oxihuman-mesh 0.2.1

// Copyright (C) 2026 COOLJAPAN OU (Team KitaSan)
// SPDX-License-Identifier: Apache-2.0

use crate::mesh::MeshBuffers;
use crate::normals::compute_normals;

// ── Marching Cubes lookup tables ─────────────────────────────────────────────
//
// Corner numbering (standard Marching Cubes):
//
//     4---5
//    /|  /|
//   7---6 |
//   | 0-|-1
//   |/  |/
//   3---2
//
// Corner positions relative to cube min:
//   0: (0,0,0)  1: (1,0,0)  2: (1,1,0)  3: (0,1,0)
//   4: (0,0,1)  5: (1,0,1)  6: (1,1,1)  7: (0,1,1)
//
// Edge connections:
//   0: 0-1   1: 1-2   2: 2-3   3: 3-0
//   4: 4-5   5: 5-6   6: 6-7   7: 7-4
//   8: 0-4   9: 1-5  10: 2-6  11: 3-7

/// For each of the 256 cases, a bitmask of the 12 edges that are cut.
#[allow(dead_code)]
const EDGE_TABLE: [u16; 256] = [
    0x000, 0x109, 0x203, 0x30a, 0x406, 0x50f, 0x605, 0x70c, 0x80c, 0x905, 0xa0f, 0xb06, 0xc0a,
    0xd03, 0xe09, 0xf00, 0x190, 0x099, 0x393, 0x29a, 0x596, 0x49f, 0x795, 0x69c, 0x99c, 0x895,
    0xb9f, 0xa96, 0xd9a, 0xc93, 0xf99, 0xe90, 0x230, 0x339, 0x033, 0x13a, 0x636, 0x73f, 0x435,
    0x53c, 0xa3c, 0xb35, 0x83f, 0x936, 0xe3a, 0xf33, 0xc39, 0xd30, 0x3a0, 0x2a9, 0x1a3, 0x0aa,
    0x7a6, 0x6af, 0x5a5, 0x4ac, 0xbac, 0xaa5, 0x9af, 0x8a6, 0xfaa, 0xea3, 0xda9, 0xca0, 0x460,
    0x569, 0x663, 0x76a, 0x066, 0x16f, 0x265, 0x36c, 0xc6c, 0xd65, 0xe6f, 0xf66, 0x86a, 0x963,
    0xa69, 0xb60, 0x5f0, 0x4f9, 0x7f3, 0x6fa, 0x1f6, 0x0ff, 0x3f5, 0x2fc, 0xdfc, 0xcf5, 0xfff,
    0xef6, 0x9fa, 0x8f3, 0xbf9, 0xaf0, 0x650, 0x759, 0x453, 0x55a, 0x256, 0x35f, 0x055, 0x15c,
    0xe5c, 0xf55, 0xc5f, 0xd56, 0xa5a, 0xb53, 0x859, 0x950, 0x7c0, 0x6c9, 0x5c3, 0x4ca, 0x3c6,
    0x2cf, 0x1c5, 0x0cc, 0xfcc, 0xec5, 0xdcf, 0xcc6, 0xbca, 0xac3, 0x9c9, 0x8c0, 0x8c0, 0x9c9,
    0xac3, 0xbca, 0xcc6, 0xdcf, 0xec5, 0xfcc, 0x0cc, 0x1c5, 0x2cf, 0x3c6, 0x4ca, 0x5c3, 0x6c9,
    0x7c0, 0x950, 0x859, 0xb53, 0xa5a, 0xd56, 0xc5f, 0xf55, 0xe5c, 0x15c, 0x055, 0x35f, 0x256,
    0x55a, 0x453, 0x759, 0x650, 0xaf0, 0xbf9, 0x8f3, 0x9fa, 0xef6, 0xfff, 0xcf5, 0xdfc, 0x2fc,
    0x3f5, 0x0ff, 0x1f6, 0x6fa, 0x7f3, 0x4f9, 0x5f0, 0xb60, 0xa69, 0x963, 0x86a, 0xf66, 0xe6f,
    0xd65, 0xc6c, 0x36c, 0x265, 0x16f, 0x066, 0x76a, 0x663, 0x569, 0x460, 0xca0, 0xda9, 0xea3,
    0xfaa, 0x8a6, 0x9af, 0xaa5, 0xbac, 0x4ac, 0x5a5, 0x6af, 0x7a6, 0x0aa, 0x1a3, 0x2a9, 0x3a0,
    0xd30, 0xc39, 0xf33, 0xe3a, 0x936, 0x83f, 0xb35, 0xa3c, 0x53c, 0x435, 0x73f, 0x636, 0x13a,
    0x033, 0x339, 0x230, 0xe90, 0xf99, 0xc93, 0xd9a, 0xa96, 0xb9f, 0x895, 0x99c, 0x69c, 0x795,
    0x49f, 0x596, 0x29a, 0x393, 0x099, 0x190, 0xf00, 0xe09, 0xd03, 0xc0a, 0xb06, 0xa0f, 0x905,
    0x80c, 0x70c, 0x605, 0x50f, 0x406, 0x30a, 0x203, 0x109, 0x000,
];

