Bevy Mikktspace

This is a rewrite of the Mikkelsen Tangent Space Algorithm reference implementation in Rust. It is loosely based on mikktspace, an existing port, except bevy_mikktspace has:

• exact byte-for-byte output equivalence with the original C source under all conditions[^1].
• fully idiomatic rust with no unsafe code, to support building in no-unsafe contexts.
• no dependencies, to avoid needing perpetual dependency-version-bump releases in the future.

Requires at least Rust 1.85.1.

Examples

cube_tangents

Demonstrates generating tangents for a cube with 4 triangular faces per side.

cargo run --example cube_tangents

Features

The original reference implementation has a couple bugs, which are largely inconsequential in most practical applications. However, fixing them would mean diverging from exact output equivalence, so bevy_mikktspace offers features to control this behavior:

• corrected-edge-sorting:

Correct a comparison in the reference's edge quicksort implementation. This can only differ on the last triangle in a model.

• corrected-vertex-welding:

Guarantees the smallest-index vertex is chosen when welding. This differs from the reference on NaN vertices.

License agreement

Licensed under either of

• Apache License, Version 2.0

(LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)

• MIT license

(LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option. AND parts of the code are licensed under:

• Zlib license

https://opensource.org/licenses/Zlib

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

[^1]: Extensive fuzz-testing against the reference implementation revealed divergence in NaN handling in https://github.com/gltf-rs/mikktspace, which is probably inconsequential for practical uses.