% language=us runpath=texruns:manuals/ontarget

\startcomponent ontarget-bars

\usebodyfont[modern]
\usebodyfont[modern-nt]

\environment ontarget-style

\startchapter[title={Between bars}]

\startsubject[title=Inconsistencies]

The bar in math can a real pain. There are several reasons for this, for instance
there is no proper left, middle and right bar in \UNICODE\ and as a result there
is more work involved in getting them spaced well. Another possible issue can be
to make them fit well with other fences. You expect the bars in \im {\left(x
\middle| y\right)} and \im {\left|x \middle| y\right|} to look similar.

\start \glyphscale2000 \startformula
    \mathaxisbelow \dorecurse {\nofmathvariants \barasciicode} {
        \char \getmathvariant #1 \leftbracketasciicode
        \char \getmathvariant #1 \barasciicode
        \char \getmathvariant #1 \rightparentasciicode
        \quad
    }
\stopformula \stop

However, math fonts have their surprises:

\start \switchtobodyfont[modern-nt] \glyphscale2000 \startformula
    \mathaxisbelow \dorecurse {\nofmathvariants \barasciicode} {
        \char \getmathvariant #1 \leftbracketasciicode
        \char \getmathvariant #1 \barasciicode
        \char \getmathvariant #1 \rightparentasciicode
        \quad
    }
\stopformula \stop

In Latin Modern only the first variant is tuned to work together but for larger
sizes the bars stick out. This is a problem when we want fences to adapt. The
fact that such side effects probably get unnoticed comes from the fact that macro
packages assume \type {\bigg} and friends to be used but in \CONTEXT, and
especially \LMTX, we have various mechanisms for this. One method is based on
selecting specific variants, in the case of Latin Modern 1, 4, 6 and 7, where in
in fact 7 is the last one before we switch to extensible fences. One can try to
use a different selection for brackets and bars when there is no nice match but
there are no equal height matches.

\startbuffer
\im {\left| x       \right|}
\im {\left| x^2     \right|}
\im {\left| x^{1/n} \right|}
\stopbuffer

\typebuffer

These example formulas can trigger a larger fence:

\startlinecorrection \showglyphs
\ruledhbox{\scale[width=1tw]{\getbuffer}}
\stoplinecorrection

In untweaked Latin Modern we get this:

\startlinecorrection \switchtobodyfont[modern-nt] \showglyphs
\ruledhbox{\scale[width=1tw]{\getbuffer}}
\stoplinecorrection

The slash in this font is rather high and therefore triggers the larger fence.
One can configure this with the \typ {\delimiterfactor} and \typ
{\delimitershortfall} but as you can see values have to relate to the font. In
\LMTX\ we set them to 1000 and 0pt and use the \LUAMETATEX\ equivalent font
variables instead, so we can indeed fine tune per font.

To come back to the mismatch in fences, this is dealt with in a tweak: we scale
the single, double and triple bars to match the brackets:

\start \switchtobodyfont[modern] \startformula
    \mathaxisbelow \dorecurse {\nofmathvariants \barasciicode} {
        \char \getmathvariant #1 \leftbracketasciicode
        \char \getmathvariant #1 \barasciicode
        \char \getmathvariant #1 \rightparentasciicode
        \quad
    }
\stopformula \stop

Combined with proper settings for the factor (or percentage in \OPENTYPE\ math
speak) and shortfall, we now get:

\startlinecorrection \switchtobodyfont[modern] \showglyphs
\ruledhbox{\scale[width=1tw]{\getbuffer}}
\stoplinecorrection

When we let the upgraded math subsystem evolve we make many examples.
Unfortunately there is always an exception. For instance, we test a specific
font, notice something, deal with it, even test all fonts in inline and display
math and then after months the exception shows up. In this case it was the \im
{1/n} in a superscript that (only?) in Latin Modern goes over the top. Actually
we had noticed that bars are often inconsistent so we had a \type {fixbars}
tweak, However, for Latin Modern we found that the inconsistency between bars and
other fences needed something more drastic. Of course fixing the font is best but
we're beyond that stage now: the fonts are basically frozen.

A close inspection of the too large fence which itself results from it being
larger than expected by design (which we noticed by adding parentheses) itself
was the result from deciding to configure additional inter|-|atom spacing for
open and close fences (see below) which then brings us back to the fact that one
bar serves three purposes. We might actually introduce these three (left, middle
and right) at some point.

\startbuffer
\dm {\left| \frac{n^3 - 2n + 1}{n^5 - 3} - 0 \right| < \frac{4}{n^2} }
\stopbuffer

\startlinecorrection
\switchtobodyfont[modern]
\hbox{\scale[width=.45tw]{\getbuffer}\hskip .1tw
\inherited\setmathspacing\mathordinarycode\mathclosecode\allmathstyles\zeromuskip
\scale[width=.45tw]{\getbuffer}}
\stoplinecorrection

\stopsubject

\startsubject[title=Missing shapes]

The tweak discusses in the previous section is a brute force one: we put an
extensible on the base glyph. Among the arguments for doing this is that we want
to be able to add consistent double and triple bars. Without mentioning fonts
explicitly (as some might get fixed after we files bug reports) this is what
we observed:

\startitemize[packed]
\startitem
    There are single bars, double bars and triple bars and each has variants and
    extensibles. This is okay.
\stopitem
\startitem
    Most are there but the triple bar has no variants and extensibles
\stopitem
\startitem
    We have all three base characters but no variants. The extensible has a
    different width.
\stopitem
\startitem
    Single, double and triple bars are inconsistent with each other.
\stopitem
\startitem
    Everything is there but widths differ per variant; some match the parenthesis,
    brackets and braces but not consistently.
\stopitem
\startitem
    The different variant sizes are out of sync with the sizes of parenthesis
    etc.\ and this makes for inconsistent matches, especially when also the width
    and positioning differs.
\stopitem
\startitem
    Spacing between and around double and triple bars isn't always consistent.
\stopitem
\stopitemize

These observations lead us to the conclusion that there is no single tweak that
can fix this. Adapting the \quote {addbars} tweak to deal with all this made for
too many alternatives in checks and fixes to feel comfortable with. This is why
we decided to come up with companion fonts that provide the missing double and
triple variants and extensibles consistent with the single ones, fix spacing in
double and triple ones, fix inconsistent widths of bars, etc. Minor details like
bad positioning are already handled well do we can keep the \quote {design} as it
is.

\usebodyfont[pagella]

\start
\switchtobodyfont[pagella,15pt]
\dm{
  \dorecurse {\nofmathvariants "28} {
    \char \getmathvariant #1 "5B
    \char \getmathvariant #1 "7B
    \char \getmathvariant #1 "28
    \char \getmathvariant #1 "7C
    \char \getmathvariant #1 "29
    \char \getmathvariant #1 "7D
    \char \getmathvariant #1 "5D \quad }
}

\dm{
  \dorecurse {\nofmathvariants "7C} {
    \char \getmathvariant #1 "7C   \enspace
    \char \getmathvariant #1 "2016 \enspace
    \char \getmathvariant #1 "2980 \quad }
}
\stop

\stopsubject

\startsubject[title=Different sizes]

middle

\stopsubject

\stopchapter

\stopcomponent