LuaLaTeX: Change kerning around "1" to simulate proportional figures

Question

I have the problem that both the original Helvetica and the Neue Helevetica font families by Linotype, in their OpenType versions, seem to not have proportional figures, only tabular figures, where each figure is monospaced. I tried switching to proportional figures with fontspec but it doesn't change the appearance a bit.

I need the proportional figures for paragraph text where tabular figures look weird. I find this situation pretty baffling, given that it seems to be a professional and well-known font. The tabular figures are most visible with the "1", which has too much space around it.

I found a possible solution inside LuaLaTeX with this answer: https://tex.stackexchange.com/a/323718/75284 but per David Carlisle's comment this approach would break numeric uses in other LaTeX commands. He mentions virtual fonts, how would one define a new virtual font and apply the needed kerning pairs?

Best would be a solution where one could define both generic kerning (left AND right) and define kerning pairs for fine tuning.

Please substitute Helvetica with a different font in your system if you don't have it.

% -*- program: lualatex  -*- 

\documentclass{article}
\usepackage{fontspec}

\defaultfontfeatures{Ligatures=TeX}

\setmainfont{HelveticaNeueLTStd-Roman}


\begin{document}
\obeylines

11111
88888

10 11 12 13 14 15 16 17 18 19 1.
01 11 21 31 41 51 61 71 81 91 .1

Desired output: 1\kern-.15em{1}

\end{document}

edit: follow-up question ragarding setting up both sides of a character to be kerned in LuaLaTeX: LuaLaTeX: fonts.handlers.otf.addfeature kerning pairs with unexpected behaviour

Answer 1

The code below using Arial rather than Helvetica produces the above.

The OP confirms that the code worked with teh Helvetica variant in the original question if

if(string.find(name,'HelveticaNeueLTStd'),

is used in place of

if(string.find(name,'arial')

If you switch \iffalse to \iftrue to use the modified font loader then you get the output below in which the typesetting of 1 has been changed in a subtle barely noticeable way.

\documentclass{article}

\usepackage{fontspec}

\iffalse

\directlua{
%
orig_define_font=luatexbase.remove_from_callback('define_font','luaotfload.define_font')
%
function x_define_font(name,size,id)
  local thisfont=orig_define_font(name,size,id)
  if(string.find(name,'arial') and type(thisfont)=='table') then
    thisfont.characters[49].width=thisfont.characters[49].width-200000
    thisfont.characters[49].commands = {
      {'right',-100000},
      {'special','pdf: 1 0 0 rg'},
      {'char',49},
      {'special','pdf: 0 g'},
      {'right',-100000},
    }
  end
  return thisfont
end
%
%
luatexbase.add_to_callback('define_font',x_define_font,'my_define_font')
%
}

\fi

\setmainfont{arial}

\begin{document}

abc 111 111 111 X

abc 123 111 222 X

abc 222 444 111 X

\end{document}

Answer 2

As you seem to want to adjust the spacing only if more numbers are involved, you could change the kernings between two numbers:

\documentclass{article}
\usepackage{fontspec}

\defaultfontfeatures{Ligatures=TeX}

\directlua
{
 fonts.handlers.otf.addfeature
  {
    name = "ktest",
    type = "kern",
    data =
        {
            ["1"] = { 
                      ["1"] =  -200 ,
                      ["2"] =  -200 
                    },
        },
  }
 }
\setmainfont{Arial}[RawFeature=+ktest]
\setsansfont{Arial} %to show the difference

\begin{document}
1111121212

\sffamily

1111121212

\end{document}

Answer 3

This doesn’t do it by adjusting the kerning, but if what you want are Helvetica-style proportional digits, an alternative approach is to substitute a font that has them, such as TeX Gyre Heros, and set the OpenType options to use them.

\documentclass[varwidth]{standalone}
\usepackage{fontspec}

\setsansfont{Arial}
\setmainfont{Arial}
\newfontfamily\pronums{TeX Gyre Heros}[Numbers={Lining,Proportional}, Scale=MatchUppercase]

\begin{document}
\fontsize{48}{48}
{\sffamily 111 222 333}

{\pronums 111 222 333}
\end{document}

If you want them in math mode, too, you can load that font for digits only in unicode-math.