Text rendering is one of those things that someone thinks they can get a basic version running in a week or so and 5 months later they're still trying to address rendering/memory/performance issues for a production quality renderer(or something on a constrained platform). So much of text is just implicit knowledge and it's amazing much our brains "skip over".

I've written two of them "from scratch" professionally with many supporting libraries and both times they were pretty serious undertakings.