Re: towards a 'normal' Emmentaler font

[Werner LEMBERG]

> While playing around with accidentals, I compared Bravura's glyph
> metrics with the ones from Emmentaler.  In short: Bravura looks like
> a 'normal' font, while Emmentaler is non-standard.

Meanwhile I came to the conclusion that this doesn't matter because...

> With 'normal' I mean that if you mix Bravura glyphs with other text,
> they behave as expected, that is, the current position on the line
> gets increased similarly to other glyphs like 'a' or 'x'.

... after re-reading the SMuFL standard I found out that this isn't
true for Bravura either.

> I want to improve the situation eventually; I think the goal should
> be to make Emmentaler glyphs have similar bounding boxes as Bravura
> (and probably all other music notation fonts not designed for
> LilyPond).

Again, I convinced myself that this isn't necessary since...

> The solution on the font side is very simple: Move all glyphs to the
> right so that 'bp' becomes zero.  This automatically gives all
> glyphs the correct advance width.  The necessary changes on the
> METAFONT side are just a few lines of code.

... there is a much cleaner solution: Provide a completely different
set of metrics to create a text version of the Emmentaler fonts:
'Emmentaler Text', similar to 'Bravura Text'.

> [Note that the DVI proof sheet output would stay as-is; the horizontal
>  shift happens at glyph shipout time, which comes later.]

I now envision an additional macro `set_textchar_box`, to be inserted
right after `set_char_box`.

```
  set_textchar_box (<scale>, <left sidebearing>, <right sidebearing>);
```

If the global METAFONT parameter `text_metrics` is set to value 1, it
would do the following.

(1) Shift the glyph and its bounding box horizontally to the right by
    the value of the 'breapth' parameter given in `set_char_box`.

(2) Apply <left sidebearing> and <right sidebearings>, where <left
    sidebearing> shifts the glyph further to the right (so that the
    left side of the bounding box is positioned at x=0), and <right
    sidebearing> further extends the right side of the bounding box.

(3) Scale the glyph by <scale> to make it look good if typeset as
    text.

(4) In DVI proof mode, draw the new bounding box in stead of the old
    one.

Note that the goal is *not* to emulate what 'Bravura Text' is doing –
for example, it contains a poor-man's method to typeset small music
snippets with textglyphs (see
https://github.com/steinbergmedia/bravura/blob/master/redist/bravura-text.md
for more details); this is something that `lilypond-book` can do much
better.  The idea is rather to make the use of `\markup` easier by
entering Emmentaler glyphs without the need to apply `\hspace`,
`\magnify`, and other commands excessively; it would also help
packages like 'lilyglyphs' (for LaTeX) work better.

On the technical level, the Emmentaler fonts would become OpenType
Collections (which don't get the expected extension `.otc` but `.ttc`
for various reasons), containing both 'Emmentaler' and 'Emmentaler
Text' (compare this to the MS font `cambria.ttc`).  The glyphs with
new metrics would be composite glyphs that simply reference the glyphs
with the default metrics; this means that the size increase of the
font would be just a few kByte.

We would further need to implement WOFF2 support since neither WOFF
nor SVG support OpenType Collections.


    Werner