Re: Could x-show-tip be reimplemented in Elisp? How does one create borderless frames from Elisp?

[martin rudalics <rudalics@gmx.at>]

 > TL;DR: How do I create a frame without a border, in the style of
 > x_create_tip_frame (called by x-show-tip in the C sources), from
 > Elisp?

What is a border?  ‘x_create_tip_frame’ creates a frame with up to two
types of borders, the one specified via the ‘internal-border-width’ and
the other one specified via the ‘border-width’ frame parameter (where
the latter is AFAICT used for tooltips only).  At the same time,
‘x_create_tip_frame’ tries to suppress decorations of the window manager
which is probably what you want.

 > I'm looking at ways in which we could use real tooptip popups instead
 > of overlays to display company-mode completion lists. This would have
 > many advantages, including better interaction with font sizes, no
 > issues with recursive display specs, good support for variable-width
 > fonts, and so on. I believe Stefan has spoken in favour of that
 > approach in the past, too.

Is there any reason you cannot use menus for this purpose?

 > The natural candidate for this task is x-show-tip, and it probably
 > meets most of the requirements; but not all. In particular, there can
 > be at most one tooltip displayed at any time; this means that we'd
 > break other packages that display tooltips while completion is
 > ongoing. Examples include company-quickhelp, which displays
 > documentation for the currently selected entry next to completion
 > candidates.
 >
 > `x-show-tip` is currently implemented in C; as far as I can see,
 > however, it essentially creates a frame and displays it at a given
 > location; given this, I thought it would be possible to reimplement it
 > in ELisp. Unfortunately, I've been hitting a wall when it comes to
 > displaying a borderless frame. I asked on
 > https://emacs.stackexchange.com/questions/20167/how-do-i-create-a-borderless-frame,
 > to no avail.

‘x-show-tip’ is highly tailored to emulating "conventional" tooltips and
strongly tied to ‘x-hide-tip’.  Parts of its implementation (in
particular the Lucid menubar issue) are highly fragile, so better don't
tinker with it.  Also a reimplementation in ELisp hardly makes sense
because the API calls are used to hide the implementation details wrt
X11 and Windows.  You can't use the ‘border-width’ parameter with the
latter so we have to emulate the X11 behavior somehow with the
"thin-line" border approach provided by the Windows API.  And the
GTK/OSX tooltips will behave specially anyway.

 > My original guess was that the relevant part of the C code was this call:
 >
 >    x_default_parameter (f, parms, Qborder_width, make_number (0), "borderWidth", "BorderWidth", RES_TYPE_NUMBER);
 >
 > Unfortunately, neither (set-frame-param (selected-frame) 'border-width
 > 0) nor (make-frame '((border-width . 0))) (both inspired from the call
 > above) yield a borderless frame.

These are overridden by the window manager.  ‘border-width’ is the most
obscure of our frame parameters, it's implementation is beyond our
control.  You can set it via ‘tooltip-frame-parameters’ and then it is
usually honored for X11 tooltips (but not on Windows).

 > Is there a way to create a borderless frame from Elisp?

If a truly borderless frame is what you want, we can do that for X11 and
Windows.  GTK has ‘gtk_window_set_decorated’ and we could try using that
as well.  I have no idea how to do that on OSX, maybe Anders has.

You would, however, have to say how a borderless frame should look like.
At least the Windows tooltip frame is _not_ borderless.  And on X11 I
wouldn't know how to remove caption and borders separately.  IIUC you
can only remove them both or neither.

martin