magic.sty

\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{magic}[2019/07/23]
\RequirePackage{kvoptions}      % option processing
\RequirePackage{geometry}       % for \geometry
\RequirePackage{etoolbox}       % for \ifdefstring, \ifdefvoid, etc.
\RequirePackage{xfp}            % for \fpeval

%% Options
\DeclareStringOption[3/4]{text}
\DeclareStringOption[4/5]{paper}
\DeclareStringOption[5/6]{hscale}
\DeclareStringOption[345pt]{width}
\DeclareStringOption[1]{scaled}

\ProcessLocalKeyvalOptions*

\newlength\magic@pw \newlength\magic@ph
\newlength\magic@tw \newlength\magic@th

\setlength\magic@tw{\magic@width}
\setlength\magic@tw{\fpeval{1/(\magic@scaled)}\magic@tw}
\setlength\magic@th{\fpeval{1/(\magic@text)}\magic@tw}
\setlength\magic@pw{\fpeval{1/(\magic@hscale)}\magic@tw}
\setlength\magic@ph{\fpeval{1/(\magic@paper)}\magic@pw}

\pagestyle{empty}
\geometry{
  papersize={\magic@pw,\magic@ph},
  total={\magic@tw,\magic@th},
  vratio={1:1}
}