/// Triangle table: for each of the 256 cases, up to 5 triangles
/// (3 edge indices each), terminated by -1.  Total: 256 × 16 entries.
#[allow(dead_code)]
const TRI_TABLE: [[i8; 16]; 256] = [
    [
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    ],
    [0, 8, 3, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [0, 1, 9, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [1, 8, 3, 9, 8, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [1, 2, 10, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [0, 8, 3, 1, 2, 10, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [9, 2, 10, 0, 2, 9, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [2, 8, 3, 2, 10, 8, 10, 9, 8, -1, -1, -1, -1, -1, -1, -1],
    [3, 11, 2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [0, 11, 2, 8, 11, 0, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [1, 9, 0, 2, 3, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [1, 11, 2, 1, 9, 11, 9, 8, 11, -1, -1, -1, -1, -1, -1, -1],
    [3, 10, 1, 11, 10, 3, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [0, 10, 1, 0, 8, 10, 8, 11, 10, -1, -1, -1, -1, -1, -1, -1],
    [3, 9, 0, 3, 11, 9, 11, 10, 9, -1, -1, -1, -1, -1, -1, -1],
    [9, 8, 10, 10, 8, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [4, 7, 8, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [4, 3, 0, 7, 3, 4, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [0, 1, 9, 8, 4, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [4, 1, 9, 4, 7, 1, 7, 3, 1, -1, -1, -1, -1, -1, -1, -1],
    [1, 2, 10, 8, 4, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [3, 4, 7, 3, 0, 4, 1, 2, 10, -1, -1, -1, -1, -1, -1, -1],
    [9, 2, 10, 9, 0, 2, 8, 4, 7, -1, -1, -1, -1, -1, -1, -1],
    [2, 10, 9, 2, 9, 7, 2, 7, 3, 7, 9, 4, -1, -1, -1, -1],
    [8, 4, 7, 3, 11, 2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [11, 4, 7, 11, 2, 4, 2, 0, 4, -1, -1, -1, -1, -1, -1, -1],
    [9, 0, 1, 8, 4, 7, 2, 3, 11, -1, -1, -1, -1, -1, -1, -1],
    [4, 7, 11, 9, 4, 11, 9, 11, 2, 9, 2, 1, -1, -1, -1, -1],
    [3, 10, 1, 3, 11, 10, 7, 8, 4, -1, -1, -1, -1, -1, -1, -1],
    [1, 11, 10, 1, 4, 11, 1, 0, 4, 7, 11, 4, -1, -1, -1, -1],
    [4, 7, 8, 9, 0, 11, 9, 11, 10, 11, 0, 3, -1, -1, -1, -1],
    [4, 7, 11, 4, 11, 9, 9, 11, 10, -1, -1, -1, -1, -1, -1, -1],
    [9, 5, 4, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [9, 5, 4, 0, 8, 3, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [0, 5, 4, 1, 5, 0, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [8, 5, 4, 8, 3, 5, 3, 1, 5, -1, -1, -1, -1, -1, -1, -1],
    [1, 2, 10, 9, 5, 4, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [3, 0, 8, 1, 2, 10, 4, 9, 5, -1, -1, -1, -1, -1, -1, -1],
    [5, 2, 10, 5, 4, 2, 4, 0, 2, -1, -1, -1, -1, -1, -1, -1],
    [2, 10, 5, 3, 2, 5, 3, 5, 4, 3, 4, 8, -1, -1, -1, -1],
    [9, 5, 4, 2, 3, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [0, 11, 2, 0, 8, 11, 4, 9, 5, -1, -1, -1, -1, -1, -1, -1],
    [0, 5, 4, 0, 1, 5, 2, 3, 11, -1, -1, -1, -1, -1, -1, -1],
    [2, 1, 5, 2, 5, 8, 2, 8, 11, 4, 8, 5, -1, -1, -1, -1],
    [10, 3, 11, 10, 1, 3, 9, 5, 4, -1, -1, -1, -1, -1, -1, -1],
    [4, 9, 5, 0, 8, 1, 8, 10, 1, 8, 11, 10, -1, -1, -1, -1],
    [5, 4, 0, 5, 0, 11, 5, 11, 10, 11, 0, 3, -1, -1, -1, -1],
    [5, 4, 8, 5, 8, 10, 10, 8, 11, -1, -1, -1, -1, -1, -1, -1],
    [9, 7, 8, 5, 7, 9, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [9, 3, 0, 9, 5, 3, 5, 7, 3, -1, -1, -1, -1, -1, -1, -1],
    [0, 7, 8, 0, 1, 7, 1, 5, 7, -1, -1, -1, -1, -1, -1, -1],
    [1, 5, 3, 3, 5, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [9, 7, 8, 9, 5, 7, 10, 1, 2, -1, -1, -1, -1, -1, -1, -1],
    [10, 1, 2, 9, 5, 0, 5, 3, 0, 5, 7, 3, -1, -1, -1, -1],
    [8, 0, 2, 8, 2, 5, 8, 5, 7, 10, 5, 2, -1, -1, -1, -1],
    [2, 10, 5, 2, 5, 3, 3, 5, 7, -1, -1, -1, -1, -1, -1, -1],
    [7, 9, 5, 7, 8, 9, 3, 11, 2, -1, -1, -1, -1, -1, -1, -1],
    [9, 5, 7, 9, 7, 2, 9, 2, 0, 2, 7, 11, -1, -1, -1, -1],
    [2, 3, 11, 0, 1, 8, 1, 7, 8, 1, 5, 7, -1, -1, -1, -1],
    [11, 2, 1, 11, 1, 7, 7, 1, 5, -1, -1, -1, -1, -1, -1, -1],
