ScreenFlip

A small Windows tray app that swaps your primary monitor with one click.

Prerequisites

• Windows 10/11
• .NET 10 SDK

Build

dotnet publish -c Release -r win-x64 --self-contained -p:PublishSingleFile=true

Output: bin\Release\net10.0-windows7.0\win-x64\publish\ScreenFlip.exe

Usage

Launch ScreenFlip.exe - it appears in the system tray and opens a small control window.

• Enable swaps the primary monitor to your other screen. Optionally dims the old primary with a dark overlay so you know it's inactive.
• Disable swaps back to the original primary and removes the overlay.
• The window can be closed (it minimises to tray). Double-click the tray icon or use Open from the tray menu to bring it back.
• Use Exit from the tray menu to quit fully.

Settings

The control window has a "Show overlay on inactive monitor" checkbox (on by default). When enabled, a 90% black overlay is drawn over the old primary screen while ScreenFlip is active, clearly marking it as inactive. The checkbox state is saved between runs.

How It Works

• Uses Win32 ChangeDisplaySettingsEx to reassign the primary monitor
• Stores the original primary device name in %LOCALAPPDATA%\ScreenFlip\state.txt so it can be restored on disable
• Saves the overlay preference to %LOCALAPPDATA%\ScreenFlip\settings.txt
• The overlay is a click-through (WS_EX_TRANSPARENT) WinForms window so it doesn't interfere with input on that monitor