Re: question about `display-graphic-p' and emacs daemon

[Eli Zaretskii <eliz@gnu.org>]

> From: "Drew Adams" <drew.adams@oracle.com>
> Date: Wed, 21 Nov 2012 07:16:16 -0800
> 
> But shouldn't it be possible for Emacs to determine the display type without
> actually displaying a frame?

Why do you need that?  The display-*-P functions are mainly for
testing what the current frame can or cannot do, so that Lisp
applications could fall back on alternative methods if the best
alternative cannot be supported.  E.g., if fringes are not available,
a Lisp program could display something in an overlay or in margins.

If you want to know whether the current Emacs executable can do
something, it is better to use fboundp and featurep instead.

> 2. While looking for the answer, I checked the doc for `display-graphic-p'.  It
> says that argument DISPLAY can be a display name, as an alternative to being a
> frame name or nil.  But it says nothing about what a "display name" means wrt
> Emacs Lisp.
> 
> What form does it take?  Is it a Unix/Linux X-Window display name?

Yes.  A cross reference to "Multiple Terminals" would be good there.

> What about on MS Windows?

The Windows build does not support multiple displays.

> The closest I found to describing DISPLAY is in `Multiple Terminals'.  It
> describes X-Window displays as having names of the form HOST:SERVER.SCREEN.
> What about non X-Window displays?

There are none; X-Window displays are the only ones Emacs supports.

> If I eval (x-display-list) on MS Windows I see ("w32"), but I don't see that
> form of DISPLAY described anywhere.

That's a fake name, just so that code that looks at this will have
some string to play with.  It has no meaning.

> And I see that (framep (selected-frame)) returns `w32' (a symbol
> this time).

Yes, and that one _is_ documented.