[dahart]

I used something close to this to implement a whiteboard marker with texture and transparency. If your browser supports WebGL, feel free to try https://limnu.com/d/new.html (BTW It’s a multi-player whiteboard you can share & collab.) Is that a shameless plug? I’m not involved anymore and won’t make any money, but I’m proud of the implementation, and happy if the current stewards of the site get some traffic or business.

Aside from that, for the sake of discussion and playing devil’s advocate I’ll take a small pedantic issue with the very first sentence. There are multiple ways to do this kind of thing without triangulating. (And I’m currently working on making one available publicly.) Clever shaders are one way to render lines without triangles. Ray tracing is another. Triangles are useful and easy and have broad support, so they make sense, but they aren’t the only option.