I'm sure those libraries are good, you just tend not to encounter stuff like that in programs written casually or by people who think performance really matters

I'm sure those libraries are good, you just tend not to encounter stuff like that in programs written casually or by people who think performance really matters. Most people doing triangulation by ear clipping are trying to rasterize shapes. In the past, cairo (the 2d graphics library) had a bug that would cause crashes/hangs in Firefox because a VPN driver was changing the floating point state on random threads... which would cause one of those geometric algorithms to break.