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	import os
	import cv2
	import torch
	import trimesh
	import numpy as np

	from kiui.op import safe_normalize, dot
	from kiui.typing import *

	class Mesh:
	"""
	A torch-native trimesh class, with support for ``ply/obj/glb`` formats.

	Note:
	This class only supports one mesh with a single texture image (an albedo texture and a metallic-roughness texture).
	"""
	def __init__(
	self,
	v: Optional[Tensor] = None,
	f: Optional[Tensor] = None,
	vn: Optional[Tensor] = None,
	fn: Optional[Tensor] = None,
	vt: Optional[Tensor] = None,
	ft: Optional[Tensor] = None,
	vc: Optional[Tensor] = None, # vertex color
	albedo: Optional[Tensor] = None,
	metallicRoughness: Optional[Tensor] = None,
	device: Optional[torch.device] = None,
	):
	"""Init a mesh directly using all attributes.

	Args:
	v (Optional[Tensor]): vertices, float [N, 3]. Defaults to None.
	f (Optional[Tensor]): faces, int [M, 3]. Defaults to None.
	vn (Optional[Tensor]): vertex normals, float [N, 3]. Defaults to None.
	fn (Optional[Tensor]): faces for normals, int [M, 3]. Defaults to None.
	vt (Optional[Tensor]): vertex uv coordinates, float [N, 2]. Defaults to None.
	ft (Optional[Tensor]): faces for uvs, int [M, 3]. Defaults to None.
	vc (Optional[Tensor]): vertex colors, float [N, 3]. Defaults to None.
	albedo (Optional[Tensor]): albedo texture, float [H, W, 3], RGB format. Defaults to None.
	metallicRoughness (Optional[Tensor]): metallic-roughness texture, float [H, W, 3], metallic(Blue) = metallicRoughness[..., 2], roughness(Green) = metallicRoughness[..., 1]. Defaults to None.
	device (Optional[torch.device]): torch device. Defaults to None.
	"""
	self.device = device
	self.v = v
	self.vn = vn
	self.vt = vt
	self.f = f
	self.fn = fn
	self.ft = ft
	# will first see if there is vertex color to use
	self.vc = vc
	# only support a single albedo image
	self.albedo = albedo
	# pbr extension, metallic(Blue) = metallicRoughness[..., 2], roughness(Green) = metallicRoughness[..., 1]
	# ref: https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html
	self.metallicRoughness = metallicRoughness

	self.ori_center = 0
	self.ori_scale = 1

	@classmethod
	def load(cls, path, resize=True, clean=False, renormal=True, retex=False, bound=0.9, front_dir='+z', **kwargs):
	"""load mesh from path.

	Args:
	path (str): path to mesh file, supports ply, obj, glb.
	clean (bool, optional): perform mesh cleaning at load (e.g., merge close vertices). Defaults to False.
	resize (bool, optional): auto resize the mesh using ``bound`` into [-bound, bound]^3. Defaults to True.
	renormal (bool, optional): re-calc the vertex normals. Defaults to True.
	retex (bool, optional): re-calc the uv coordinates, will overwrite the existing uv coordinates. Defaults to False.
	bound (float, optional): bound to resize. Defaults to 0.9.
	front_dir (str, optional): front-view direction of the mesh, should be [+-][xyz][ 123]. Defaults to '+z'.
	device (torch.device, optional): torch device. Defaults to None.

	Note:
	a ``device`` keyword argument can be provided to specify the torch device.
	If it's not provided, we will try to use ``'cuda'`` as the device if it's available.

	Returns:
	Mesh: the loaded Mesh object.
	"""
	# obj supports face uv
	if path.endswith(".obj"):
	mesh = cls.load_obj(path, **kwargs)
	# trimesh only supports vertex uv, but can load more formats
	else:
	mesh = cls.load_trimesh(path, **kwargs)

