Function build_topology

perro_source/render_stack/perro_meshlets/src/lib.rs:424–448

(vertices: &[LodVertex], triangles: &[[u32; 3]], scratch: &mut SimplifyScratch)

    let mut lods = Vec::with_capacity(ratios.len());
    for &ratio in ratios {
        let target = ((original_tri_count as f32) * ratio).ceil() as usize;
        let target = target.clamp(1, original_tri_count);
        let current_tris = current.len() / 3;
        if target < current_tris {
            current = simplify_surface(vertices, &current, target);
        }
        lods.push(current.clone());
    }
    lods
}

fn simplify_surface(vertices: &[LodVertex], surface_indices: &[u32], keep_tris: usize) -> Vec<u32> {
    let tri_count = surface_indices.len() / 3;
    let source = &surface_indices[..tri_count * 3];
    if keep_tris >= tri_count || tri_count == 0 {
        return source.to_vec();
    }
    if source.iter().any(|&idx| idx as usize >= vertices.len()) {
        return source.to_vec();
    }
    let mut triangles = source
        .chunks_exact(3)
        .map(|tri| [tri[0], tri[1], tri[2]])
        .filter(|tri| !tri_degenerate(*tri))
        .collect::<Vec<_>>();
    if triangles.len() <= keep_tris {
        return flatten_tris(&triangles);
    }