Running your own app at the click of the Surface Pen button

Thursday, I picked up a Surface 3 — my first Surface with pen input — and was surprised at the lack of customization options for the pen's top button. Searching around, I found some clever hacks using AutoHotkey and EventGhost but I wasn't really interested in installing middleware. So I took a peek under the hood and found an inbox solution instead.

Thankfully, Microsoft was nice enough to bake in some overrides for which app gets launched. These overrides, unsurprisingly, live in the Lockscreen ClickNote component (lockscreencn.dll).

Upon every click of the pen button, this component reaches out to a registry key, specifically \Software\Microsoft\Windows\CurrentVersion\Authentication\LogonUI\CN.

It looks for an AppID or DesktopAppPath value and if one is found, retrieves its data and executes an immersive or desktop app accordingly. Otherwise, OneNote is launched via a built-in AppID: Microsoft.Office.OneNote_8wekyb3d8bbwe!Microsoft.OneNoteIm

Before you go stuffing Notepad or your app into the DesktopAppPath value, be aware that the path is passed through GetFileAttributes to test for existence. And before passing through ShellExecuteEx, a command line argument of /screenclip, /fromlockscreen, or /hardwareinvoke is tacked on, depending on how the button is clicked or the state of the Surface at time of click. So, for example, if you want to avoid Notepad complaining about the lack of a /hardwareinvoke.txt, you will want to wrap it in a script.

I haven't spent much time on the immersive app side, so am eager to see what folks do in that space. I plugged in FreshPaint's AppID, for example: Microsoft.FreshPaint_8wekyb3d8bbwe!Microsoft.FreshPaint

... and had mixed (but mostly positive) results.

Free idea corner: PowerPoint could benefit from button-based slide navigation. An app-aware button remapping hub would be cool too.