	# clean
	if clean:
	from kiui.mesh_utils import clean_mesh
	vertices = mesh.v.detach().cpu().numpy()
	triangles = mesh.f.detach().cpu().numpy()
	vertices, triangles = clean_mesh(vertices, triangles, remesh=False)
	mesh.v = torch.from_numpy(vertices).contiguous().float().to(mesh.device)
	mesh.f = torch.from_numpy(triangles).contiguous().int().to(mesh.device)

	print(f"[Mesh loading] v: {mesh.v.shape}, f: {mesh.f.shape}")
	# auto-normalize
	if resize:
	mesh.auto_size(bound=bound)
	# auto-fix normal
	if renormal or mesh.vn is None:
	mesh.auto_normal()
	print(f"[Mesh loading] vn: {mesh.vn.shape}, fn: {mesh.fn.shape}")
	# auto-fix texcoords
	if retex or (mesh.albedo is not None and mesh.vt is None):
	mesh.auto_uv(cache_path=path)
	print(f"[Mesh loading] vt: {mesh.vt.shape}, ft: {mesh.ft.shape}")

	# rotate front dir to +z
	if front_dir != "+z":
	# axis switch
	if "-z" in front_dir:
	T = torch.tensor([[1, 0, 0], [0, 1, 0], [0, 0, -1]], device=mesh.device, dtype=torch.float32)
	elif "+x" in front_dir:
	T = torch.tensor([[0, 0, 1], [0, 1, 0], [1, 0, 0]], device=mesh.device, dtype=torch.float32)
	elif "-x" in front_dir:
	T = torch.tensor([[0, 0, -1], [0, 1, 0], [1, 0, 0]], device=mesh.device, dtype=torch.float32)
	elif "+y" in front_dir:
	T = torch.tensor([[1, 0, 0], [0, 0, 1], [0, 1, 0]], device=mesh.device, dtype=torch.float32)
	elif "-y" in front_dir:
	T = torch.tensor([[1, 0, 0], [0, 0, -1], [0, 1, 0]], device=mesh.device, dtype=torch.float32)
	else:
	T = torch.tensor([[1, 0, 0], [0, 1, 0], [0, 0, 1]], device=mesh.device, dtype=torch.float32)
	# rotation (how many 90 degrees)
	if '1' in front_dir:
	T @= torch.tensor([[0, -1, 0], [1, 0, 0], [0, 0, 1]], device=mesh.device, dtype=torch.float32)
	elif '2' in front_dir:
	T @= torch.tensor([[1, 0, 0], [0, -1, 0], [0, 0, 1]], device=mesh.device, dtype=torch.float32)
	elif '3' in front_dir:
	T @= torch.tensor([[0, 1, 0], [-1, 0, 0], [0, 0, 1]], device=mesh.device, dtype=torch.float32)
	mesh.v @= T
	mesh.vn @= T

	return mesh

	# load from obj file
	@classmethod
	def load_obj(cls, path, albedo_path=None, device=None):
	"""load an ``obj`` mesh.

	Args:
	path (str): path to mesh.
	albedo_path (str, optional): path to the albedo texture image, will overwrite the existing texture path if specified in mtl. Defaults to None.
	device (torch.device, optional): torch device. Defaults to None.

	Note:
	We will try to read `mtl` path from `obj`, else we assume the file name is the same as `obj` but with `mtl` extension.
	The `usemtl` statement is ignored, and we only use the last material path in `mtl` file.

	Returns:
	Mesh: the loaded Mesh object.
	"""
	assert os.path.splitext(path)[-1] == ".obj"

	mesh = cls()

	# device
	if device is None:
	device = torch.device("cuda" if torch.cuda.is_available() else "cpu")

	mesh.device = device

	# load obj
	with open(path, "r") as f:
	lines = f.readlines()

	def parse_f_v(fv):
	# pass in a vertex term of a face, return {v, vt, vn} (-1 if not provided)
	# supported forms:
	# f v1 v2 v3
	# f v1/vt1 v2/vt2 v3/vt3
	# f v1/vt1/vn1 v2/vt2/vn2 v3/vt3/vn3
	# f v1//vn1 v2//vn2 v3//vn3
	xs = [int(x) - 1 if x != "" else -1 for x in fv.split("/")]
	xs.extend([-1] * (3 - len(xs)))
	return xs[0], xs[1], xs[2]

	vertices, texcoords, normals = [], [], []
	faces, tfaces, nfaces = [], [], []
	mtl_path = None

