examples/read_one_sample.py

"""Read one object from a TexSet shard and put a UV layout onto its mesh.

    pip install numpy trimesh pillow
    python examples/read_one_sample.py data/val/val-00000-of-00001.tar [uid]

Members of one object are adjacent in the tar and share the uid as key:
    <uid>.glb  <uid>.uv.npz  <uid>.tex_A.png  <uid>.tex_B.png  <uid>.tex_C.png  <uid>.meta.json
"""
import hashlib, io, json, sys, tarfile

import numpy as np


def read_sample(tar_path, want_uid=None):
    with tarfile.open(tar_path, "r:") as tf:
        key, out = None, {}
        for m in tf:
            if not m.isfile():
                continue
            uid, ext = m.name.split(".", 1)
            if want_uid is not None and uid != want_uid:
                if key is not None:
                    break
                continue
            if key is None:
                key = uid
            if uid != key:
                break
            out[ext] = tf.extractfile(m).read()
    if key is None:
        raise KeyError(want_uid)
    return key, out


def load_mesh_like_texset(glb_bytes):
    """Exactly the vertex welding the UV sets were built against (loader
    `TextureTools.load_whole_mesh+Texture.from_trimesh`, reproduced with plain trimesh 5.1):
    load with process=False, bake the scene graph, concatenate, then three merge_vertices passes."""
    import trimesh
    from trimesh.visual.texture import TextureVisuals
    s = trimesh.load(io.BytesIO(glb_bytes), file_type="glb", process=False)
    if isinstance(s, trimesh.Scene):
        g = s.dump()
        m = g[0] if len(g) == 1 else trimesh.util.concatenate(g)
    else:
        m = s
    m.merge_vertices(merge_tex=False, merge_norm=True)
    m = m.copy(include_cache=True)
    if isinstance(m.visual, TextureVisuals):
        m.visual.vertex_attributes.update(m.visual.vertex_attributes.data)
    m.merge_vertices(merge_tex=False, merge_norm=True)
    m = m.copy(include_cache=True)
    m.merge_vertices(merge_tex=True, merge_norm=True)
    return np.asarray(m.vertices, np.float32), np.asarray(m.faces, np.int32)


def fingerprint(V, F):
    h = hashlib.sha256()
    h.update(np.ascontiguousarray(V, np.float32).tobytes())
    h.update(np.ascontiguousarray(F, np.int32).tobytes())
    return h.hexdigest()


if __name__ == "__main__":
    uid, raw = read_sample(sys.argv[1], sys.argv[2] if len(sys.argv) > 2 else None)
    meta = json.loads(raw["meta.json"])
    uv = np.load(io.BytesIO(raw["uv.npz"]))
    print(f"uid {uid}: {meta['n_faces']:,} faces, {meta['n_vertices']:,} vertices, loader {meta['loader']}")
    for name in ("A", "B", "C"):
        uv_vertices = uv[f"{name}/uv_vertices"].astype(np.float32) / 65535.0     # (K,2) in [0,1]
        uv_faces = uv[f"{name}/uv_faces"]                                          # (F,3), row i <-> mesh face i
        v = meta["variants"][name]
        print(f"  variant {name}: {len(uv_vertices):,} uv vertices, {v['charts']} charts, "
              f"utilization {v['utilization']:.3f}, faces without texel {v['faces_without_texel']}")

    # the atlas: RGBA, alpha = chart-coverage mask (NOT transparency); row 0 is v = 0 (no flip)
    try:
        from PIL import Image
        tex = np.asarray(Image.open(io.BytesIO(raw["tex_A.png"])))
        print(f"  tex_A {tex.shape} {tex.dtype}, covered texels {(tex[..., 3] > 0).mean():.1%}")
    except ImportError:
        print("  (install pillow to decode the atlases)")

    # bind UV set A to the mesh and check the fingerprint
    try:
        V, F = load_mesh_like_texset(raw["glb"])
        if meta["fingerprint"] is None:                      # a pruned object: sealed faces were deleted after baking
            ok = len(F) == meta["n_faces"]
            print(f"  mesh from glb: {len(F):,} faces; pruned object ({meta['pruned']['faces_removed']} faces removed), "
                  f"no fingerprint - face count {'OK' if ok else 'MISMATCH'}")
        else:
            ok = fingerprint(V, F) == meta["fingerprint"]
            print(f"  mesh from glb: {len(F):,} faces; fingerprint {'OK' if ok else 'MISMATCH'}")
        if ok:
            uv_a = uv["A/uv_vertices"].astype(np.float32) / 65535.0
            corner_uv = uv_a[uv["A/uv_faces"]]                                  # (F,3,2) per-corner UV
            H, W = tex.shape[:2]
            centre = corner_uv.mean(1)
            col = np.clip((centre[:, 0] * W).astype(int), 0, W - 1)
            row = np.clip((centre[:, 1] * H).astype(int), 0, H - 1)            # row = v*H, no flip
            print(f"  albedo at face centres, first 3 faces: {tex[row[:3], col[:3], :3].tolist()}")
    except ImportError:
        print("  (install trimesh to load the mesh and verify the fingerprint)")