Problem changing fancyvrb’s default font

fancyvrbfonts

I would like to change the default font for fancyvrb in the following MWE.

    % arara: xelatex: { shell: true }
    \documentclass{article}
    \usepackage[svgnames]{xcolor}
    \usepackage{fontspec}
    \usepackage{fancyvrb}
    
    \newfontface{\cBld}{SourceSansPro-Bold.ttf}
    \newfontface{\cEm}{SourceSansPro-LightItalic.ttf}
    \newfontface{\cNrm}{SourceSansPro-Regular.ttf}
    
    \def\It#1{{\cEm #1}}
    \def\Bf#1{{\cBld #1}}
    \def\Br#1{{\color{IndianRed}{\cNrm #1}}}
    \def\Bl#1{{\color{CornflowerBlue}{\cNrm #1}}}
    \def\Gr#1{{\color{LimeGreen}{\cNrm #1}}}
    
    \begin{document}
    \begin{Verbatim}[commandchars=\\\{\}, numbers=left]
    \It{;;}
    \It{;; goff.ufm}
    \It{;; 13:00:35 11:08:2021 (MST)}
    \It{;;}
    MyGoFF \{
    \Bf{init:}
      z = \Br{@Z}
      \Bf{complex} zf = \Br{@ZF}
    
    \Bf{loop}:
      \Bf{if} \Br{@fof} > 0
        zf = Utils.\Bl{fofz}(\Br{@inverse}, \Br{@fof}, Utils.\Bl{zFunction}(\Br{@inverse}, \Br{@fofz},  z, \Gr{\#pixel}))
        z  = Utils.\Bl{fofz}(\Br{@inverse}, \Br{@fof}, Utils.\Bl{gFunction}(\Br{@inverse}, \Br{@gofz}, zf, \Gr{\#pixel}))
      \Bf{else}
        zf = Utils.\Bl{zFunction}(\Br{@inverse}, \Br{@fofz},  z, \Gr{\#pixel})
        z  = Utils.\Bl{gFunction}(\Br{@inverse}, \Br{@gofz}, zf, \Gr{\#pixel})
      \Bf{endif}
      \Bf{if} \Br{@const} > \Bl{0}
        \Bf{if} \Br{@op} == \Bl{0}
          z = z * Utils.\Bl{GetConstant}(\Br{@const});
        \Bf{elseif} \Br{@op} == \Bl{1}
          z = Utils.\Bl{GetConstant}(\Br{@const}) / z;
        \Bf{elseif} \Br{@op} == \Bl{2}
          z = z + Utils.\Bl{GetConstant}(\Br{@const});
        \Bf{elseif} \Br{@op} == \Bl{3}
          z = Utils.\Bl{GetConstant}(\Br{@const}) - z;
        \Bf{elseif} \Br{@op} == \Bl{4}
          z = z / Utils.\Bl{GetConstant}(\Br{@const});
        \Bf{elseif} \Br{@op} == \Bl{5}
          z = z - Utils.\Bl{GetConstant}(\Br{@const});
        \Bf{elseif} \Br{@op} == \Bl{6}
          z = z\^{}\Bl{2} + Utils.\Bl{GetConstant}(\Br{@const});
        \Bf{elseif} \Br{@op} == \Bl{7}
          z = z\^{}\Bl{2} - Utils.\Bl{GetConstant}(\Br{@const});
        \Bf{endif}
      \Bf{endif}
    \end{Verbatim}
    \end{document}

I have tried every work-around I could come up with but cannot get fancyvrb to use any thing but it's hard coded default or alternatives it provided for. The manual says that:

4.1.5 
Fonts fontfamily (family name) : font family to use. tt, courier and
helvetica are predefined (Default: tt).

I have tried helvetica, but then I run into the problem of differing character sizes of one font versus another. I want to use SourceSansPro-Regular.ttf but have not determined how. In my attempts, I have tried all variants of the fonts name:

    Family:              Source Sans Pro
    Subfamily:           Regular
    Full name:           Source Sans Pro Regular
    PostScript name:     SourceSansPro-Regular

None of these make the slightest difference. I believe the clue lies in the word 'predefined.' I did not see any API to accomplish this—the methods given did not effect any change.

If I could change the font, everything else works the way I want it. This is an effort to prototype a semi-'listings' environment. The language (Ultra Fractal's formula language) in question fits no parser otherwise available.

I'm using MikTeX 2.9 under Windows 11 (bleeding edge), the font family is available at https://fonts.google.com/specimen/Source+Sans+Pro

Best Answer

This is described in the fontspec documentation in 4.2 Specifically choosing the NFSS family:

\documentclass{article}
\usepackage{fontspec}
\usepackage{fancyvrb}
   
\newfontfamily\verbatimfont{SourceSansPro-Regular.ttf}[NFSSFamily=myverbatimfont]
    

\begin{document}
\begin{Verbatim}[fontfamily=myverbatimfont]
aaaa
\end{Verbatim}
\end{document}
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