% !TEX program = pdflatexmk
% !TEX parameter = -shell-escape
% https://wiki.physik.uzh.ch/cms/latex:feynman_file#method_1feynmp-auto
% https://www.overleaf.com/learn/latex/Feynman_diagrams#Other_packages_for_drawing_Feynman_diagrams
\documentclass[a4paper,12pt]{article}
\usepackage[margin=2.4cm]{geometry} % margins
\usepackage{amsmath}
\usepackage{graphicx}
\usepackage{feynmp}

% macro to compile Feynman graphs without extra scripts
\DeclareGraphicsRule{*}{mps}{*}{}
\makeatletter
\def\endfmffile{
  \fmfcmd{\p@rcent\space the end.^^J end.^^J endinput;}
  \if@fmfio
    \immediate\closeout\@outfmf
  \fi
  %\ifnum\pdfshellescape=\@ne
  \ifnum\pdfshellescape>\z@
    \immediate\write18{mpost \thefmffile}
  \fi}
\makeatother

\begin{document}

This is a test file for Feynman diagrams. You need to compile twice: once to compile and save the Feynman diagrams, twice to include them in the typeset PDF file.

\begin{figure}[h]
\vspace{10mm}
\centering
\begin{fmffile}{feynman-compton}
  \begin{fmfgraph*}(150,100)
    \fmfleft{i1,i2}
    \fmfright{o1,o2}
    \fmflabel{$\gamma$}{i2}
    \fmflabel{$e^-$}{i1}
    \fmflabel{$\gamma$}{o1}
    \fmflabel{$e^-$}{o2}
    \fmf{photon}{i2,v2}
    \fmf{fermion}{i1,v1,v2,o2}
    \fmf{photon}{v1,o1}
  \end{fmfgraph*}
\end{fmffile}
\vspace{5mm}
\caption{Feynman diagram for Compton scattering} %\label{compton}
\end{figure}

\end{document}