bug#19395: 25.0.50; Setting left fringe to 0 messes up window-width

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 20 Dec 2014 15:51:12 +0100
> From: martin rudalics <rudalics@gmx.at>
> CC: malsburg@posteo.de, 19395@debbugs.gnu.org
> 
>  >> (with-selected-frame some-frame
>  >>     (with-current-buffer a-buffer-not-displayed-on-some-frame
>  >>       ...
>  >
>  > Which makes it "displayed", as far as Emacs is concerned, right?
> 
> You mean as far as the Emacs display engine is concerned, right?  But
> the caller of `face-font' doesn't know that the display engine operates
> on the current buffer regardless of whether it is displayed or not.

She doesn't need to know: the effect doesn't depend on that.

> (1) When two characters have the same face they are identic in their
>      appearance on screen.
> 
> (2) When two characters have a different appearance on screen they have
>      different faces.

I think YES to both, assuming both characters are on the same frame.
If not, then (2) might be false.

> For me it's difficult to discriminate the usage of the term "face" when
> programming Elisp from the usage of the term "face" when Emacs displays
> a character.

I was primarily talking about the latter.  But the different is small,
if it exists at all.

>  > face-remapping-alist is applied _after_ the frame-specific face is
>  > retrieved.  Does that answer your problem?
> 
> What means "applied"?  Is it merged or does it replace the
> frame-specific face?

It replaces the original frame-specific face.

>  >> IIUC face remapping maps a default face (which may be frame specific or
>  >> not) via a scaling value (which may be buffer local or not) to another
>  >> face whose width I eventually want to retrieve via `face-font'.  Does
>  >> the buffer/frame/window relationship affect that value and if so how?
>  >
>  > AFAIK, only the buffer matters, since face-remapping-alist is
>  > buffer-local.
> 
> It's doc-string says
> 
>    If this variable is made buffer-local, the face remapping takes effect
>    only in that buffer.

OK, _if_ face-remapping-alist is buffer-local.