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Re: Win32 WM_NCDESTROY to GDK Window to GTK Widget signal




On 19.09.2018 19:40, Michel Donais wrote:
> So, the code actually works using append_event, but it might not be the
> best solution, as the WM_NCDESTROY event is terminal, so merely appending
> an operation for future consideration is probably not the best case.
> 

This got me thinking: why exactly does GTK not handle WM_DESTROY? That is a
message that child windows get before they are destroyed, whereas WM_NCDESTROY
is only sent after everything is supposed to be dead.

According to commit 820721500b4f215eebda1f2466bf4166922bfa1e, this was done
deliberately.

I've looked at XOrg[1] manual, and it seems to agree with that - DestroyNotify
is called bottom-up (children first, parent last), and the X11 window can't be
referenced after that message is received (or processed?).

So yeah - it kind of works just like WM_NCDESTROY.

After that i've looked at gdk_x11_window_destroy_notify().
It checks for the GDK window not being destroyed yet, and if it isn't, the
window is destroyed (it warns if this is done for a non-foreign window), then
detaches the GDK window from GDK display, clears its grab, if any, and unrefs it.

The GDK_WINDOW_DESTROYED() (the ->destroyed field) is weird. It is only set to
TRUE by _gdk_window_destroy_hierarchy(), which sets it *after* it calls
impl->destroy() (which results in XDestroyWindow on X11; i.e. normal windows
are supposed to be XDestroyWindow-ed first, which will cause DestroyNotify,
which will be handled in gdk_x11_window_destroy_notify(), and only after that
the ->destroyed field will be set to TRUE, which will allow
GDK_WINDOW_DESTROYED() to evaluate to TRUE). I don't understand why
gdk_x11_window_destroy_notify() doesn't warn about non-foreign windows being
destroyed all the time.

W32 backend does it differently - it explicitly sets ->destroyed to TRUE before
calling DestroyWindow().

What a mess...

[1]: https://www.x.org/archive/X11R7.5/doc/man/man3/XDestroyWindow.3.html

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