    [9, 5, 8, 8, 5, 7, 10, 1, 3, 10, 3, 11, -1, -1, -1, -1],
    [5, 7, 0, 5, 0, 9, 7, 11, 0, 1, 0, 10, 11, 10, 0, -1],
    [11, 10, 0, 11, 0, 3, 10, 5, 0, 8, 0, 7, 5, 7, 0, -1],
    [11, 10, 5, 7, 11, 5, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [10, 6, 5, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [0, 8, 3, 5, 10, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [9, 0, 1, 5, 10, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [1, 8, 3, 1, 9, 8, 5, 10, 6, -1, -1, -1, -1, -1, -1, -1],
    [1, 6, 5, 2, 6, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [1, 6, 5, 1, 2, 6, 3, 0, 8, -1, -1, -1, -1, -1, -1, -1],
    [9, 6, 5, 9, 0, 6, 0, 2, 6, -1, -1, -1, -1, -1, -1, -1],
    [5, 9, 8, 5, 8, 2, 5, 2, 6, 3, 2, 8, -1, -1, -1, -1],
    [2, 3, 11, 10, 6, 5, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [11, 0, 8, 11, 2, 0, 10, 6, 5, -1, -1, -1, -1, -1, -1, -1],
    [0, 1, 9, 2, 3, 11, 5, 10, 6, -1, -1, -1, -1, -1, -1, -1],
    [5, 10, 6, 1, 9, 2, 9, 11, 2, 9, 8, 11, -1, -1, -1, -1],
    [6, 3, 11, 6, 5, 3, 5, 1, 3, -1, -1, -1, -1, -1, -1, -1],
    [0, 8, 11, 0, 11, 5, 0, 5, 1, 5, 11, 6, -1, -1, -1, -1],
    [3, 11, 6, 0, 3, 6, 0, 6, 5, 0, 5, 9, -1, -1, -1, -1],
    [6, 5, 9, 6, 9, 11, 11, 9, 8, -1, -1, -1, -1, -1, -1, -1],
    [5, 10, 6, 4, 7, 8, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [4, 3, 0, 4, 7, 3, 6, 5, 10, -1, -1, -1, -1, -1, -1, -1],
    [1, 9, 0, 5, 10, 6, 8, 4, 7, -1, -1, -1, -1, -1, -1, -1],
    [10, 6, 5, 1, 9, 7, 1, 7, 3, 7, 9, 4, -1, -1, -1, -1],
    [6, 1, 2, 6, 5, 1, 4, 7, 8, -1, -1, -1, -1, -1, -1, -1],
    [1, 2, 5, 5, 2, 6, 3, 0, 4, 3, 4, 7, -1, -1, -1, -1],
    [8, 4, 7, 9, 0, 5, 0, 6, 5, 0, 2, 6, -1, -1, -1, -1],
    [7, 3, 9, 7, 9, 4, 3, 2, 9, 5, 9, 6, 2, 6, 9, -1],
    [3, 11, 2, 7, 8, 4, 10, 6, 5, -1, -1, -1, -1, -1, -1, -1],
    [5, 10, 6, 4, 7, 2, 4, 2, 0, 2, 7, 11, -1, -1, -1, -1],
    [0, 1, 9, 4, 7, 8, 2, 3, 11, 5, 10, 6, -1, -1, -1, -1],
    [9, 2, 1, 9, 11, 2, 9, 4, 11, 7, 11, 4, 5, 10, 6, -1],
    [8, 4, 7, 3, 11, 5, 3, 5, 1, 5, 11, 6, -1, -1, -1, -1],
    [5, 1, 11, 5, 11, 6, 1, 0, 11, 7, 11, 4, 0, 4, 11, -1],
    [0, 5, 9, 0, 6, 5, 0, 3, 6, 11, 6, 3, 8, 4, 7, -1],
    [6, 5, 9, 6, 9, 11, 4, 7, 9, 7, 11, 9, -1, -1, -1, -1],
    [10, 4, 9, 6, 4, 10, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [4, 10, 6, 4, 9, 10, 0, 8, 3, -1, -1, -1, -1, -1, -1, -1],
    [10, 0, 1, 10, 6, 0, 6, 4, 0, -1, -1, -1, -1, -1, -1, -1],
    [8, 3, 1, 8, 1, 6, 8, 6, 4, 6, 1, 10, -1, -1, -1, -1],
    [1, 4, 9, 1, 2, 4, 2, 6, 4, -1, -1, -1, -1, -1, -1, -1],
    [3, 0, 8, 1, 2, 9, 2, 4, 9, 2, 6, 4, -1, -1, -1, -1],
    [0, 2, 4, 4, 2, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [8, 3, 2, 8, 2, 4, 4, 2, 6, -1, -1, -1, -1, -1, -1, -1],
    [10, 4, 9, 10, 6, 4, 11, 2, 3, -1, -1, -1, -1, -1, -1, -1],
    [0, 8, 2, 2, 8, 11, 4, 9, 10, 4, 10, 6, -1, -1, -1, -1],
    [3, 11, 2, 0, 1, 6, 0, 6, 4, 6, 1, 10, -1, -1, -1, -1],
    [6, 4, 1, 6, 1, 10, 4, 8, 1, 2, 1, 11, 8, 11, 1, -1],
    [9, 6, 4, 9, 3, 6, 9, 1, 3, 11, 6, 3, -1, -1, -1, -1],
    [8, 11, 1, 8, 1, 0, 11, 6, 1, 9, 1, 4, 6, 4, 1, -1],
    [3, 11, 6, 3, 6, 0, 0, 6, 4, -1, -1, -1, -1, -1, -1, -1],
    [6, 4, 8, 11, 6, 8, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [7, 10, 6, 7, 8, 10, 8, 9, 10, -1, -1, -1, -1, -1, -1, -1],
    [0, 7, 3, 0, 10, 7, 0, 9, 10, 6, 7, 10, -1, -1, -1, -1],
    [10, 6, 7, 1, 10, 7, 1, 7, 8, 1, 8, 0, -1, -1, -1, -1],
    [10, 6, 7, 10, 7, 1, 1, 7, 3, -1, -1, -1, -1, -1, -1, -1],
    [1, 2, 6, 1, 6, 8, 1, 8, 9, 8, 6, 7, -1, -1, -1, -1],
    [2, 6, 9, 2, 9, 1, 6, 7, 9, 0, 9, 3, 7, 3, 9, -1],
    [7, 8, 0, 7, 0, 6, 6, 0, 2, -1, -1, -1, -1, -1, -1, -1],
    [7, 3, 2, 6, 7, 2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [2, 3, 11, 10, 6, 8, 10, 8, 9, 8, 6, 7, -1, -1, -1, -1],
    [2, 0, 7, 2, 7, 11, 0, 9, 7, 6, 7, 10, 9, 10, 7, -1],
    [1, 8, 0, 1, 7, 8, 1, 10, 7, 6, 7, 10, 2, 3, 11, -1],
    [11, 2, 1, 11, 1, 7, 10, 6, 1, 6, 7, 1, -1, -1, -1, -1],
    [8, 9, 6, 8, 6, 7, 9, 1, 6, 11, 6, 3, 1, 3, 6, -1],
