SDF ("Signed Distance Field") generation algorithms

Algorithms

Currently, this library contains these SDF generation algorithms:

• sdfer::bruteforce_bitmap: bitmap-based "closest opposite-color pixel" bruteforce search
  • this is the algorithm popularized by Valve in their 2007 SIGGRAPH submission, "Improved Alpha-Tested Magnification for Vector Textures and Special Effects"
  • prohibitively expensive, as the lack of precision (per pixel) leads to needing much larger input images (Valve paper gives 4096x4096 -> 64x64 as an example)
• sdfer::esdt: "Euclidean Subpixel Distance Transform"
  • this is a Rust port of the original JS implementation, from the @use-gpu/glyph npm package
  • the https://acko.net/blog/subpixel-distance-transform/ blog post explains how the older EDT ("Euclidean Distance Transform") algorithm was modified to better use the information present in e.g. grayscale AA rasterization of glyphs (where "grayscale AA" is really an alpha channel encoding of per-pixel coverage)
  • scales (roughly) linearly with the number of output pixels (which are 1:1 with input pixels, so no oversized rasterization required either), making it far more viable than most other algorithms, for on-demand runtime glyph->SDF conversion
    (e.g. to avoid pixel-snapping text during scrolling/panning, to allow some amount of smooth pinch-zooming before needing larger rasterizations, etc.)

<!-- FIXME(eddyb) write an explanation of pros-vs-cons, especially for ESDT -->

License

Licensed under the MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT).

_{Note: this is MIT-only, instead of the common dual-licensing, mainly due to the ESDT algorithm implementation being a port of the JS code from the @use-gpu/glyph npm package, which itself is MIT-licensed.}

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, shall be licensed as MIT, without any additional terms or conditions.