>>109526891
Your process
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| CreateWindowA()
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USER32.DLL
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| converts ANSI -> Unicode, eventually CreateWindowExW
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| NtUserCreateWindowEx(...)
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---------------- kernel boundary ----------------
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win32k.sys / win32kfull.sys / win32kbase.sys
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| creates/manages HWND, window hierarchy,
| input state, window manager objects, etc.
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Kernel-mode Win32 window manager
On windows, window manager is kernel mode which is why windows XP with full compositor is still faster than just bare X11 with no compositor. If you drag a window on really old hardware (or a VM with very low power settings), you will notice a lot more lag with X11 than with Windows XP