    [0, 9, 1, 11, 6, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [7, 8, 0, 7, 0, 6, 3, 11, 0, 11, 6, 0, -1, -1, -1, -1],
    [7, 11, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [7, 6, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [3, 0, 8, 11, 7, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [0, 1, 9, 11, 7, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [8, 1, 9, 8, 3, 1, 11, 7, 6, -1, -1, -1, -1, -1, -1, -1],
    [10, 1, 2, 6, 11, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [1, 2, 10, 3, 0, 8, 6, 11, 7, -1, -1, -1, -1, -1, -1, -1],
    [2, 9, 0, 2, 10, 9, 6, 11, 7, -1, -1, -1, -1, -1, -1, -1],
    [6, 11, 7, 2, 10, 3, 10, 8, 3, 10, 9, 8, -1, -1, -1, -1],
    [7, 2, 3, 6, 2, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [7, 0, 8, 7, 6, 0, 6, 2, 0, -1, -1, -1, -1, -1, -1, -1],
    [2, 7, 6, 2, 3, 7, 0, 1, 9, -1, -1, -1, -1, -1, -1, -1],
    [1, 6, 2, 1, 8, 6, 1, 9, 8, 8, 7, 6, -1, -1, -1, -1],
    [10, 7, 6, 10, 1, 7, 1, 3, 7, -1, -1, -1, -1, -1, -1, -1],
    [10, 7, 6, 1, 7, 10, 1, 8, 7, 1, 0, 8, -1, -1, -1, -1],
    [0, 3, 7, 0, 7, 10, 0, 10, 9, 6, 10, 7, -1, -1, -1, -1],
    [7, 6, 10, 7, 10, 8, 8, 10, 9, -1, -1, -1, -1, -1, -1, -1],
    [6, 8, 4, 11, 8, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [3, 6, 11, 3, 0, 6, 0, 4, 6, -1, -1, -1, -1, -1, -1, -1],
    [8, 6, 11, 8, 4, 6, 9, 0, 1, -1, -1, -1, -1, -1, -1, -1],
    [9, 4, 6, 9, 6, 3, 9, 3, 1, 11, 3, 6, -1, -1, -1, -1],
    [6, 8, 4, 6, 11, 8, 2, 10, 1, -1, -1, -1, -1, -1, -1, -1],
    [1, 2, 10, 3, 0, 11, 0, 6, 11, 0, 4, 6, -1, -1, -1, -1],
    [4, 11, 8, 4, 6, 11, 0, 2, 9, 2, 10, 9, -1, -1, -1, -1],
    [10, 9, 3, 10, 3, 2, 9, 4, 3, 11, 3, 6, 4, 6, 3, -1],
    [8, 2, 3, 8, 4, 2, 4, 6, 2, -1, -1, -1, -1, -1, -1, -1],
    [0, 4, 2, 4, 6, 2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [1, 9, 0, 2, 3, 4, 2, 4, 6, 4, 3, 8, -1, -1, -1, -1],
    [1, 9, 4, 1, 4, 2, 2, 4, 6, -1, -1, -1, -1, -1, -1, -1],
    [8, 1, 3, 8, 6, 1, 8, 4, 6, 6, 10, 1, -1, -1, -1, -1],
    [10, 1, 0, 10, 0, 6, 6, 0, 4, -1, -1, -1, -1, -1, -1, -1],
    [4, 6, 3, 4, 3, 8, 6, 10, 3, 0, 3, 9, 10, 9, 3, -1],
    [10, 9, 4, 6, 10, 4, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [4, 9, 5, 7, 6, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [0, 8, 3, 4, 9, 5, 11, 7, 6, -1, -1, -1, -1, -1, -1, -1],
    [5, 0, 1, 5, 4, 0, 7, 6, 11, -1, -1, -1, -1, -1, -1, -1],
    [11, 7, 6, 8, 3, 4, 3, 5, 4, 3, 1, 5, -1, -1, -1, -1],
    [9, 5, 4, 10, 1, 2, 7, 6, 11, -1, -1, -1, -1, -1, -1, -1],
    [6, 11, 7, 1, 2, 10, 0, 8, 3, 4, 9, 5, -1, -1, -1, -1],
    [7, 6, 11, 5, 4, 10, 4, 2, 10, 4, 0, 2, -1, -1, -1, -1],
    [3, 4, 8, 3, 5, 4, 3, 2, 5, 10, 5, 2, 11, 7, 6, -1],
    [7, 2, 3, 7, 6, 2, 5, 4, 9, -1, -1, -1, -1, -1, -1, -1],
    [9, 5, 4, 0, 8, 6, 0, 6, 2, 6, 8, 7, -1, -1, -1, -1],
    [3, 6, 2, 3, 7, 6, 1, 5, 0, 5, 4, 0, -1, -1, -1, -1],
    [6, 2, 8, 6, 8, 7, 2, 1, 8, 4, 8, 5, 1, 5, 8, -1],
    [9, 5, 4, 10, 1, 6, 1, 7, 6, 1, 3, 7, -1, -1, -1, -1],
    [1, 6, 10, 1, 7, 6, 1, 0, 7, 8, 7, 0, 9, 5, 4, -1],
    [4, 0, 10, 4, 10, 5, 0, 3, 10, 6, 10, 7, 3, 7, 10, -1],
    [7, 6, 10, 7, 10, 8, 5, 4, 10, 4, 8, 10, -1, -1, -1, -1],
    [6, 9, 5, 6, 11, 9, 11, 8, 9, -1, -1, -1, -1, -1, -1, -1],
    [3, 6, 11, 0, 6, 3, 0, 5, 6, 0, 9, 5, -1, -1, -1, -1],
    [0, 11, 8, 0, 5, 11, 0, 1, 5, 5, 6, 11, -1, -1, -1, -1],
    [6, 11, 3, 6, 3, 5, 5, 3, 1, -1, -1, -1, -1, -1, -1, -1],
    [1, 2, 10, 9, 5, 11, 9, 11, 8, 11, 5, 6, -1, -1, -1, -1],
    [0, 11, 3, 0, 6, 11, 0, 9, 6, 5, 6, 9, 1, 2, 10, -1],
    [11, 8, 5, 11, 5, 6, 8, 0, 5, 10, 5, 2, 0, 2, 5, -1],
    [6, 11, 3, 6, 3, 5, 2, 10, 3, 10, 5, 3, -1, -1, -1, -1],
    [5, 8, 9, 5, 2, 8, 5, 6, 2, 3, 8, 2, -1, -1, -1, -1],
    [9, 5, 6, 9, 6, 0, 0, 6, 2, -1, -1, -1, -1, -1, -1, -1],
    [1, 5, 8, 1, 8, 0, 5, 6, 8, 3, 8, 2, 6, 2, 8, -1],
    [1, 5, 6, 2, 1, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [1, 3, 6, 1, 6, 10, 3, 8, 6, 5, 6, 9, 8, 9, 6, -1],
    [10, 1, 0, 10, 0, 6, 9, 5, 0, 5, 6, 0, -1, -1, -1, -1],
