Add "Slug" for GPU-based Text Rendering

[andoowhy]

"Slug renders text and vector graphics on the GPU directly from Bézier curve data without the use of texture maps containing precomputed or cached images of any kind" -Eric Lengyel

Slug was under patent from 2019 through 2038, but Eric has graciously released his patent and given Slug to the public domain. He's also published Slug's "reference" pixel and vertex shaders at https://github.com/EricLengyel/Slug under a the permissive MIT license.

[IceSentry]

Are you having performance issues with text rendering in bevy? Also, even if there was performance issue, it's unclear if Slug would actually improve performance compared to alternative solutions.

[andoowhy]

Performance isn't my main reason for wanting Slug support. It's instead:

1. Super crisp glyph rendering at any zoom level, distance, or viewing angle
2. Doesn't rely on any pre-built or runtime-built SDF textures

[IceSentry]

Achieving this doesn't necessarily require Slug though. Feel free to open a PR of course, but it's hard to say if that's really the best solution for this.

[eira-fransham]

I agree that Slug would be really useful for some usecases, particularly text that exists in 3D space, but is there a reason that it should be upstreamed to Bevy? I feel like it’s a great candidate to be an ecosystem crate since it’s self-contained and serves a different purpose to regular text nodes, although if UI and 3D nodes get unified (which I believe might be planned) then there’s a stronger motivation to upstream it as an optional alternative rendering method for the built-in text component.

[IceSentry]

Yeah, this is the kind of thing that would benefit from being an ecosystem crate.

Also, it's debatable if Slug is actually the answer for those things. There are other ways to achieve these things with similar or better performance.

[yuanyan3060]

I have developed a Bevy plugin that implements this

https://github.com/yuanyan3060/bevy_slugtext
https://crates.io/crates/bevy_slugtext