TL;DR: A list of use cases where using LuaTeX is more advantageous than using pdfTeX
------------ Many times Org users who frequently need to export their documents to LaTeX, but who do not have much LaTeX experience (or their knowledge of the TeX ecosystem is somewhat out of date), find themselves confused by the different versions of the TeX engine: pdfTeX, XeTeX, LuaTeX… In Org pdfTeX is the default engine, which in 2022 has a few limitations and is really old, but still perfectly meets the needs of a significant group of users. However, there may be a number of cases where it is more advantageous to compile with LuaTeX, so here I will leave a short list of those cases where LuaTeX may be a happy choice over pdfTeX. But first it is worth clarifying some things about LuaTeX along with some misunderstandings: • LuaTeX is the evolution of pdfTeX, therefore LuaTeX can be considered as the current de facto TeX engine. It is intended to replace pdfTeX, and in fact many of us already consider pdfTeX obsolete and deprecated. • To use LuaTeX it is not necessary to learn anything new or to know how to program in Lua. LuaTeX includes a Lua interpreter and the ability to bypass TeX primitives through Lua scripting (hence called LuaTeX). But all of that is more on the side of developers and packagers. For example, I am currently writing two LaTeX packages (one in collaboration with a colleague) where 80% of the code is Lua and 20% is (La)TeX. Of course, any user who knows Lua can take advantage of the \directlua primitive or the luacode environment in their documents. • A standard LaTeX document is always a LaTeX document, regardless of the flavor of TeX used to compile that document. There will be some minor differences. For example, in LuaLaTeX it is unnecessary to add fontenc and inputenc commands in the preamble. And now we go with the non-exhaustive list of cases where compiling with LuaTeX can be more advantageous for the user: 1. When you need to work in a *real* Unicode environment and not in pdfTeX’s 'fake Unicode'. And, especially, when it is required to work with languages that use a non-Latin writing system: Greek, Arabic, Hebrew, all the languages that use Cyrillic, oriental languages, etc. An extreme example you can see in this small code that I wrote for LuaTeX in order to be able to use the syllabograms of the ancient Mycenaean script: <https://gitlab.com/maciaschain/linealb-in-luatex> 2. When using truetype or opentype fonts is required. The pdfTeX user is limited to using only the included type1 fonts, the number of which is very limited. Besides, type1 is a deprecated and pre-unicode format. In fact, it almost always ends up leaving the default Computer Modern font. In LuaTeX we can use not only all the fonts installed on our system but also any font (just indicate the path), which is an important advantage over XeTeX. A basic command could be something like (loading the fontspec package): ┌──── │ \setmainfont{Palatino Linotype} └──── And with the latest versions of Babel we can associate fonts for different writing systems, without the need to change languages explicitly with a \selectlanguage. We can define all the font families we want or redefine the default families. For example, with this command I define the default monospaced font and request that it be scaled according to the height of the lowercase of the main font: ┌──── │ \setmonofont{Iosevka Fixed Curly}[Scale=MatchLowercase] └──── 3. When you need to take advantage, to a greater or lesser extent, of the opentype features of a font. For example, here we define the main font to use old style numbers: ┌──── │ \setmainfont{Palatino Linotype}[Numbers=Lowercase] └──── We can also load the otf tags directly: ┌──── │ \setmainfont{Palatino Linotype}[RawFeature=+onum] └──── The fontspec package for managing fonts in LuaTeX and XeTeX is very versatile and powerful. We can also associate a different font as italic for an already defined font family, use different optical resolutions of a font, etc. If what you are looking for is precise and absolute fine-tuning of the fonts used, of course LuaTeX is the ideal choice. 4. In general, when professional-level typographic fine-tuning is needed (and far superior to that offered by dtp programs like InDesign or QuarkXpress). For example, we can define on the fly new position opentype properties for a specific font, without having to edit the font. It is a non-destructive method that uses the fonts.handlers.otf.addfeature lua function. For example, we can define a new kerning value for the letters A and V. We’ll call it ’mykern’ ┌──── │ \directlua{ │ fonts.handlers.otf.addfeature │ { │ name ="mykern", │ type ="kern", │ data = │ { │ ["A"] = { ["V"] = 270 }, │ }} │ } │ │ \setmainfont{Linux Libertine O}[RawFeature=+mykern] └──── Here you can see a more bizarre and vandalistic example, where I have replaced the accent of the accented letters in Spanish with the image of a hammer :-) https://i.imgur.com/iixxJmx.png Here I have placed the image of a dancer on the tilde of the spanish letter ñ: https://i.imgur.com/oIZzpbJ.png (The process is simply to decompose the complex characters from the precombined form to their canonical decomposition: NFC > NFD, and then use a png image as a diacritic :-): \newunicodechar{^^^^0301}{\raisebox{1.2ex}{\includegraphics[width=.28em]{martillo.png}}} 1. Lastly, a lot of new (increasingly) LaTeX packages are written on top of the advanced features of LuaTeX and require LuaTeX. A very useful package, for example, is impnattypo, for post-production fine-tuning (<https://www.ctan.org/pkg/impnattypo>). Among the many features of impnattypo we have the ability to prevent lines from ending in single-letter words. It also highlights in draft mode, homeoarchy cases, which are typographically incorrect. An example in one of my recent works: <https://i.imgur.com/Kf8Oot0.png> Best regards, Juan Manuel