    [0, 3, 8, 5, 6, 10, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [10, 5, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [11, 5, 10, 7, 5, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [11, 5, 10, 11, 7, 5, 8, 3, 0, -1, -1, -1, -1, -1, -1, -1],
    [5, 11, 7, 5, 10, 11, 1, 9, 0, -1, -1, -1, -1, -1, -1, -1],
    [10, 7, 5, 10, 11, 7, 9, 8, 1, 8, 3, 1, -1, -1, -1, -1],
    [11, 1, 2, 11, 7, 1, 7, 5, 1, -1, -1, -1, -1, -1, -1, -1],
    [0, 8, 3, 1, 2, 7, 1, 7, 5, 7, 2, 11, -1, -1, -1, -1],
    [9, 7, 5, 9, 2, 7, 9, 0, 2, 2, 11, 7, -1, -1, -1, -1],
    [7, 5, 2, 7, 2, 11, 5, 9, 2, 3, 2, 8, 9, 8, 2, -1],
    [2, 5, 10, 2, 3, 5, 3, 7, 5, -1, -1, -1, -1, -1, -1, -1],
    [8, 2, 0, 8, 5, 2, 8, 7, 5, 10, 2, 5, -1, -1, -1, -1],
    [9, 0, 1, 5, 10, 3, 5, 3, 7, 3, 10, 2, -1, -1, -1, -1],
    [9, 8, 2, 9, 2, 1, 8, 7, 2, 10, 2, 5, 7, 5, 2, -1],
    [1, 3, 5, 3, 7, 5, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [0, 8, 7, 0, 7, 1, 1, 7, 5, -1, -1, -1, -1, -1, -1, -1],
    [9, 0, 3, 9, 3, 5, 5, 3, 7, -1, -1, -1, -1, -1, -1, -1],
    [9, 8, 7, 5, 9, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [5, 8, 4, 5, 10, 8, 10, 11, 8, -1, -1, -1, -1, -1, -1, -1],
    [5, 0, 4, 5, 11, 0, 5, 10, 11, 11, 3, 0, -1, -1, -1, -1],
    [0, 1, 9, 8, 4, 10, 8, 10, 11, 10, 4, 5, -1, -1, -1, -1],
    [10, 11, 4, 10, 4, 5, 11, 3, 4, 9, 4, 1, 3, 1, 4, -1],
    [2, 5, 1, 2, 8, 5, 2, 11, 8, 4, 5, 8, -1, -1, -1, -1],
    [0, 4, 11, 0, 11, 3, 4, 5, 11, 2, 11, 1, 5, 1, 11, -1],
    [0, 2, 5, 0, 5, 9, 2, 11, 5, 4, 5, 8, 11, 8, 5, -1],
    [9, 4, 5, 2, 11, 3, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [2, 5, 10, 3, 5, 2, 3, 4, 5, 3, 8, 4, -1, -1, -1, -1],
    [5, 10, 2, 5, 2, 4, 4, 2, 0, -1, -1, -1, -1, -1, -1, -1],
    [3, 10, 2, 3, 5, 10, 3, 8, 5, 4, 5, 8, 0, 1, 9, -1],
    [5, 10, 2, 5, 2, 4, 1, 9, 2, 9, 4, 2, -1, -1, -1, -1],
    [8, 4, 5, 8, 5, 3, 3, 5, 1, -1, -1, -1, -1, -1, -1, -1],
    [0, 4, 5, 1, 0, 5, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [8, 4, 5, 8, 5, 3, 9, 0, 5, 0, 3, 5, -1, -1, -1, -1],
    [9, 4, 5, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [4, 11, 7, 4, 9, 11, 9, 10, 11, -1, -1, -1, -1, -1, -1, -1],
    [0, 8, 3, 4, 9, 7, 9, 11, 7, 9, 10, 11, -1, -1, -1, -1],
    [1, 10, 11, 1, 11, 4, 1, 4, 0, 7, 4, 11, -1, -1, -1, -1],
    [3, 1, 4, 3, 4, 8, 1, 10, 4, 7, 4, 11, 10, 11, 4, -1],
    [4, 11, 7, 9, 11, 4, 9, 2, 11, 9, 1, 2, -1, -1, -1, -1],
    [9, 7, 4, 9, 11, 7, 9, 1, 11, 2, 11, 1, 0, 8, 3, -1],
    [11, 7, 4, 11, 4, 2, 2, 4, 0, -1, -1, -1, -1, -1, -1, -1],
    [11, 7, 4, 11, 4, 2, 8, 3, 4, 3, 2, 4, -1, -1, -1, -1],
    [2, 9, 10, 2, 7, 9, 2, 3, 7, 7, 4, 9, -1, -1, -1, -1],
    [9, 10, 7, 9, 7, 4, 10, 2, 7, 8, 7, 0, 2, 0, 7, -1],
    [3, 7, 10, 3, 10, 2, 7, 4, 10, 1, 10, 0, 4, 0, 10, -1],
    [1, 10, 2, 8, 7, 4, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [4, 9, 1, 4, 1, 7, 7, 1, 3, -1, -1, -1, -1, -1, -1, -1],
    [4, 9, 1, 4, 1, 7, 0, 8, 1, 8, 7, 1, -1, -1, -1, -1],
    [4, 0, 3, 7, 4, 3, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [4, 8, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [9, 10, 8, 10, 11, 8, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [3, 0, 9, 3, 9, 11, 11, 9, 10, -1, -1, -1, -1, -1, -1, -1],
    [0, 1, 10, 0, 10, 8, 8, 10, 11, -1, -1, -1, -1, -1, -1, -1],
    [3, 1, 10, 11, 3, 10, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [1, 2, 11, 1, 11, 9, 9, 11, 8, -1, -1, -1, -1, -1, -1, -1],
    [3, 0, 9, 3, 9, 11, 1, 2, 9, 2, 11, 9, -1, -1, -1, -1],
    [0, 2, 11, 8, 0, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [3, 2, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [2, 3, 8, 2, 8, 10, 10, 8, 9, -1, -1, -1, -1, -1, -1, -1],
    [9, 10, 2, 0, 9, 2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [2, 3, 8, 2, 8, 10, 0, 1, 8, 1, 10, 8, -1, -1, -1, -1],
    [1, 10, 2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [1, 3, 8, 9, 1, 8, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [0, 9, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [0, 3, 8, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
    [
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    ],
];

