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It was documented in Windows XP but I think it was Vista that really promoted the use of that effect ("Aero" was it?). Happy to be proved wrong about Windows 20

It was documented in Windows XP but I think it was Vista that really promoted the use of that effect ("Aero" was it?). Happy to be proved wrong about Windows 2000 but I don't recall seeing any documentation on MSDN back when I was playing around with Windows APIs. I remember I pinched the API guide for XP thinking "if it works in XP then it must work in Windows 2000" and the reason I remember that so vividly was because it didn't work properly. In fact it caused a kernel panic. Which was pretty much the only time I managed to upset Windows 2000 badly enough to cause a "blue screen of death".

int_19h 7y ago
It definitely worked in 2K - there were many apps that implemented it as a bling feature as soon as it became known. The question is whether it was documented at the time. If you were able to build it for Win2K, and it compiled successfully, then it was supported - it wouldn't be in the headers otherwise. Even if you build it with XP as a target, and then run on 2K, you'd get a regular Win32 error about not being able to resolve a symbol from a DLL. Getting a BSOD indicates a driver issue. MSDN also says that it is supported for Win2K+: https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-setlayeredwindowattributes https://docs.microsoft.com/en-us/windows/win32/api/winuser/n... Aero in Vista was something else - it was the first version of Windows that did whole desktop composition, and so it could do all kinds of fancy stuff, similar to Compiz that preceded it on Linux. Transparent windows in 2K/XP used per-window composition.