It's also trickier to support Unicode and arbitrary fonts.
I was building a 3D game for language learning on mobile, and the font rendering in Unity3D was awful (blurry and rasterized).
When I eventually ended up writing my own engine, I started with bitmap fonts and quickly switched to SDF shaders. I ended up having to regenerate the texture on-the-fly as new characters were needed, acting as a cache (one of the markets was China -- you're not going to just stash all of the characters into one texture).
Another wrinkle: There's also right-to-left writing systems like Hebrew and Arabic, but those weren't our markets.
If you want languages with more interesting shaping, you have to start compositing glyphs; but good shapers are out there. HarfBuzz is amazing, I'm always amazed how well random bits of Farsi and Mongolian typeset on my systems.
Not sure about Unity, but it helps to be able to submit the geometry, the shader, and the uniforms, then asynchronously (or if you're lucky, in another thread) submit the SDF after you're done computing it.
With respect to slug, do you know if it would be usable with something like nerd fonts (custom glyphs)? My impression is yes, but I wasn't quite clear.
I was building a 3D game for language learning on mobile, and the font rendering in Unity3D was awful (blurry and rasterized).
When I eventually ended up writing my own engine, I started with bitmap fonts and quickly switched to SDF shaders. I ended up having to regenerate the texture on-the-fly as new characters were needed, acting as a cache (one of the markets was China -- you're not going to just stash all of the characters into one texture).
Another wrinkle: There's also right-to-left writing systems like Hebrew and Arabic, but those weren't our markets.
So far, the best I've seen is Eric Lengyel's Slug library: [1] http://sluglibrary.com/