// ── Corner / edge helper data ─────────────────────────────────────────────────

/// Offsets of the 8 cube corners relative to (ix, iy, iz).
const CORNER_OFFSETS: [[usize; 3]; 8] = [
    [0, 0, 0], // 0
    [1, 0, 0], // 1
    [1, 1, 0], // 2
    [0, 1, 0], // 3
    [0, 0, 1], // 4
    [1, 0, 1], // 5
    [1, 1, 1], // 6
    [0, 1, 1], // 7
];

/// For each of the 12 edges: [corner_a, corner_b].
const EDGE_CORNERS: [[usize; 2]; 12] = [
    [0, 1], // 0
    [1, 2], // 1
    [2, 3], // 2
    [3, 0], // 3
    [4, 5], // 4
    [5, 6], // 5
    [6, 7], // 6
    [7, 4], // 7
    [0, 4], // 8
    [1, 5], // 9
    [2, 6], // 10
    [3, 7], // 11
];

// ── ScalarField ───────────────────────────────────────────────────────────────

/// A 3D scalar field for isosurface extraction.
pub struct ScalarField {
    pub data: Vec<f32>,
    pub dims: [usize; 3],  // [nx, ny, nz]
    pub origin: [f32; 3],  // world-space origin
    pub spacing: [f32; 3], // voxel size in each dimension
}

impl ScalarField {
    /// Create a new scalar field, initialised to zero.
    pub fn new(dims: [usize; 3], origin: [f32; 3], spacing: [f32; 3]) -> Self {
        let total = dims[0] * dims[1] * dims[2];
        ScalarField {
            data: vec![0.0f32; total],
            dims,
            origin,
            spacing,
        }
    }

    #[inline]
    fn index(&self, ix: usize, iy: usize, iz: usize) -> usize {
        ix + self.dims[0] * (iy + self.dims[1] * iz)
    }

    /// Get value at grid index (ix, iy, iz).
    pub fn get(&self, ix: usize, iy: usize, iz: usize) -> f32 {
        self.data[self.index(ix, iy, iz)]
    }

    /// Set value at grid index.
    pub fn set(&mut self, ix: usize, iy: usize, iz: usize, value: f32) {
        let idx = self.index(ix, iy, iz);
        self.data[idx] = value;
    }

    /// World position of grid point (ix, iy, iz).
    pub fn world_pos(&self, ix: usize, iy: usize, iz: usize) -> [f32; 3] {
        [
            self.origin[0] + ix as f32 * self.spacing[0],
            self.origin[1] + iy as f32 * self.spacing[1],
            self.origin[2] + iz as f32 * self.spacing[2],
        ]
    }

    /// Fill the field with a sphere SDF: value = radius - distance_from_center.
    /// Positive inside the sphere, negative outside.
    pub fn fill_sphere_sdf(&mut self, center: [f32; 3], radius: f32) {
        let [nx, ny, nz] = self.dims;
        for iz in 0..nz {
            for iy in 0..ny {
                for ix in 0..nx {
                    let p = self.world_pos(ix, iy, iz);
                    let dx = p[0] - center[0];
                    let dy = p[1] - center[1];
                    let dz = p[2] - center[2];
                    let dist = (dx * dx + dy * dy + dz * dz).sqrt();
                    let idx = self.index(ix, iy, iz);
                    self.data[idx] = radius - dist;
                }
            }
        }
    }

    /// Fill with a torus SDF centred at `center`.
    /// `major_radius` R = distance from tube centre to torus centre.
    /// `minor_radius` r = tube radius.
    /// Value = r - (sqrt(x^2+z^2) - R)^2 + y^2)^(1/2) (positive inside).
    pub fn fill_torus_sdf(&mut self, center: [f32; 3], major_radius: f32, minor_radius: f32) {
        let [nx, ny, nz] = self.dims;
        for iz in 0..nz {
            for iy in 0..ny {
                for ix in 0..nx {
                    let p = self.world_pos(ix, iy, iz);
                    let dx = p[0] - center[0];
                    let dy = p[1] - center[1];
                    let dz = p[2] - center[2];
                    // Torus in XZ plane
                    let r_xz = (dx * dx + dz * dz).sqrt();
                    let q = r_xz - major_radius;
                    let dist = (q * q + dy * dy).sqrt();
                    let idx = self.index(ix, iy, iz);
                    self.data[idx] = minor_radius - dist;
                }
            }
        }
    }

