bug#19194: 24.4.50; `window-body-width' is not dynamic relative to font size changes

[martin rudalics]

>> That's what I'm trying to fathom out here all the time.  So when
>> calculating the actual height of a character as it will be displayed in
>> a window I have to apply (in some order) the height attribute specified
>> by (1) the font of the frame the window belongs to, (2) the font of the
>> buffer shown in the window, and (3) the font of the default face.
>
> We always use the current default face's font for this.  Otherwise,
> you get to a problem that IMO is insoluble even in principle.

But doesn't that imply that `frame-char-height' is just an artifact?

>> OK.  Now how do I get the `default-font-width' from that?
>
> You need help from Emacs, because it knows everything about that
> font's metrics.  But we don't have an API for that for now.

I see.  Can you provide one?

Thanks, martin