Floating overlay that stays out of screen-share captures on Windows

A live call assistant is useless if the other person sees the overlay the moment you share your screen. On Windows there are a few reliable techniques.

Window flags that matter

• WS_EX_LAYERED + WS_EX_TRANSPARENT for click-through when needed.
• WS_EX_TOPMOST so the panel stays above the meeting window.
• SetWindowDisplayAffinity with WDA_EXCLUDEFROMCAPTURE (Windows 10 2004+) to exclude the window from most capture APIs.

Practical notes

• Test with the actual screen-share preview, not just a screenshot tool. Zoom, Teams and Meet use slightly different capture paths.
• The protection is not absolute — some recording tools and older Windows versions ignore the affinity flag.
• Keep the panel small and movable; users will drag it to a corner of the second monitor or hide it with a hotkey.

The combination gives a usable overlay that is invisible to the other party in normal screen-share scenarios while remaining fully interactive for the user.

I'm building Talkaside, a Windows app for job interviews and calls in another language.

Drafted with AI assistance from this project's code and logs.