    /// Fill with a box SDF.  Value = min component of (half_extents - |p - center|).
    /// Positive inside, negative outside.
    pub fn fill_box_sdf(&mut self, center: [f32; 3], half_extents: [f32; 3]) {
        let [nx, ny, nz] = self.dims;
        for iz in 0..nz {
            for iy in 0..ny {
                for ix in 0..nx {
                    let p = self.world_pos(ix, iy, iz);
                    let dx = (p[0] - center[0]).abs();
                    let dy = (p[1] - center[1]).abs();
                    let dz = (p[2] - center[2]).abs();
                    // Inside: all distances < half_extents  → positive value
                    // Outside: exact Euclidean SDF
                    let qx = dx - half_extents[0];
                    let qy = dy - half_extents[1];
                    let qz = dz - half_extents[2];
                    let outside = (qx.max(0.0) * qx.max(0.0)
                        + qy.max(0.0) * qy.max(0.0)
                        + qz.max(0.0) * qz.max(0.0))
                    .sqrt();
                    let inside = qx.max(qy).max(qz).min(0.0);
                    let idx = self.index(ix, iy, iz);
                    // SDF positive inside, negative outside  → negate standard SDF sign
                    self.data[idx] = -(outside + inside);
                }
            }
        }
    }
}

// ── Marching Cubes core ───────────────────────────────────────────────────────

/// Linearly interpolate between two edge endpoints to find the isosurface crossing.
#[inline]
fn interp_vertex(p0: [f32; 3], p1: [f32; 3], v0: f32, v1: f32, isovalue: f32) -> [f32; 3] {
    let denom = v1 - v0;
    let t = if denom.abs() < 1e-10 {
        0.5
    } else {
        ((isovalue - v0) / denom).clamp(0.0, 1.0)
    };
    [
        p0[0] + t * (p1[0] - p0[0]),
        p0[1] + t * (p1[1] - p0[1]),
        p0[2] + t * (p1[2] - p0[2]),
    ]
}

/// Extract an isosurface at the given isovalue using the Marching Cubes algorithm.
/// Returns a MeshBuffers (positions, normals computed from triangles, dummy UVs, indices).
pub fn marching_cubes(field: &ScalarField, isovalue: f32) -> MeshBuffers {
    let [nx, ny, nz] = field.dims;
    if nx < 2 || ny < 2 || nz < 2 {
        return empty_mesh();
    }

    let mut positions: Vec<[f32; 3]> = Vec::new();
    let mut indices: Vec<u32> = Vec::new();

    for iz in 0..nz - 1 {
        for iy in 0..ny - 1 {
            for ix in 0..nx - 1 {
                process_cube(field, ix, iy, iz, isovalue, &mut positions, &mut indices);
            }
        }
    }

    build_mesh(positions, indices)
}

/// Marching cubes with vertex welding (merge vertices closer than epsilon).
pub fn marching_cubes_welded(field: &ScalarField, isovalue: f32, epsilon: f32) -> MeshBuffers {
    let raw = marching_cubes(field, isovalue);
    if raw.positions.is_empty() {
        return raw;
    }
    weld_mesh(raw, epsilon)
}

// ── Internal helpers ──────────────────────────────────────────────────────────

fn empty_mesh() -> MeshBuffers {
    MeshBuffers {
        positions: Vec::new(),
        normals: Vec::new(),
        tangents: Vec::new(),
        uvs: Vec::new(),
        indices: Vec::new(),
        colors: None,
        has_suit: false,
    }
}

fn process_cube(
    field: &ScalarField,
    ix: usize,
    iy: usize,
    iz: usize,
    isovalue: f32,
    positions: &mut Vec<[f32; 3]>,
    indices: &mut Vec<u32>,
) {
    // Gather corner values and positions
    let mut corner_vals = [0.0f32; 8];
    let mut corner_pos = [[0.0f32; 3]; 8];

    for (c, off) in CORNER_OFFSETS.iter().enumerate() {
        let cx = ix + off[0];
        let cy = iy + off[1];
        let cz = iz + off[2];
        corner_vals[c] = field.get(cx, cy, cz);
        corner_pos[c] = field.world_pos(cx, cy, cz);
    }

    // Compute 8-bit case index
    let mut case_idx: usize = 0;
    for (c, &val) in corner_vals.iter().enumerate() {
        if val > isovalue {
            case_idx |= 1 << c;
        }
    }

    // Skip fully inside or fully outside
    if case_idx == 0 || case_idx == 255 {
        return;
    }

    let edge_mask = EDGE_TABLE[case_idx];
    if edge_mask == 0 {
        return;
    }

    // Compute edge vertex positions for all active edges
    let mut edge_verts = [[0.0f32; 3]; 12];
    for e in 0..12u16 {
        if edge_mask & (1 << e) != 0 {
            let [ca, cb] = EDGE_CORNERS[e as usize];
            edge_verts[e as usize] = interp_vertex(
                corner_pos[ca],
                corner_pos[cb],
                corner_vals[ca],
                corner_vals[cb],
                isovalue,
            );
        }
    }

    // Emit triangles
    let tri_row = &TRI_TABLE[case_idx];
    let mut k = 0;
    while k < 15 {
        let e0 = tri_row[k];
        if e0 < 0 {
            break;
        }
        let e1 = tri_row[k + 1];
        let e2 = tri_row[k + 2];
        let base = positions.len() as u32;
        positions.push(edge_verts[e0 as usize]);
        positions.push(edge_verts[e1 as usize]);
        positions.push(edge_verts[e2 as usize]);
        indices.push(base);
        indices.push(base + 1);
        indices.push(base + 2);
        k += 3;
    }
}

fn build_mesh(positions: Vec<[f32; 3]>, indices: Vec<u32>) -> MeshBuffers {
    let n = positions.len();
    let uvs = vec![[0.0f32; 2]; n];
    let tangents = vec![[1.0f32, 0.0, 0.0, 1.0]; n];
    let normals = vec![[0.0f32, 1.0, 0.0]; n];

    let mut mesh = MeshBuffers {
        positions,
        normals,
        tangents,
        uvs,
        indices,
        colors: None,
        has_suit: false,
    };
    compute_normals(&mut mesh);
    mesh
}

