Function tri_normal

perro_source/render_stack/perro_meshlets/src/lib.rs:665–670

(vertices: &[LodVertex], tri: [u32; 3])

fn build_topology(vertices: &[LodVertex], triangles: &[[u32; 3]], scratch: &mut SimplifyScratch) {
    for (tri_index, tri) in triangles.iter().enumerate() {
        for (a, b) in [(tri[0], tri[1]), (tri[1], tri[2]), (tri[2], tri[0])] {
            let key = if a <= b { (a, b) } else { (b, a) };
            scratch
                .edges
                .entry(key)
                .and_modify(|edge: &mut EdgeInfo| edge.count = edge.count.saturating_add(1))
                .or_insert(EdgeInfo { count: 1 });
        }