expansion of tikz coordinates

Question

I trid to draw a line with TikZ and failed, as the code of version 1 shows. I think this is because the expression \pgfmathresult\textwidth for the end coodinate does not expand. So I tried the code of version 2 and version 3, attempting to expand \pgfmathresult\textwidth first. But both does not work either. Why?

Though the code of version 4 typesets the line as expected, I don't want to introduce an auxilary macro(here is \x).

So, how to expand an expression in coodinates in the scope of TikZ itself?

MWE:

\documentclass{article}
\usepackage{geometry,tikz}
\geometry{showframe}


\parindent0pt
\begin{document}
\pgfmathparse{0.1+0.2}\pgfmathresult

% Version 0:
V0: |\tikz\draw(0,0)--(\textwidth * \value{page} / 3,0);|

% Version 1: fail
V1: |\tikz\draw(0,0)--(\pgfmathresult\textwidth,0);|

% version 2: fail
V2: |\tikz\draw(0,0)--(\expanded{\pgfmathresult\textwidth},0);|

% version 3: fail
V3: |\tikz\draw(0,0)--(\the\dimexpr\textwidth * \pgfmathresult\relax,0);|

% version 4: works, but I don't want to introduce an new auxilary macro.
V4: |\edef\x{\noexpand\tikz\noexpand\draw(0,0)--(\pgfmathresult\textwidth,0);}\x|

\end{document}

Answer 1

Description

I suggest two easier approaches:

• V5: Use a variable to save the result and use it later (\let\mylinefactor\pgfmathresult). This also allows you to calculate multiple things with \pgfmathparse afterwards.
• V6: If you need the variable only once, you could put the calculation inside the tikz expression if you add \usetikzlibrary{calc}.

Code

\documentclass{article}
\usepackage{geometry,tikz}
\geometry{showframe}

\usetikzlibrary{calc}

\parindent0pt
\begin{document}
\pgfmathparse{0.1+0.2}\pgfmathresult
\let\mylinefactor\pgfmathresult % save the result

\pgfmathparse{0.2+0.3}\pgfmathresult % so you could make other calculations afterwards

% Version 0:
V0: |\tikz\draw(0,0)--(\textwidth * \value{page} / 3,0);|

% Version 5: works
V5: |\tikz\draw(0,0)--(\mylinefactor\textwidth,0);|

% Version 6: works
V6: |\tikz\draw(0,0)--({(0.1+0.2)*\textwidth},0);|

\end{document}

Result

Answer 2

Lines without tikz:

\documentclass{article}
\usepackage{showframe}
\usepackage{xfp}
\parindent0pt
\def\factor{\fpeval{0.1+0.2}}
\begin{document}
V7: |\rule{\dimexpr \textwidth * \value{page} / 3}{0.5pt}|

V8: |\rule{\dimexpr \factor\textwidth}{0.5pt}|
\end{document}