Can TeX/LaTeX draw lines at precise positions?

Question

I need to draw lines at specific distances (in mm). For example:

---- line 0
---- line 1 at 35.64 mm below line 0
---- line 2 at 33.64 mm below line 1

The macro I'm using is as follows (I don't remember from where I copied it):

\def\fr#1{
  \vbox{  
    \dimen0=#1
    %\advance \dimen0 by -2.41pt
    \advance \dimen0 by -1pt
    \vskip \dimen0
    \vrule height 0.5pt depth 0.5pt width 2in
  }
}

And I use it as follows:

\parindent=0pt
\baselineskip=-\maxdimen
\lineskiplimit=\maxdimen
\lineskip=0pt


\#0 \fr{1mm}
\#1 \fr{35.64}
\#2 \fr{33.64}

However I cannot get the lines to appear at the desired positions.

Answer 1

This should be a matter of \vrule and \vskip only. The following should work:

\def\fr#1#2{\vskip #2\noindent\smash{#1}%
  \vrule height 0.4pt depth 0pt width 2in\relax}

\fr{0}{0mm}
\fr{1}{35.64mm}
\fr{2}{33.64mm}

\bye

Note how the \smash macro is used to prevent the numbers from adding any height or depth.

Answer 2

A Plain solution (inspired by Andrey's one):

\def\fr#1#2{\vskip #2\smash{#1 \vrule height 0.4pt depth 0pt width 2in}}

\offinterlineskip

% A ruler in the margin to show alignment
\llap{\smash{\vtop to 100pt{
  \leaders\vbox to 20pt{\leaders\vrule\vfill\hrule width 2mm}\vfill}}}

\fr{0}{20pt}
\fr{y}{40pt}
\fr{2}{20pt}

\bye