A window possesses a visibility state indicated by the WS_VISIBLE style bit. When the WS_VISIBLE style bit is set, the window is shown and subsequent drawing into the window is presented, unless that window is obscured by some other window, or at least one of the windows upward in the parent chain from hwnd does not have the WS_VISIBLE style.

When the WS_VISIBLE style bit is not set, the window is not shown ("hidden") and subsequent drawing into the window is not presented, even if that window is not obscured by another window.

If the value of the WS_VISIBLE style bit has been changed, the WM_SHOW message is sent to the window of hwnd before the function returns.