I'm starting off what might become a moderately-sized program, but anticipate that in most cases it will comprise a main window with between zero and two others docked to the RHS. I'm currently using GTK2, but could switch easily to Qt5 for testing.
I've got a couple of early-stage questions, which I'll pose individually.
I'm controlling the making the subsidiary windows visible using menu entries with checkboxes. So irrespective of whether one of them is docked or undocked, if it is displayed somewhere on the screen (i.e. possibly slipped under some other window) the corresponding checkbox is marked (i.e. "checked", "ticked" etc.).
If a subsidiary form is undocked and its main close button is clicked, its Visible property becomes false. This may be tracked by the checkbox.
If the small cross on a (docked or undocked) subsidiary window's dock header is clicked, the window disappears but its Visible property remains true.
How can I detect in this case that the window is no-longer visible, so that the checkbox state can be kept in step?
MarkMLl