	for line in lines:
	split_line = line.split()
	# empty line
	if len(split_line) == 0:
	continue
	prefix = split_line[0].lower()
	# mtllib
	if prefix == "mtllib":
	mtl_path = split_line[1]
	# usemtl
	elif prefix == "usemtl":
	pass # ignored
	# v/vn/vt
	elif prefix == "v":
	vertices.append([float(v) for v in split_line[1:]])
	elif prefix == "vn":
	normals.append([float(v) for v in split_line[1:]])
	elif prefix == "vt":
	val = [float(v) for v in split_line[1:]]
	texcoords.append([val[0], 1.0 - val[1]])
	elif prefix == "f":
	vs = split_line[1:]
	nv = len(vs)
	v0, t0, n0 = parse_f_v(vs[0])
	for i in range(nv - 2): # triangulate (assume vertices are ordered)
	v1, t1, n1 = parse_f_v(vs[i + 1])
	v2, t2, n2 = parse_f_v(vs[i + 2])
	faces.append([v0, v1, v2])
	tfaces.append([t0, t1, t2])
	nfaces.append([n0, n1, n2])

	mesh.v = torch.tensor(vertices, dtype=torch.float32, device=device)
	mesh.vt = (
	torch.tensor(texcoords, dtype=torch.float32, device=device)
	if len(texcoords) > 0
	else None
	)
	mesh.vn = (
	torch.tensor(normals, dtype=torch.float32, device=device)
	if len(normals) > 0
	else None
	)

	mesh.f = torch.tensor(faces, dtype=torch.int32, device=device)
	mesh.ft = (
	torch.tensor(tfaces, dtype=torch.int32, device=device)
	if len(texcoords) > 0
	else None
	)
	mesh.fn = (
	torch.tensor(nfaces, dtype=torch.int32, device=device)
	if len(normals) > 0
	else None
	)

	# see if there is vertex color
	use_vertex_color = False
	if mesh.v.shape[1] == 6:
	use_vertex_color = True
	mesh.vc = mesh.v[:, 3:]
	mesh.v = mesh.v[:, :3]
	print(f"[load_obj] use vertex color: {mesh.vc.shape}")

	# try to load texture image
	if not use_vertex_color:
	# try to retrieve mtl file
	mtl_path_candidates = []
	if mtl_path is not None:
	mtl_path_candidates.append(mtl_path)
	mtl_path_candidates.append(os.path.join(os.path.dirname(path), mtl_path))
	mtl_path_candidates.append(path.replace(".obj", ".mtl"))

	mtl_path = None
	for candidate in mtl_path_candidates:
	if os.path.exists(candidate):
	mtl_path = candidate
	break

	# if albedo_path is not provided, try retrieve it from mtl
	metallic_path = None
	roughness_path = None
	if mtl_path is not None and albedo_path is None:
	with open(mtl_path, "r") as f:
	lines = f.readlines()

	for line in lines:
	split_line = line.split()
	# empty line
	if len(split_line) == 0:
	continue
	prefix = split_line[0]

	if "map_Kd" in prefix:
	# assume relative path!
	albedo_path = os.path.join(os.path.dirname(path), split_line[1])
	print(f"[load_obj] use texture from: {albedo_path}")
	elif "map_Pm" in prefix:
	metallic_path = os.path.join(os.path.dirname(path), split_line[1])
	elif "map_Pr" in prefix:
	roughness_path = os.path.join(os.path.dirname(path), split_line[1])

	# still not found albedo_path, or the path doesn't exist
	if albedo_path is None or not os.path.exists(albedo_path):
	# init an empty texture
	print(f"[load_obj] init empty albedo!")
	# albedo = np.random.rand(1024, 1024, 3).astype(np.float32)
	albedo = np.ones((1024, 1024, 3), dtype=np.float32) * np.array([0.5, 0.5, 0.5]) # default color
	else:
	albedo = cv2.imread(albedo_path, cv2.IMREAD_UNCHANGED)
	albedo = cv2.cvtColor(albedo, cv2.COLOR_BGR2RGB)
	albedo = albedo.astype(np.float32) / 255
	print(f"[load_obj] load texture: {albedo.shape}")

	mesh.albedo = torch.tensor(albedo, dtype=torch.float32, device=device)

