% This template avoids the scontents package, which is only available on relatively recent TeX distributions
\documentclass[varwidth=0.999\maxdimen, crop, border=5pt]{standalone}
% The upper limit value of 'varwidth' can be referenced by \hsize.
\newcommand*{\setTextWidthReference}{%
  \setlength{\textwidth}{345.0pt}% Same value when you use 'varwidth=true'.
  \setlength{\linewidth}{\textwidth}%
  \setlength{\columnwidth}{\textwidth}%
}

% Packages
\usepackage{amsmath}
\usepackage{amssymb}

% Blank formula checking
\usepackage{ifthen}
\newlength{\pheight}

% Color support
\usepackage{xcolor}
\definecolor{xpp_font_color}{HTML}{%%XPP_TEXT_COLOR%%}

% User input
\def\preview{\( 
    \displaystyle
    %%XPP_TOOL_INPUT%%
    \)%
}

\begin{document}
  \setTextWidthReference
  % Check if the formula is empty
  \settoheight{\pheight}{\preview}
  \ifthenelse{\pheight=0}{\GenericError{}{xournalpp:blankformula}{}{}}

  % Render the user input
  \textcolor{xpp_font_color}{\preview}
\end{document}