The history of luaTEX 2006–2009 / v 0.50 - Pragma ADE

As you can see, it is possible to add alphabets, given that there is a suitable vector that
maps glyph indices onto Unicodes. It is good to know that this function only denes the
way such a font is constructed. The actual construction is delayed till the font is needed.
Such a virtual font is used in typescripts (the building blocks of typeface denitions in
ConTEXt) as follows:
\starttypescript [math] [palatino] [name]
\definefontsynonym [MathRoman] [pxmath@px-math]
\loadmapfile[original-youngryu-px.map]
\stoptypescript
If you're familiar with the way fonts are dened in ConTEXt, you will notice that we no
longer need to dene MathItalic, MathSymbol and additional symbol fonts. Of course
users don't have to deal with these issues themselves. The @ triggers the virtual font
builder.
You can imagine that in MkII switching to another font style or size involves initializing
(or at least checking) involves some 30 to 40 font denitions when it comes to math (the
number of used families times 3, the number o fmath sizes.). And even if we take into
account that fonts are loaded only once, this checking and enabling takes time. Keep in
mind that in ConTEXt we can have several math font sets active in one document which
comes at a price.
In MkIV we use one family (at three sizes). Of course we need to load the font (and more
than one in the case of virtual variants) but when switching bodyfont sizes we only need
to enable one (already dened) math font. And that really saves time. This is one of the
areas where we gain back time that we loose elsewhere by extending core functionality
using Lua (like OpenType support).
dimensions
By setting font related dimensions you can control the way TEX positions math elements
relative to each other. Math fonts have a few more dimensions than regular text fonts. But
OpenType math fonts like Cambria have quite some more. There is a nice booklet published
by Microsoft, ‘Mathematical Typesetting’, where dealing with math is discussed
in the perspective of their word processor and TEX. In the booklet some of the parameters
are discussed and since many of them are rather special it makes no sense (yet) to
elaborate on them here. 7 Figuring out their meaning was quite a challenge.
I am the rst to admit that the current code in MkIV that deals with math parameters is
somewhat messy. There are several reasons for this:
7
Googling on ‘Ulrich Vieth’, ‘TeX’ and ‘conferences’ might give you some hits on articles on these matters.
282 Unicode math