Mark IV

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Revision as of 14:30, 6 August 2007 by Arthur (talk | contribs) (Corrected small mistakes; commented the LuaTeX code a bit.)
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Happy birthday M.!


Accelerate to Mark IV!

Today is the birth date of Mark IV, the coming of which we have been longing for since many years.

Life! Health! Prosperity!

Introducing Mark IV

Mark IV is the name of the LuaTeX-aware part of ConTeXt; that is, when you use ConTeXt over the LuaTeX engine instead of PDFTeX or XeTeX. You run it with texexec --lua.

The first public beta has been released on the 6th of August, 2007 and is readily available on ConTeXt Live. It takes advantage of the amazing capabilities of LuaTeX and opens up a whole new world of possibilities, in particular with fonts.

Sample code

Here are some examples of cool stuff you can do with Mark IV (test it!).

Lua core

The first thing you will want to test are the lua functions. Try

\ctxlua{a = 1.5 ; b = 1.8 ; c = a*b ; tex.print(c) ;}

or the equivalent:

a = 1.5
b = 1.8
c = a*b

You can also do more elaborate calculations with the lua math library:

\ctxlua{tex.print("$\string\\sqrt{2} = " .. math.sqrt(2) .. "$")}

Note that the above works with any flavour of LuaTeX; nothing is actually ConTeXt-specific (except for \ctxlua and \startlua/\stoplua).

Fonts and typescripts

Good ol' typescripts

Of course, Mark IV allows you to use typescripts as you've always done; for example:

effe fietsen 2: \input tufte $\sqrt{2}$ \eogonek

\sc effe fietsen 2: \input tufte $\sqrt{2}$ \eogonek

That's as simple as using a traditional ConTeXt typescript!

But ... how is it any different, then? Well, the difference is that in Mark IV, we can use an Opentype font directly, so that what is done here: when we want to use Palatino, the TeX Gyre equivalent (“Pagella”) is called and we can use its Opentype “features”; read on.

Opentype features

A “feature”, in the Opentype jargon, is a set of rules describing changes in the appearance of the text. Hmm, that's not very precise. Let's show some examples. First of all, you have to know that features are referred to by 4-letter tags, and you will see this a lot. One of them is ‘smcp‘, for “small caps“. Let's consider the following Mark IV-only code:

\palasmallcaps This is a text in small capitals.

Here you basically define a (Mark IV) feature with the name ”smallcaps”, and associate it with the (Opentype) feature “smcp”. You have to specify which script you want to use it with; scripts in Opentype are also tagged with four letters, and “latn” is of course Latin.

Then you define a TeX font with that feature.

You can see what features are defined in a particular font with the following bit of code

  fontname = 'texgyrepagella-regular.otf'

  --[[ First read the font data.
    This makes heavy use of some of the Mark IV code]]
  tfmdata = fonts.tfm.read_and_define("file:" .. fontname, 655360)
  font = tfmdata.shared.otfdata
  if font
    gsubfeatures = fonts.otf.analyze_features(font.gsub)
    gposfeatures = fonts.otf.analyze_features(font.gpos)

  if gsubfeatures then
    table.sort(gsubfeatures) % We want our list sorted alphabetically!
    tex.sprint("\\rm GSUB features: \\tt ") % Beware: you don't want \rm to be interpreted by lua (\rm would yield carriage return + letter m)!
    for _, feat in ipairs(gsubfeatures)
    do tex.sprint(feat) tex.sprint(' ')
  else tex.sprint("\\rm No GSUB features")

  if gposfeatures then
    tex.sprint("\\rm GPOS features: \\tt ")
    for _, feat in ipairs(gposfeatures)
    do tex.sprint(feat) tex.sprint(' ')
  else tex.sprint("\\rm No GPOS features")

It prints the list on the page. You'll notice there are two sets of features, each one of them defined in a different table of the Opentype font: the GSUB table (for Glyph SUBstitution) gives rules for replacing glyphs in certains circumstances (think of ligatures: f + i -> fi); the GPOS table (Glyph POSititioning) gives rules for moving glyphs (think of kerning: A + V -> A <kerning> V).

Incidentally, the above code gives some basic examples of LuaTeX programming, a mixture of both Lua and TeX programming with some special features (features in the general sense, not the Opentype one :-).