Restore preflight.py from Make-It-Animatable

preflight.py

@@ -0,0 +1,78 @@
+"""Bounded GLB metadata preflight; does not load textures or allocate mesh arrays."""
+import json
+import struct
+from pathlib import Path
+
+MAX_FACES = 500_000
+MAX_VERTICES = 500_000
+MAX_JSON = 16 * 1024 * 1024
+
+def inspect_glb(path):
+    path = Path(path)
+    size = path.stat().st_size
+    with path.open("rb") as stream:
+        header = stream.read(20)
+        if len(header) != 20:
+            raise ValueError("Truncated GLB header")
+        magic, version, length, json_length, chunk = struct.unpack("<4sIIII", header)
+        if magic != b"glTF" or version != 2 or length != size or chunk != 0x4E4F534A:
+            raise ValueError("Invalid GLB 2.0 header or file length")
+        if json_length > MAX_JSON or json_length > size - 20:
+            raise ValueError("GLB metadata is too large or truncated")
+        doc = json.loads(stream.read(json_length))
+    meshes = doc.get("meshes", [])
+    accessors = doc.get("accessors", [])
+    vertices = faces = 0
+    unsupported = False
+    for mesh in meshes:
+        for primitive in mesh.get("primitives", []):
+            if primitive.get("mode", 4) != 4:
+                unsupported = True
+                continue
+            position = primitive.get("attributes", {}).get("POSITION")
+            if position is None:
+                raise ValueError("Mesh primitive has no POSITION accessor")
+            count = int(accessors[position]["count"])
+            index = primitive.get("indices")
+            indices = int(accessors[index]["count"]) if index is not None else count
+            if count < 0 or indices < 0 or indices % 3:
+                raise ValueError("Invalid vertex or triangle count")
+            vertices += count
+            faces += indices // 3
+    # Count node instances because upstream merges transformed scene geometry.
+    nodes = doc.get("nodes", [])
+    instances = {}
+    for node in nodes:
+        if "mesh" in node:
+            instances[node["mesh"]] = instances.get(node["mesh"], 0) + 1
+    instantiated_faces = 0
+    instantiated_vertices = 0
+    for i, mesh in enumerate(meshes):
+        multiplicity = max(1, instances.get(i, 0))
+        for primitive in mesh.get("primitives", []):
+            pos = primitive.get("attributes", {}).get("POSITION")
+            if pos is None:
+                continue
+            count = int(accessors[pos]["count"])
+            index = primitive.get("indices")
+            n = int(accessors[index]["count"]) if index is not None else count
+            instantiated_vertices += count * multiplicity
+            if primitive.get("mode", 4) == 4:
+                instantiated_faces += n // 3 * multiplicity
+    required_extensions = doc.get("extensionsRequired", [])
+    unsupported = unsupported or any(x in required_extensions for x in
+                                     ("KHR_draco_mesh_compression", "EXT_meshopt_compression"))
+    dense = instantiated_faces > MAX_FACES or instantiated_vertices > MAX_VERTICES or size > 512 * 1024**2
+    warning = ("Preprocessing/decimation required: this input exceeds the conservative "
+               "500,000-face or 500,000-vertex limit. The original is preserved; "
+               "inference has not started.") if dense else ""
+    if unsupported:
+        warning = "Preprocessing required: export uncompressed triangle geometry before inference."
+    return dict(file_size_bytes=size, mesh_count=len(meshes), vertices=vertices,
+                triangles=faces, instantiated_vertices=instantiated_vertices,
+                instantiated_triangles=instantiated_faces,
+                materials=len(doc.get("materials", [])),
+                textures_present=bool(doc.get("textures") or doc.get("images")),
+                density_risk="high" if dense else "within conservative limit",
+                inference_allowed=bool(meshes) and faces > 0 and not dense and not unsupported,
+                warning=warning)