	# try to load metallic and roughness
	if metallic_path is not None and roughness_path is not None:
	print(f"[load_obj] load metallicRoughness from: {metallic_path}, {roughness_path}")
	metallic = cv2.imread(metallic_path, cv2.IMREAD_UNCHANGED)
	metallic = metallic.astype(np.float32) / 255
	roughness = cv2.imread(roughness_path, cv2.IMREAD_UNCHANGED)
	roughness = roughness.astype(np.float32) / 255
	metallicRoughness = np.stack([np.zeros_like(metallic), roughness, metallic], axis=-1)

	mesh.metallicRoughness = torch.tensor(metallicRoughness, dtype=torch.float32, device=device).contiguous()

	return mesh

	@classmethod
	def load_trimesh(cls, path, device=None):
	"""load a mesh using ``trimesh.load()``.

	Can load various formats like ``glb`` and serves as a fallback.

	Note:
	We will try to merge all meshes if the glb contains more than one,
	but this may cause the texture to lose, since we only support one texture image!

	Args:
	path (str): path to the mesh file.
	device (torch.device, optional): torch device. Defaults to None.

	Returns:
	Mesh: the loaded Mesh object.
	"""
	mesh = cls()

	# device
	if device is None:
	device = torch.device("cuda" if torch.cuda.is_available() else "cpu")

	mesh.device = device

	# use trimesh to load ply/glb
	_data = trimesh.load(path)
	if isinstance(_data, trimesh.Scene):
	if len(_data.geometry) == 1:
	_mesh = list(_data.geometry.values())[0]
	else:
	print(f"[load_trimesh] concatenating {len(_data.geometry)} meshes.")
	_concat = []
	# loop the scene graph and apply transform to each mesh
	scene_graph = _data.graph.to_flattened() # dict {name: {transform: 4x4 mat, geometry: str}}
	for k, v in scene_graph.items():
	name = v['geometry']
	if name in _data.geometry and isinstance(_data.geometry[name], trimesh.Trimesh):
	transform = v['transform']
	_concat.append(_data.geometry[name].apply_transform(transform))
	_mesh = trimesh.util.concatenate(_concat)
	else:
	_mesh = _data

	if _mesh.visual.kind == 'vertex':
	vertex_colors = _mesh.visual.vertex_colors
	vertex_colors = np.array(vertex_colors[..., :3]).astype(np.float32) / 255
	mesh.vc = torch.tensor(vertex_colors, dtype=torch.float32, device=device)
	print(f"[load_trimesh] use vertex color: {mesh.vc.shape}")
	elif _mesh.visual.kind == 'texture':
	_material = _mesh.visual.material
	if isinstance(_material, trimesh.visual.material.PBRMaterial):
	texture = np.array(_material.baseColorTexture).astype(np.float32) / 255
	# load metallicRoughness if present
	if _material.metallicRoughnessTexture is not None:
	metallicRoughness = np.array(_material.metallicRoughnessTexture).astype(np.float32) / 255
	mesh.metallicRoughness = torch.tensor(metallicRoughness, dtype=torch.float32, device=device).contiguous()
	elif isinstance(_material, trimesh.visual.material.SimpleMaterial):
	texture = np.array(_material.to_pbr().baseColorTexture).astype(np.float32) / 255
	else:
	raise NotImplementedError(f"material type {type(_material)} not supported!")
	mesh.albedo = torch.tensor(texture[..., :3], dtype=torch.float32, device=device).contiguous()
	print(f"[load_trimesh] load texture: {texture.shape}")
	else:
	texture = np.ones((1024, 1024, 3), dtype=np.float32) * np.array([0.5, 0.5, 0.5])
	mesh.albedo = torch.tensor(texture, dtype=torch.float32, device=device)
	print(f"[load_trimesh] failed to load texture.")

