tabs.tex

\newcounter{row}

\def\changelettercatcodes{%
    \catcode`C=13
    \catcode`D=13
    \catcode`E=13
    \catcode`F=13
    \catcode`G=13
    \catcode`A=13
    \catcode`H=13
}

\def\changelettercatcodesback{%
    \catcode`C=11
    \catcode`D=11
    \catcode`E=11
    \catcode`F=11
    \catcode`G=11
    \catcode`A=11
    \catcode`H=11
}

\def\changecatcodes{%
    % Tunes, start of a string line
    \changelettercatcodes%
    %
    \catcode`X=13 % to show chords above
    %
    \catcode`\|=11
    \catcode`\~=11
    \catcode`\^^M=13 % newline
    \catcode`-=12
}

\def\charwidth{.65em} % width of each character in the tab

% print string tune letter
\gdef\tune#1{\raisebox{1pt}{\hbox to 10pt{\scriptsize#1\hss}}}
\gdef\notune#1{\raisebox{1pt}{\hbox to 10pt{}}}

\begingroup
\catcode`\|=11%
\catcode`\^^M=13% newline
\catcode`-=12%
\catcode`\ =12% change catcode of space to "other" to process them as characters. There can't be spaces in the following code.
\gdef\starttabchords#1^^M{\nopagebreak[4]\parindent=0pt%
\tokencycle%
{\addcytoks{\ifx-##1\phantom{\rule[.8ex]\charwidth{.5pt}}%
\else{\ifx##1|\makebar%
\else{\ifx ##1\makebox[\charwidth]{}% process space
%TODO: count characters and spaces, make letters (chords) large and before next non-space character fill the space with one box of a fitting size.
%TODO: don't require to start the chords with X
\else\makebox[\charwidth]{##1}\fi}%
\fi}\fi}}%
{\processtoks{##1}}%
{\addcytoks{##1}}%
{}% ignore spaces, space char now has catcode 12
#1\endtokencycle%
\catcode`\ =10\changelettercatcodes%
\newline}
\endgroup

\begingroup
\changecatcodes

\tracingmacros=1
\gdef\startstring#1^^M{\nopagebreak[4]\parindent=0pt%
    \tokencycle%
    {\addcytoks{\ifx-##1\rule[.8ex]\charwidth{.5pt}\else{%
    \ifx |##1\makebar\else{%
    \ifx ~##1{\raisebox{1.5pt}{\makebox[\charwidth]{\resizebox{.5em}{!}{$\sim$}\hfil}}}%
    \else\makebox[\charwidth]{##1}%
    \fi}\fi}\fi}}% apply above logic for char tokens (and those we declared char)
    {\processtoks{##1}}% group content processing directive
    {\addcytoks{##1}}% macro processing directive
    {}% space processing directive
    #1\endtokencycle%
    \stepcounter{row}\newline}

\gdefC{\tune{\string C}\startstring}
\gdefD{\tune{\string D}\startstring}
\gdefE{\tune{\string E}\startstring}
\gdefF{\tune{\string F}\startstring}
\gdefG{\tune{\string G}\startstring}
\gdefA{\tune{\string A}\startstring}
\gdefH{\tune{\string H}\startstring}
\gdefX{\catcode`\ =12\changelettercatcodesback\notune{\string X}\starttabchords}
\endgroup


% write bar
\gdef\makebar{%
    \ifnum\value{row}=0%
        \rule[.8ex]{.8pt}{0ex}%
    \else%
        \rule[.8ex]{.8pt}{12.5pt}%
    \fi}


% have to change catcodes before definition to avoid global redefinition
% of ~, | and -, and define them locally inside.
% (tune letters G, D, A, E etc. can be defined globally without possible clash)
\begingroup
\changecatcodes
\gdef\tabs#1{\pagebreak[1]%
    \sbox0{$a$}% to load amsfonts/umsa.fd prior to changing catcodes to active
    \begingroup%
    \changecatcodes%
    %
    \leftskip=#1%
    %
    \setcounter{row}{0}%
    %
    \leavevmode%
    %
    \parindent=0pt%
    \baselineskip=10pt%
    \lineskiplimit=-100pt%
    \lineskip=0pt%
    \noindent%
    \normalsize%
    %\def\par{\setcounter{row}{0}}%
}
\endgroup

\gdef\endtabs{\par\pagebreak[1]\endgroup\vskip-10pt}