Pen Pan/Scroll for OpenTabletDriver

Wacom-style pen button-pan/scroll for OpenTabletDriver on macOS.

Hold a pen button, touch the nib, and drag: the pointer stays exactly where it was and the screen scrolls — both axes, natural direction (drag up = scroll down). Lifting the nib pauses without jumping; release the button for normal pointing.

Built for OpenTabletDriver 0.6.7 (macOS, Absolute Mode), first tested on a Wacom PTK-470. Developed by Oliver Iborra-MacDonald.

Platform support

Platform	Status
macOS	Supported — pixel-precise scrolling via OTD's macOS pointer backend
Windows	Inactive by design — the filter logs "Inactive" and passes all input through. OTD's Windows pointer backend (WindowsVirtualMouse) exposes no scroll API, so Windows support would be a separate implementation (see Forking below)
Linux	Inactive by design — the Linux scroll backend was not verified for this plugin, and the code gates to macOS anyway, so it passes input through. PRs welcome (see Forking below)

The plugin never blocks or alters input on unsupported platforms: worst case, nothing happens.

Forking for Windows / Linux

MIT-licensed — fork freely, no permission needed (keep the copyright notice). What's portable and what isn't:

• Portable as-is: the filter pipeline (IPositionedPipelineElement at PreTransform), tablet geometry + Absolute Mode, and all gesture math (anchor, pressure-zeroing, fractional accumulation). ~90% of the code.
• Not portable: the scroll sink. The filter casts OTD's live pointer to IMouseScrollHandler. macOS implements it with pixel precision; Windows does not implement it at all (verified in OTD source); Linux is unverified and the current code's OperatingSystem.IsMacOS() gate blocks it regardless.
• What a port needs: remove/extend the OS gate, then emit scroll through the target OS — on Windows that's SendInput MOUSEEVENTF_WHEEL/HWHEEL in WHEEL_DELTA (120) units rather than pixels, so sensitivity needs re-scaling; on Linux it means checking the current backend's name/path and emitting the equivalent wheel events. Either way it needs a real tablet + OTD 0.6.7 on that OS to verify feel — no Mac-side test can prove it.

How it works (short version)

The filter sits in OTD's input pipeline before coordinate transformation. While the chosen pen button is held and the nib is touching:

• the pointer anchors (position frozen, pressure zeroed — no accidental clicks or drags),
• pen travel is converted to scroll pixels (pixels = mm × sensitivity), with sub-pixel motion accumulated so slow drags stay smooth,
• both scroll axes queue on OTD's own macOS virtual mouse and flush through its normal output cycle — no second, conflicting pointer.

Direction is tuned to macOS natural scrolling: upward pen motion scrolls the page down. Each axis is independently reversible and can be disabled (sensitivity 0).

Install

1. OpenTabletDriver 0.6.7 on macOS, in Absolute Mode.
2. Either:
   • Plugins tab of OpenTabletDriver → drag and drop PenPanScroll-1.0.0.zip from the Releases, or
   • close OTD, create ~/Library/Application Support/OpenTabletDriver/Plugins/PenPanScroll/ and put PenPanScroll.dll inside it (any folder name works; version lives in the plugin metadata, not the folder).
3. Restart OTD → Filters → enable Pen Pan/Scroll → set your scroll button → Save.
4. Optionally drop a metadata.json next to the DLL (see metadata.json in this repo) so the Plugin Manager shows owner/license/description.

Keep the filter first in the filter list if you have other filters that alter position, pressure, or buttons.

Use

1. Point at the scrollable content.
2. Hold pen button 1 (default) and touch the nib to the tablet.
3. Drag up to scroll down, sideways to scroll horizontally.
4. Lift the nib to reposition; touch down for another stroke.
5. Release the button to resume ordinary absolute pointing. If the nib is still down, lift it before clicking again.

Your other pen buttons keep their existing bindings (e.g. button 2 right-click). There is no momentum; the app must support normal mouse-wheel/pixel scrolling.

Settings

Setting	Default	Meaning
Scroll button	1	One-based pen button that triggers panning (see OTD's debugger to identify). Its normal binding is suppressed while panning
Horizontal / Vertical sensitivity	10 px/mm	Scroll pixels per mm of pen travel. 0 disables that axis. 0–1000
Reverse horizontal / vertical	off	Invert that axis

Build & test

Requires the .NET 8 SDK and an installed OpenTabletDriver 0.6.7 app. No NuGet packages are downloaded (references come from the installed app).

dotnet build src/PenPanScroll.csproj -c Release
dotnet run --project tests -c Release

If OTD is installed elsewhere, pass -p:OtdDirectory=/absolute/path/to/OpenTabletDriver.app/Contents/MacOS. The compiled plugin is src/bin/Release/net8.0/PenPanScroll.dll. For direct installation, package that DLL together with the root metadata.json; keep both files at the archive's top level.

Tests drive the real OTD report, binding, and absolute-output classes with a recording pointer: direction, anchoring, fractional accumulation, lift/re-contact, both button-release orders, right-click preservation, proximity loss, disposal, and fail-open behavior. They do not substitute for physical tablet testing.

Releasing a new version

1. Bump <Version> in src/PenPanScroll.csproj and PluginVersion in metadata.json (four-part, e.g. 1.1.0.0).
2. dotnet build src -c Release, then package the DLL into a zip named after the release (DLL at the archive's top level) and upload it to a GitHub Release.
3. If the plugin is in the OTD marketplace, update DownloadUrl/SHA256/PluginVersion in marketplace/ and open the PR.

Sharing via the OTD marketplace

marketplace/ contains the metadata JSON for the OpenTabletDriver Plugin Repository (optional — the repo + Releases work standalone). File path in the marketplace: Repository/{DriverVersion}/{Owner}/{Repo}/PenPanScroll.json.

License

MIT — do whatever you want, no warranty. OpenTabletDriver itself is LGPL-3.0; this plugin only references its public API.