	vertices = _mesh.vertices

	try:
	texcoords = _mesh.visual.uv
	texcoords[:, 1] = 1 - texcoords[:, 1]
	except Exception as e:
	texcoords = None

	try:
	normals = _mesh.vertex_normals
	except Exception as e:
	normals = None

	# trimesh only support vertex uv...
	faces = tfaces = nfaces = _mesh.faces

	mesh.v = torch.tensor(vertices, dtype=torch.float32, device=device)
	mesh.vt = (
	torch.tensor(texcoords, dtype=torch.float32, device=device)
	if texcoords is not None
	else None
	)
	mesh.vn = (
	torch.tensor(normals, dtype=torch.float32, device=device)
	if normals is not None
	else None
	)

	mesh.f = torch.tensor(faces, dtype=torch.int32, device=device)
	mesh.ft = (
	torch.tensor(tfaces, dtype=torch.int32, device=device)
	if texcoords is not None
	else None
	)
	mesh.fn = (
	torch.tensor(nfaces, dtype=torch.int32, device=device)
	if normals is not None
	else None
	)

	return mesh

	# sample surface (using trimesh)
	def sample_surface(self, count: int):
	"""sample points on the surface of the mesh.

	Args:
	count (int): number of points to sample.

	Returns:
	torch.Tensor: the sampled points, float [count, 3].
	"""
	_mesh = trimesh.Trimesh(vertices=self.v.detach().cpu().numpy(), faces=self.f.detach().cpu().numpy())
	points, face_idx = trimesh.sample.sample_surface(_mesh, count)
	points = torch.from_numpy(points).float().to(self.device)
	return points

	# aabb
	def aabb(self):
	"""get the axis-aligned bounding box of the mesh.

	Returns:
	Tuple[torch.Tensor]: the min xyz and max xyz of the mesh.
	"""
	return torch.min(self.v, dim=0).values, torch.max(self.v, dim=0).values

	# unit size
	@torch.no_grad()
	def auto_size(self, bound=0.9):
	"""auto resize the mesh.

	Args:
	bound (float, optional): resizing into ``[-bound, bound]^3``. Defaults to 0.9.
	"""
	vmin, vmax = self.aabb()
	self.ori_center = (vmax + vmin) / 2
	self.ori_scale = 2 * bound / torch.max(vmax - vmin).item()
	self.v = (self.v - self.ori_center) * self.ori_scale

	def auto_normal(self):
	"""auto calculate the vertex normals.
	"""
	i0, i1, i2 = self.f[:, 0].long(), self.f[:, 1].long(), self.f[:, 2].long()
	v0, v1, v2 = self.v[i0, :], self.v[i1, :], self.v[i2, :]

	face_normals = torch.cross(v1 - v0, v2 - v0)

	# Splat face normals to vertices
	vn = torch.zeros_like(self.v)
	vn.scatter_add_(0, i0[:, None].repeat(1, 3), face_normals)
	vn.scatter_add_(0, i1[:, None].repeat(1, 3), face_normals)
	vn.scatter_add_(0, i2[:, None].repeat(1, 3), face_normals)

	# Normalize, replace zero (degenerated) normals with some default value
	vn = torch.where(
	dot(vn, vn) > 1e-20,
	vn,
	torch.tensor([0.0, 0.0, 1.0], dtype=torch.float32, device=vn.device),
	)
	vn = safe_normalize(vn)

	self.vn = vn
	self.fn = self.f

	def auto_uv(self, cache_path=None, vmap=True):
	"""auto calculate the uv coordinates.

	Args:
	cache_path (str, optional): path to save/load the uv cache as a npz file, this can avoid calculating uv every time when loading the same mesh, which is time-consuming. Defaults to None.
	vmap (bool, optional): remap vertices based on uv coordinates, so each v correspond to a unique vt (necessary for formats like gltf).
	Usually this will duplicate the vertices on the edge of uv atlas. Defaults to True.
	"""
	# try to load cache
	if cache_path is not None:
	cache_path = os.path.splitext(cache_path)[0] + "_uv.npz"
	if cache_path is not None and os.path.exists(cache_path):
	data = np.load(cache_path)
	vt_np, ft_np, vmapping = data["vt"], data["ft"], data["vmapping"]
	else:
	import xatlas

	v_np = self.v.detach().cpu().numpy()
	f_np = self.f.detach().int().cpu().numpy()
	atlas = xatlas.Atlas()
	atlas.add_mesh(v_np, f_np)
	chart_options = xatlas.ChartOptions()
	# chart_options.max_iterations = 4
	atlas.generate(chart_options=chart_options)
	vmapping, ft_np, vt_np = atlas[0] # [N], [M, 3], [N, 2]

