Function simplify_surface

perro_source/render_stack/perro_meshlets/src/lib.rs:271–325

(vertices: &[LodVertex], surface_indices: &[u32], keep_tris: usize)

        vec![LodSurfaceRange {
            index_start: 0,
            index_count: indices.len() as u32,
        }]
    } else {
        surface_ranges.to_vec()
    };
    for range in &base_surfaces {
        let start = range.index_start as usize;
        let end = start.checked_add(range.index_count as usize).ok_or(
            MeshletBuildError::SurfaceRangeOutOfBounds {
                index_start: range.index_start,
                index_count: range.index_count,
                index_len: indices.len(),
            },
        )?;
        if end > indices.len() {
            return Err(MeshletBuildError::SurfaceRangeOutOfBounds {
                index_start: range.index_start,
                index_count: range.index_count,
                index_len: indices.len(),
            });
        }
    }

    let tri_count = indices.len() / 3;
    if tri_count == 0 || target_ratios.is_empty() {
        return Ok(vec![LodSet {
            indices: indices.to_vec(),
            surface_ranges: base_surfaces,
        }]);
    }

    let ratios = target_ratios
        .iter()
        .map(|ratio| {
            if ratio.is_finite() {
                ratio.clamp(0.0, 1.0)
            } else {
                1.0
            }
        })
        .collect::<Vec<_>>();
    let build_surface = |range: &LodSurfaceRange| {
        let start = range.index_start as usize;
        let end = start + range.index_count as usize;
        build_surface_lods(vertices, &indices[start..end], &ratios)
    };
    let per_surface_lods = if base_surfaces.len() >= 4 && tri_count >= 512 {
        base_surfaces
            .par_iter()
            .map(build_surface)
            .collect::<Vec<_>>()
    } else {
        base_surfaces.iter().map(build_surface).collect::<Vec<_>>()
    };

    let mut lods = Vec::new();
    for ratio_index in 0..ratios.len() {
        let mut lod_indices = Vec::new();