[NTG-context] what defines the font size?

Arthur Reutenauer arthur.reutenauer at normalesup.org
Wed Oct 17 11:02:54 CEST 2018

On Tue, Oct 16, 2018 at 07:48:41PM +0200, Pablo Rodriguez wrote:
> I cannot claim that I understand his explanation, but it seems that
> there is something about the em quad

  The em quad has the same width as the font size, that’s correct.  But
it still doesn’t mean that any part of any glyph in the font has that
length.  It’s really a tautology, actually: if you take a font at size,
say, 12pt, then the em space is 12pt wide.  That’s the definition (at
least in the TeX world).

  It’s less clear what you’re trying to do next:

>     \setupframed
>         [offset=none,
>          framecolor=red,
>          rulethickness=0.01pt,
>          width=12pt,
>          height=12pt]
>     \starttext
>         \startTEXpage[offset=1em]
>             \framed{M}
>             \framed{\tfxx M}
>             \framed{\tfd M}
>         \stopTEXpage
>     \stoptext

  What are you trying to demonstrate with this?  If you change the size
of the font, obviously the glyphs have different sizes.  The initial
size at \starttext is 12pt, then \tfxx and \tfd change the sizes, to 8pt
and 20.736pt respectively.  Hence the former looks quite small in the
box, and the latter looks very large.  All that’s perfectly normal, and
since you’re not changing the font, or even the glyph, it’s not a good
illustration of the points raised in your initial email.

> The issue with units per em is something I didn’t understand.

  That’s irrelevant for you as a font user.  Don’t worry about it.



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