Non-rectangular windows created via Win32 HRGN and SetWindowRgn peaked in the XP era with skeuomorphic apps but declined as platform priorities shifted to consistency and abstraction. The primary source demonstrates CreateEllipticRgn, SetWindowRgn, and message-loop handling for WM_LBUTTONDOWN to enable dragging yet does not address subsequent OS changes. (https://warped3.substack.com/p/direct-win32-api-weird-shaped-windows)

Raymond Chen's The Old New Thing blog documents that region-clipped windows conflict with Aero snapping, per-monitor DPI awareness added in Windows 8.1, and DWM compositing introduced in Vista, which preferred WS_EX_LAYERED with UpdateLayeredWindow for effects; Microsoft Learn confirms SetWindowRgn excludes non-region pixels from hit testing and painting, complicating accessibility tools. (https://devblogs.microsoft.com/oldnewthing/; https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-setwindowrgn)

Electron adoption after 2015 and Microsoft's Fluent Design emphasis further reduced direct Win32 usage, trading custom identity for cross-platform speed and standardized controls; original coverage missed that the API still functions on Windows 11 but production patterns show accessibility, maintainability, and security boundaries favor rectangular abstraction over bitmap-shaped mascots or hardware-mimicking media players.