Valve originally devised this technique in 2007:

https://steamcdn-a.akamaihd.net/apps/valve/2007/SIGGRAPH2007...

The article in question, https://www.redblobgames.com/articles/sdf-fonts/ is really neat as well, especially the interactive demonstrations

Oh thank-you for the reminder to check Amit's site again! (been following since the BBS and SolarRealms days...)