Many Windows applications choose to remove the system window borders on their main window. The naive way of doing this is to create a popup window (with the WS_POPUP style) instead of an overlapped window, however popup windows are more suited to things like splash screens and other overlays, not main application windows. They lack a number of useful behaviours such as window snapping and the window menu, so they can be frustrating for users who expect these behaviours.

The proper way to create a borderless application window is to create a regular overlapped window and remove the borders by expanding the client area. This is what Office, Visual Studio, iTunes and UWP CoreWindows do, however doing this exposes some quirks in the windowing system that must be worked around in each application.

borderless-window is a minimal demonstration of how to work around these quirks. It creates a window that:

• Works with window snapping, including double-click to snap vertically
• Works with Aero Flip 3D
• Obeys the "minimize all" command (Win+M)
• Obeys the cascade and tile commands
• Shows a window menu when Alt+Space is pressed
• Does not cover the taskbar when maximized
• Does not disable auto-hide taskbars when maximized
• Casts a drop-shadow, like other top-level windows
• Has hide, show, maximize, minimize and restore animations, like other top-level windows
• Can be resized by the user
• Does not accumulate visual corruption in the client area from the hidden window borders when the window is activated, the window text is changed or the window menu is opened

A Makefile is included for mingw-w64 GCC. The C source should also compile in Visual Studio 2015 with a recent Windows SDK. The generated binary should be compatible with Windows Vista and up. It will not work unmodified on Windows XP due to the hard dependency on dwmapi.dll.

This project is a demonstration of something simple that is made unnecessarily difficult by quirks in the Windows API. In order to be as useful as possible to as many application developers as possible, it is placed in the public domain. Attribution would be appreciated, but is not required (after all, this stuff should have been documented by Microsoft.)

To the extent possible under law, the author(s) have dedicated all copyright and related and neighboring rights to this software to the public domain worldwide. This software is distributed without any warranty.