/// Simple spatial welding: merge vertices closer than epsilon.
/// Uses an O(n^2) approach which is fine for moderate mesh sizes.
fn weld_mesh(src: MeshBuffers, epsilon: f32) -> MeshBuffers {
    let eps2 = epsilon * epsilon;
    let n = src.positions.len();

    let mut new_positions: Vec<[f32; 3]> = Vec::with_capacity(n);
    // Map from old index → new index
    let mut remap: Vec<u32> = vec![u32::MAX; n];

    for (remap_slot, &p) in remap.iter_mut().zip(src.positions.iter()) {
        // Find an existing vertex within epsilon
        let mut found = u32::MAX;
        for (j, &q) in new_positions.iter().enumerate() {
            let dx = p[0] - q[0];
            let dy = p[1] - q[1];
            let dz = p[2] - q[2];
            if dx * dx + dy * dy + dz * dz <= eps2 {
                found = j as u32;
                break;
            }
        }
        if found == u32::MAX {
            *remap_slot = new_positions.len() as u32;
            new_positions.push(p);
        } else {
            *remap_slot = found;
        }
    }

    // Remap indices; skip degenerate triangles
    let mut new_indices: Vec<u32> = Vec::with_capacity(src.indices.len());
    for tri in src.indices.chunks_exact(3) {
        let i0 = remap[tri[0] as usize];
        let i1 = remap[tri[1] as usize];
        let i2 = remap[tri[2] as usize];
        if i0 != i1 && i1 != i2 && i2 != i0 {
            new_indices.push(i0);
            new_indices.push(i1);
            new_indices.push(i2);
        }
    }

    build_mesh(new_positions, new_indices)
}

// ── Tests ─────────────────────────────────────────────────────────────────────

#[cfg(test)]
mod tests {
    use super::*;

    const N: usize = 16;

    fn unit_field() -> ScalarField {
        ScalarField::new([N, N, N], [-1.0, -1.0, -1.0], [2.0 / (N - 1) as f32; 3])
    }

    // ── ScalarField basic tests ───────────────────────────────────────────

    #[test]
    fn scalar_field_set_get() {
        let mut f = unit_field();
        f.set(3, 5, 7, 42.0);
        assert!((f.get(3, 5, 7) - 42.0).abs() < 1e-6);
    }

    #[test]
    fn scalar_field_world_pos() {
        let f = ScalarField::new([3, 3, 3], [0.0, 0.0, 0.0], [1.0, 1.0, 1.0]);
        let p = f.world_pos(2, 1, 0);
        assert!((p[0] - 2.0).abs() < 1e-6);
        assert!((p[1] - 1.0).abs() < 1e-6);
        assert!((p[2] - 0.0).abs() < 1e-6);
    }

    // ── Sphere SDF tests ──────────────────────────────────────────────────

    #[test]
    fn fill_sphere_sdf_positive_inside() {
        let mut f = unit_field();
        f.fill_sphere_sdf([0.0, 0.0, 0.0], 0.5);
        // Centre voxel should be positive (inside sphere)
        let mid = N / 2;
        assert!(f.get(mid, mid, mid) > 0.0, "centre should be inside sphere");
    }

    #[test]
    fn fill_sphere_sdf_negative_outside() {
        let mut f = unit_field();
        f.fill_sphere_sdf([0.0, 0.0, 0.0], 0.5);
        // Corner should be negative (outside sphere)
        assert!(f.get(0, 0, 0) < 0.0, "corner should be outside sphere");
    }

    // ── Marching cubes sphere tests ───────────────────────────────────────

    #[test]
    fn marching_cubes_sphere_has_faces() {
        let mut f = unit_field();
        f.fill_sphere_sdf([0.0, 0.0, 0.0], 0.5);
        let m = marching_cubes(&f, 0.0);
        assert!(m.face_count() > 0, "sphere should produce faces");
    }

    #[test]
    fn marching_cubes_sphere_positions_finite() {
        let mut f = unit_field();
        f.fill_sphere_sdf([0.0, 0.0, 0.0], 0.5);
        let m = marching_cubes(&f, 0.0);
        for p in &m.positions {
            assert!(
                p[0].is_finite() && p[1].is_finite() && p[2].is_finite(),
                "non-finite position: {:?}",
                p
            );
        }
    }

    #[test]
    fn marching_cubes_sphere_normals_valid() {
        let mut f = unit_field();
        f.fill_sphere_sdf([0.0, 0.0, 0.0], 0.5);
        let m = marching_cubes(&f, 0.0);
        assert_eq!(m.normals.len(), m.positions.len());
        for n in &m.normals {
            let len = (n[0] * n[0] + n[1] * n[1] + n[2] * n[2]).sqrt();
            assert!(len > 0.5, "degenerate normal: {:?}", n);
            assert!(n[0].is_finite() && n[1].is_finite() && n[2].is_finite());
        }
    }

    // ── Empty field test ──────────────────────────────────────────────────

    #[test]
    fn marching_cubes_empty_field_no_faces() {
        let f = unit_field(); // all zeros; isovalue = 1.0 → no crossings
        let m = marching_cubes(&f, 1.0);
        assert_eq!(m.face_count(), 0, "uniform field should produce no faces");
    }

    // ── Welded mesh test ──────────────────────────────────────────────────

    #[test]
    fn marching_cubes_welded_fewer_vertices() {
        let mut f = unit_field();
        f.fill_sphere_sdf([0.0, 0.0, 0.0], 0.5);
        let raw = marching_cubes(&f, 0.0);
        let welded = marching_cubes_welded(&f, 0.0, 1e-4);
        assert!(
            welded.vertex_count() <= raw.vertex_count(),
            "welded should not have more vertices than raw"
        );
    }

    // ── Box SDF test ──────────────────────────────────────────────────────

    #[test]
    fn marching_cubes_box_sdf_has_faces() {
        let mut f = unit_field();
        f.fill_box_sdf([0.0, 0.0, 0.0], [0.4, 0.4, 0.4]);
        let m = marching_cubes(&f, 0.0);
        assert!(m.face_count() > 0, "box SDF should produce faces");
    }

    // ── Torus test ────────────────────────────────────────────────────────

    #[test]
    fn scalar_field_fill_torus() {
        let mut f = unit_field();
        f.fill_torus_sdf([0.0, 0.0, 0.0], 0.4, 0.15);
        let m = marching_cubes(&f, 0.0);
        // Torus should produce faces at this scale
        assert!(m.face_count() > 0, "torus SDF should produce faces");
    }
}