I appologize, I was too fast to answer, I made a bad call from
modify-frame-parameters
when I tested it. It works like a charm as you say it in english. I have
also changed
the else-if statement in Martins method to else if (!NILP (new_value) &&
FRAME_UNDECORATED (f))
(check for !NILP) so I can switch back decorations. It works. Thanks all,
it was great
exercise to learn a bit of emacs internals and to make a simple hack.

2017-01-11 8:08 GMT+01:00 Arthur Miller <arthur.miller.no1@gmail.com>:

> "We call it "Losedows" or "Lose OS", because if you use it, you lose
> your freedom.
>
> We're glad if Emacs gives you a taste of freedom, but a taste is
> all it can give you.  To escape from Microsoft's power, you need to
> stop using Losedows."
>
> Haha :-) Indeed.
>
> I do run Arch Linux otherwise, but I do some consulting with programming
> databases and GUIs in access & spss and I also play some games
> occasionally, so I still need losedows. I know I could run it in wine and
> pass through vga, but I feel a bit too old for that :).
>
> This was a great excursion in Emacs src code. I added above mention
> method to my w32fns.c, added FRAME_DECORATED() macro to frame.h
> a boolean_bf undecorated :1, to frame struct, initiated it to false in
> "make_frame"
> added an entry to frame_parms: {"undecorated",        SYMBOL_INDEX
> (Qundecorated)},
> added connecction to w32_frame_parm_handlers[] to x_set_undecorated at same
> place where symbol is declared in frame_parms (last in the list), added an
> INLINE void fset_undecorated( ... ) to frame.h (not sure if it is needed),
> and now
> I can change my new param with lisp from emacs, but my connection seem
> never to be called.
>
> By the way, I think world is better without borders, so I have modified
> Martin's
> x_set_undecorated to
>
> void
> x_set_undecorated (struct frame *f, Lisp_Object new_value, Lisp_Object
> old_value)
> {
>   HWND hwnd = FRAME_W32_WINDOW (f);
>   DWORD dwStyle = GetWindowLong (hwnd, GWL_STYLE);
>   /*Lisp_Object border_width = Fcdr (Fassq (Qborder_width,
> f->param_alist));*/
>   /*Lisp_Object undecorated = Fcdr (Fassq (Qundecorated,
> f->param_alist));*/
>
>   block_input ();
>   if (!NILP (new_value) && !FRAME_UNDECORATED (f))
>     {
>       dwStyle = (dwStyle & ~WS_THICKFRAME & ~WS_CAPTION);
>       SetWindowLong (hwnd, GWL_STYLE, dwStyle);
>       SetWindowPos (hwnd, HWND_TOP, 0, 0, 0, 0,
>                     SWP_NOSIZE | SWP_NOMOVE | SWP_NOZORDER | SWP_NOACTIVATE
>                     | SWP_FRAMECHANGED);
>       FRAME_UNDECORATED (f) = true;
>     }
>   else if (NILP (new_value) && FRAME_UNDECORATED (f))
>     {
>       SetWindowLong (hwnd, GWL_STYLE, dwStyle | WS_THICKFRAME | WS_CAPTION
>                      | WS_MAXIMIZEBOX | WS_MINIMIZEBOX | WS_SYSMENU);
>       SetWindowPos (hwnd, HWND_TOP, 0, 0, 0, 0,
>                     SWP_NOSIZE | SWP_NOMOVE | SWP_NOZORDER | SWP_NOACTIVATE
>                     | SWP_FRAMECHANGED);
>       FRAME_UNDECORATED (f) = false;
>     }
>   unblock_input ();
> }
>
> So it should just switch on "undecorated" param and ignore borders (at
> least I hope). I am not sure where do
> I have to make change more to get it to work.
>
> 2017-01-10 21:39 GMT+01:00 Clément Pit--Claudel <clement.pit@gmail.com>:
>
>> On 2017-01-10 13:27, Eli Zaretskii wrote:
>> > Then I suggest to add this to Emacs.  That some wm's ignore it is not
>> > a reason to avoid having the feature for those that don't ignore it.
>>
>> Indeed, it would be wonderful!
>>
>>
>