

Features

• Open PDFs via File ▸ Open, drag-and-drop, or CLI argument; continuous vertical scroll with a page-thumbnail sidebar (PDFThumbnailView).
• Tools: pen (pressure 0.5–4 pt at medium width), highlighter (constant width, 40% alpha, multiply blend), stroke-level eraser, lasso (stubbed). Keyboard: ⌘1/⌘2/⌘3. 6 preset colors + custom (NSColorPanel), 3 width presets.
• Wacom: NSEvent.subtype == .tabletPoint pressure drives stroke width; tilt is logged; flipping the stylus to its eraser end auto-switches tools via .tabletProximity monitoring. Mouse/trackpad falls back to constant pressure.
• Strokes are stored in PDF page space and stay registered at any zoom (pinch or ⌘+/⌘−). Committed strokes render from per-page bitmap caches; the live stroke draws incrementally with Catmull-Rom smoothing.
• Undo/redo per stroke (NSUndoManager, preserves z-order on reinsert).
• ⌘S writes strokes as PDF ink annotations in place — visible in Preview, Acrobat, etc. Full-fidelity stroke JSON (per-sample pressure) is stashed in each annotation, so PDFInk re-opens its own annotations as editable strokes.
• File ▸ Export Flattened PDF burns the ink (with pressure-varying widths) into page content.
• Autosave drafts every 30 s (and at quit) to ~/Library/Application Support/PDFInk/Drafts/; unsaved ink is restored on next open.
• Whiteboards (notebook mode): File ▸ New Whiteboard — Blank (⌘N), Grid, or Lined paper. Created as real PDFs in ~/Documents/PDFInk Whiteboards/ and auto-saved notebook-style. Add Page (⌘⇧N) appends a matching page (works on opened PDFs too, appending a blank page).

Architecture

Component	File	Role
DrawingCanvasView	Sources/PDFInk/	Input (mouse/tablet), live rendering, per-page bitmap caches
StrokeStore	Sources/PDFInkCore/	Model: strokes per page in page space, hit-testing, JSON
StrokeGeometry	Sources/PDFInkCore/	Pressure→width, Catmull-Rom, page↔view affine transforms
StrokeRenderer	Sources/PDFInkCore/	Stroke → CGContext (canvas cache + flattened export)
AnnotationSerializer	Sources/PDFInkCore/	Stroke ↔ PDFAnnotation (PDFKit bridge)
ToolState	Sources/PDFInk/	Current tool/color/width, eraser-flip state
AutosaveManager	Sources/PDFInk/	30 s draft autosave to Application Support
FlattenedExporter	Sources/PDFInk/	Flattened PDF export via CGContext

A stroke is an array of (point, pressure) samples plus tool metadata. All page↔view mapping goes through PDFView's convert APIs; the canvas derives exact affine transforms from three reference points (covers scale, translation, and flips), unit-tested in Tests/PDFInkCoreTests.