... where $DPI is either 120, 144, 75 or 96.
This files are static when system wide, but generated by Font Style
Manager in $FVWM_USERDIR.
Every X server's DPI state selects and reads one
of this files - the one which exactly or approximately matches current
DPI in this order:
if DPI is <= 85, $DPI is 75
if DPI is > 85 and < 108, $DPI is 96
if DPI is >= 108 and < 132, $DPI is 120
if DPI is >= 132, $DPI is 144
Font sizes in configs are defined as infostore variables and used across FVWM config files, an provided to FvwmScript programs with getfont wrapper. Font sizes are in points. While defining them in pixels (pixelsize=) will be easier, and all this care about DPI will not be needed, integration with GTK2 and GTK3 in best of my knowledge and research does not provide a way to define fonts in pixel sizes, so either font sizes in points or unsure recalculation (again based on DPI) will be needed while writing gtk settings.