Migrating from XeTeX to LuaTeX

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In many languages and scripts, particularly Latin, Greek and Cyrillic, a document written for xetex should work with luatex without changes.

See also the companion guide Migrating from pdfTeX to LuaTeX if you are switching from pdfTeX.

It is worth noting that, contrary to what is sometimes assumed, the use of luatex does not require any programming knowledge in Lua (only certain advanced functions not available in other engines).

Fonts

By default, the font renderer in xetex is Harfbuzz (the only available). With luatex the default renderer was Node, but in version ≥24.14 is Harfbuzz, except scripts of the ‘Greek family’ (including Latin and Cyrillic). So, in versions ≤24.13 you may need to replace something like

\babelfont{rm}{FreeSerif}

with

\babelfont{rm}[Renderer=Harfbuzz]{FreeSerif}

RTL scripts

The xetex and luatex models are quite different (actually, xetex lacks a true RTL model). The main change is to replace the package option bidi=bidi with bidi=basic. If you were using bidi=default, no change is necessary.

Note xetex only ‘reverses’ the text, while luatex ‘reverses’ also margins, columns, and so on, so with these elements expect different results.

Mapping

This font feature is not available in luatex, but it can be replaced advantageously with transforms. There are already some transforms to transliterate a few languages. Native digits are already handled by babel out of the box.

In some cases, a better option are font features, but there aren’t available with Harfbuzz. (However, ‘constructors’ are, although they can be cumbersome.) As a reference, here are some basic patterns taken from luaotfload (lowercase means ‘from’ and uppercase ‘to’; note the ligature type is, in some sense, ‘reversed’). See sec. 15 in Font extensions for further info (focused on context, but pure Lua examples are valid in lualatex):

fonts.handlers.otf.addfeature {
    name = "stest",
    type = "substitution",
    data = {
        a = "X",
        b = "P",
    }
}
fonts.handlers.otf.addfeature {
    name = "mtest",
    type = "multiple",
    data = {
        a = { "X", "Y" },
        b = { "P", "Q" },
    }
}
fonts.handlers.otf.addfeature {
    name = "ltest",
    type = "ligature",
    data = {
        X = { "a", "b" },
        Y = { "d", "a" },
    }
}
fonts.handlers.otf.addfeature {
    name = "ktest",
    type = "kern",
    data = {
        a = { b = -500 },
    }
}

‘Interchar’ mechanism

It can be replaced with transforms, too.

The package ucharclasses can be replaced in most cases with the babel option onchar. The latter, unlike the former, works with RTL scripts.