Prevent LuaLaTeX from splitting umlauts

Question

Here's a minimal example:

\documentclass{minimal}
\usepackage{fontspec}\setmainfont{Cambria}
\begin{document}aöz\end{document}

Compiling this into a PDF using lualatex and extracting the text using pdftotext, I get the string aö z, that is:

U+0061(a) U+006f(o) U+0308(combining diaeresis) U+0020(space) U+007a(z)

Two problems with this: there's an unnecessary space (due to some PDF formatting trickery, the uncompressed datastream shows Tm[<…>125<01C5>-124<…>]TJ), and I don't want the umlaut to be split into base and combining character because for some reason that renders weirdly when changing the font size. I want the output to be

U+0061(a) U+00f6(ö) U+007a(z)

And the worst thing: with \setmainfont{Lucida Grande}, I get exactly that. Just not with Cambria.

Both are in TTF format. Checking the fonts in fontforge shows that both their U+00f6 glyphs are defined as composed of U+006f U+0308, only difference being that Cambria defines its OTF Class as “Base Glyph” while in Lucida Grande it's “Automatic” (no idea what that means).

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It is a fontspec specific problem:

\documentclass{minimal}
\usepackage{luaotfload}
\font\foo={name:Cambria} at 10pt
\begin{document}
aöz \foo aöz
\end{document}

generates what I expect, first umlaut missing as expected, too:

U+0061(a) U+007a(z) U+0020(space) U+0061(a) U+00f6(ö) U+007a(z)

but

\documentclass{minimal}
\usepackage{fontspec}
\begin{document}
aöz \fontspec{Cambria} aöz
\end{document}

generates

U+0061(a) U+00f6(ö) U+007a(z) U+0020 U+0061(a) U+006f(o) U+0308 U+0020 U+007a(z)

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Same when using \DeclareUTFcharacter{x00F6}{\foo} and replacing ö with \foo{}, so I guess it's not xunicode's fault?

Answer 1

From this answer I learned there is a Renderer=Basic option that causes an unknown number of side-effects.

\documentclass{minimal}
\usepackage{fontspec}
\defaultfontfeatures{Renderer=Basic}
\begin{document}
aöz \fontspec{Cambria} aöz ffi
\end{document}

The font doesn't seem to use ligatures anyway, where I want to use special features like VerticalPosition=Numerator for vulgar fractions, I can just switch to Renderer=Full.

A way to keep it from messing around in my unicode while keeping all functionality would be better though…

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I've been using the Basic renderer since and it seems to support the font's built in ligatures after all (for Cambria look at ti), no TeX-ligatures like --- for dashes though, need to enter those as unicode —