bug#35079: 26.1; Font rendering - problem with bdf fonts

[Eli Zaretskii <eliz@gnu.org>]

> From: Max Xiong <xsrvmy@gmail.com>
> Date: Tue, 2 Apr 2019 01:31:09 -0400
> 
> When loading a bdf or a pcf font, specifically unifont in my case, the width of characters is incorrect.

Does this happen only with Unifont, or with any BDF font?

> To reproduce:
> Download the bdf.gz file from the unifont website at http://unifoundry.com/unifont/index.html
> Change the extension to .bdf
> Install the font. In my case, I needed to copy it to ~/.local/share/fonts/misc/
> Run fc-cache -fv in the terminal.
> Start emacs.
> From the menu bar, choose options -> select default font.
> Search for and choose Unifont Sans Serif size 12 (size should go to 12 anyways).
> 
> The unexpected result is that each character is rendered with a full width, as if there is a space after it. The
> cursor becomes square instead of a half-width rectangle.

This could be the realization of the danger described in the
commentary to ftfont.c:get_adstyle_property, or some other issue with
BDF fonts.  I don't think they are used widely anymore, so maybe our
code accrued some bitrot.

> Additionally, note that this does NOT occur with the ttf version of unifont. Nor does this bug occur when I use
> the bdf unifont inside the gnome terminal.

CC'ing Handa-san, in the hope that he could look into this issue.

Thanks.