vr-app/tools/make_calibration_glb.py

"""Génère calibration.glb — le repère de calibration de l'étape E1.

Trois branches de longueurs DIFFÉRENTES, aux couleurs de la convention habituelle :
    +X rouge  (1.00 m)   +Y vert (0.60 m)   +Z bleu (0.30 m)

Pourquoi trois longueurs différentes : un repère symétrique ne permet pas de voir
une inversion d'axe. Ici, si la conversion glTF -> Unity se trompe de signe, la
branche rouge part du mauvais côté par rapport à la bleue, et ça se voit sans
mesurer.

Le modèle est écrit en coordonnées glTF (main droite, Y-up, mètres) — c'est-à-dire
exactement la convention du manifeste. C'est ce qui en fait un test valable :
l'app place un marqueur AUX MÊMES coordonnées, sans passer par l'importeur.

Usage :  python3 make_calibration_glb.py [chemin/de/sortie.glb]
"""

import base64
import json
import struct
import sys
from pathlib import Path

AXES = [
    # (nom, dimensions du pavé, couleur RGBA)
    ("AxisX", (1.00, 0.04, 0.04), (0.85, 0.15, 0.15, 1.0)),
    ("AxisY", (0.04, 0.60, 0.04), (0.15, 0.75, 0.20, 1.0)),
    ("AxisZ", (0.04, 0.04, 0.30), (0.15, 0.35, 0.90, 1.0)),
]

FACES = [
    ((0, 0, 1), [(0, 0, 1), (1, 0, 1), (1, 1, 1), (0, 1, 1)]),
    ((0, 0, -1), [(1, 0, 0), (0, 0, 0), (0, 1, 0), (1, 1, 0)]),
    ((1, 0, 0), [(1, 0, 1), (1, 0, 0), (1, 1, 0), (1, 1, 1)]),
    ((-1, 0, 0), [(0, 0, 0), (0, 0, 1), (0, 1, 1), (0, 1, 0)]),
    ((0, 1, 0), [(0, 1, 1), (1, 1, 1), (1, 1, 0), (0, 1, 0)]),
    ((0, -1, 0), [(0, 0, 0), (1, 0, 0), (1, 0, 1), (0, 0, 1)]),
]


def box(size):
    """Pavé dont un coin est à l'origine et qui s'étend vers +X, +Y, +Z."""
    positions, normals, indices = [], [], []
    for normal, corners in FACES:
        base = len(positions)
        for cx, cy, cz in corners:
            positions.append((cx * size[0], cy * size[1], cz * size[2]))
            normals.append(normal)
        indices += [base, base + 1, base + 2, base, base + 2, base + 3]
    return positions, normals, indices


def main(out_path):
    buffer = bytearray()
    buffer_views, accessors, meshes, materials, nodes = [], [], [], [], []

    def add_view(data, target):
        while len(buffer) % 4:
            buffer.append(0)
        offset = len(buffer)
        buffer.extend(data)
        buffer_views.append(
            {"buffer": 0, "byteOffset": offset, "byteLength": len(data), "target": target}
        )
        return len(buffer_views) - 1

    for name, size, color in AXES:
        positions, normals, indices = box(size)

        pos_view = add_view(b"".join(struct.pack("<3f", *p) for p in positions), 34962)
        nrm_view = add_view(b"".join(struct.pack("<3f", *n) for n in normals), 34962)
        idx_view = add_view(b"".join(struct.pack("<H", i) for i in indices), 34963)

        accessors.append({
            "bufferView": pos_view, "componentType": 5126, "count": len(positions),
            "type": "VEC3",
            "min": [min(p[i] for p in positions) for i in range(3)],
            "max": [max(p[i] for p in positions) for i in range(3)],
        })
        accessors.append({
            "bufferView": nrm_view, "componentType": 5126, "count": len(normals),
            "type": "VEC3",
        })
        accessors.append({
            "bufferView": idx_view, "componentType": 5123, "count": len(indices),
            "type": "SCALAR",
        })

        base = len(accessors) - 3
        materials.append({
            "name": name + "Mat",
            "pbrMetallicRoughness": {
                "baseColorFactor": list(color), "metallicFactor": 0.0, "roughnessFactor": 0.8,
            },
        })
        meshes.append({
            "name": name,
            "primitives": [{
                "attributes": {"POSITION": base, "NORMAL": base + 1},
                "indices": base + 2,
                "material": len(materials) - 1,
            }],
        })
        nodes.append({"name": name, "mesh": len(meshes) - 1})

    gltf = {
        "asset": {
            "version": "2.0",
            "generator": "MyInfoMate VR — make_calibration_glb.py",
        },
        "scene": 0,
        "scenes": [{"name": "Calibration", "nodes": list(range(len(nodes)))}],
        "nodes": nodes,
        "meshes": meshes,
        "materials": materials,
        "accessors": accessors,
        "bufferViews": buffer_views,
        "buffers": [{"byteLength": len(buffer)}],
    }

    json_chunk = json.dumps(gltf, separators=(",", ":")).encode("utf-8")
    json_chunk += b" " * (-len(json_chunk) % 4)
    bin_chunk = bytes(buffer) + b"\0" * (-len(buffer) % 4)

    glb = struct.pack("<III", 0x46546C67, 2, 12 + 8 + len(json_chunk) + 8 + len(bin_chunk))
    glb += struct.pack("<II", len(json_chunk), 0x4E4F534A) + json_chunk
    glb += struct.pack("<II", len(bin_chunk), 0x004E4942) + bin_chunk

    Path(out_path).parent.mkdir(parents=True, exist_ok=True)
    Path(out_path).write_bytes(glb)
    print(f"{out_path} — {len(glb)} octets, {len(nodes)} branches")


if __name__ == "__main__":
    main(sys.argv[1] if len(sys.argv) > 1 else "calibration.glb")