ConTeXt: How to redefine the euro sign glyph?

Question

Introduction

I am writing a document using the TeX Gyre Pagella font. Unfortunately, the glyph for the euro sign (UTF-8 character U+20AC) in this font does not comply with the official euro sign specification.

Luckily, the Martin Vogel symbol font does contain a symbol which glyph seems alright.

Minimum working example

\setupbodyfontenvironment[default][em=italic]
\usemodule[simplefonts][size=14pt]
\setmainfontfallback[DejaVu Serif][range={greekandcoptic, greekextended}, force=yes, rscale=auto]
\setmainfont[TeX Gyre Pagella]

% Martin Vogel Symbol font for euro sign
\usesymbols[mvs]
%\definesymbol[€][{\symbol[europe][EUR]}]

\starttext
\startitemize[packed]
\item € is the glyph of the TeX Gyre Pagella font.
\item \symbol[europe][EUR]~is the glyph of the Martin Vogel symbol font.
\stopitemize
\stoptext

Question

How can I redefine the encoding for U+20AC (€) so that it corresponds to the Martin Vogel glyph?

In other words, I am looking for a preamble command so that the first line in the MWE also would show the Martin Vogel symbol glyph.

My commented-out \definesymbol[€] attempt did not work...

Answer 1

The problem is that the Martin Vogel font does not contain the Euro symbol in the correct slot, so you can't just use a simple font fallback as described in this answer. I don't know if there's a simple way to map a font fallback to different slots of another font without messing with virtual fonts.

Solution 1

Here is a simple workaround, which just replaces all occurences of “€” with an instruction to insert a particular glyph from another font. This is not very robust and might break unexpectedly (for instance in verbatim environments).

\usemodule [translate]
\enableinputtranslation

\translateinput
  [€]
  [\getnamedglyphdirect{marvosym.ttf}{EUR}]

\starttext
  €
\stoptext

Solution 2

Here's a second solution which is more robust than the crude input translation. It uses a regular font fallback and the new simplefonts module which is part of the core as of 2013.09.30 20:05. The euro sign is taken from the Martin Vogel font. Because the euro sign uses a wrong slot, a font feature is created using a substitution to correct the font slot. The euro sign is taken from the Martin Vogel font, although it does exist in the main font.

\startluacode
    fonts.handlers.otf.addfeature {
        name    = "euro",
        type    = "substitution",
        nocheck = true,
        data    = { [0x20AC] = "EUR" },
    }
\stopluacode

\definefontfeature
    [euro]
    [mode=node,
     euro=yes]

\definefallbackfamily [mainface] [serif] [MarVoSym] [range=0x20AC, features=euro, force=yes]
\definefontfamily     [mainface] [serif] [TeX Gyre Pagella]

\setupbodyfont [mainface]

\starttext
    The euro sign (€) is the currency sign used for the euro.
    In Unicode it is encoded at \type{U+20AC €} euro sign.
\stoptext