ref: 1d9c69e0ff3b386a33ed87da12286bbff3285caf
parent: 126bee7e131e05f58130d59a21a33b065fc8fe45
author: Sigrid Solveig Haflínudóttir <sigrid@ftrv.se>
date: Sat Oct 14 22:10:25 EDT 2023
make particles smaller by default, provide r_part_scale to customize