Valve originally devised this technique in 2007:

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

I originally had that near the top but in one of the rewrites I moved the papers to the end — https://www.redblobgames.com/articles/sdf-fonts/#appendix

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

Thanks!