Access specific characters in LuaTeX

Question

Recently, I switched from XeTeX to LuaTex for a document of mine. However, there is a feature which I do not immediately see how to convert: Accessing specific characters. In particular, I need the upright double quote. In the font I use, however, the standard \dq command produces upper 99 quotes. In XeTeX, I therefore redefined the command:

\renewcommand\dq{\XeTeXglyph\XeTeXglyphindex"quotedbl"}

1. How can I do that in general, ie. how can I access all the glyphs in the font, whereever they might be placed (even without a codepoint, perhaps)?
2. Is there another way to access the upright double quote?

Answer 1

You should be able to enter any characters from your font directly into your source, just like in XeTeX. With respect to the double upright quote, you need to load the font without the [Ligatures=TeX] option (or if you want the most of the TeX replacements, but not the " replacement, you can specifically turn off the TeX quote replacement feature:)

\documentclass{article}
\usepackage{fontspec}
\setmainfont[Ligatures=TeX,RawFeature=-trep]{Linux Libertine O}
\begin{document}
"This is in upright quotes but will preserve e.g. --- replacement"

\addfontfeature{RawFeature=+trep}
"This has replaced quotes"

\addfontfeature{RawFeature=-trep;-tlig}
"This is in upright quotes and doesn't preserve e.g. --- replacement"
\end{document}

The raw features are described in the luaotfload manual; the rest is plain fontspec. The default behaviour (if you don't load a font explicitly) is to turn on both features so as to mimic standard TeX behaviour.

Answer 2

Assuming you are using luaotfload (which is true if you are using fontspec as well), you can use the lua function fonts.otf.char() which takes either glyph name or glyph index, e.g.:

\documentclass{article}
\usepackage{fontspec}
\setmainfont{TeX Gyre Pagella}

\def\fontchar#1{\directlua{fonts.otf.char("#1")}}
\def\dq{\fontchar{quotedbl}}

\begin{document}
\dq
\end{document}