	# save to cache
	if cache_path is not None:
	np.savez(cache_path, vt=vt_np, ft=ft_np, vmapping=vmapping)

	vt = torch.from_numpy(vt_np.astype(np.float32)).to(self.device)
	ft = torch.from_numpy(ft_np.astype(np.int32)).to(self.device)
	self.vt = vt
	self.ft = ft

	if vmap:
	vmapping = torch.from_numpy(vmapping.astype(np.int64)).long().to(self.device)
	self.align_v_to_vt(vmapping)

	def align_v_to_vt(self, vmapping=None):
	""" remap v/f and vn/fn to vt/ft.

	Args:
	vmapping (np.ndarray, optional): the mapping relationship from f to ft. Defaults to None.
	"""
	if vmapping is None:
	ft = self.ft.view(-1).long()
	f = self.f.view(-1).long()
	vmapping = torch.zeros(self.vt.shape[0], dtype=torch.long, device=self.device)
	vmapping[ft] = f # scatter, randomly choose one if index is not unique

	self.v = self.v[vmapping]
	self.f = self.ft

	if self.vn is not None:
	self.vn = self.vn[vmapping]
	self.fn = self.ft

	def to(self, device):
	"""move all tensor attributes to device.

	Args:
	device (torch.device): target device.

	Returns:
	Mesh: self.
	"""
	self.device = device
	for name in ["v", "f", "vn", "fn", "vt", "ft", "albedo", "vc", "metallicRoughness"]:
	tensor = getattr(self, name)
	if tensor is not None:
	setattr(self, name, tensor.to(device))
	return self

	def write(self, path):
	"""write the mesh to a path.

	Args:
	path (str): path to write, supports ply, obj and glb.
	"""
	if path.endswith(".ply"):
	self.write_ply(path)
	elif path.endswith(".obj"):
	self.write_obj(path)
	elif path.endswith(".glb") or path.endswith(".gltf"):
	self.write_glb(path)
	else:
	raise NotImplementedError(f"format {path} not supported!")

	def write_ply(self, path):
	"""write the mesh in ply format. Only for geometry!

	Args:
	path (str): path to write.
	"""

	if self.albedo is not None:
	print(f'[WARN] ply format does not support exporting texture, will ignore!')

	v_np = self.v.detach().cpu().numpy()
	f_np = self.f.detach().cpu().numpy()

	_mesh = trimesh.Trimesh(vertices=v_np, faces=f_np)
	_mesh.export(path)


	def write_glb(self, path):
	"""write the mesh in glb/gltf format.
	This will create a scene with a single mesh.

	Args:
	path (str): path to write.
	"""

	# assert self.v.shape[0] == self.vn.shape[0] and self.v.shape[0] == self.vt.shape[0]
	if self.vt is not None and self.v.shape[0] != self.vt.shape[0]:
	self.align_v_to_vt()

	import pygltflib

	f_np = self.f.detach().cpu().numpy().astype(np.uint32)
	f_np_blob = f_np.flatten().tobytes()

	v_np = self.v.detach().cpu().numpy().astype(np.float32)
	v_np_blob = v_np.tobytes()

	blob = f_np_blob + v_np_blob
	byteOffset = len(blob)

	# base mesh
	gltf = pygltflib.GLTF2(
	scene=0,
	scenes=[pygltflib.Scene(nodes=[0])],
	nodes=[pygltflib.Node(mesh=0)],
	meshes=[pygltflib.Mesh(primitives=[pygltflib.Primitive(
	# indices to accessors (0 is triangles)
	attributes=pygltflib.Attributes(
	POSITION=1,
	),
	indices=0,
	)])],
	buffers=[
	pygltflib.Buffer(byteLength=len(f_np_blob) + len(v_np_blob))
	],
	# buffer view (based on dtype)
	bufferViews=[
	# triangles; as flatten (element) array
	pygltflib.BufferView(
	buffer=0,
	byteLength=len(f_np_blob),
	target=pygltflib.ELEMENT_ARRAY_BUFFER, # GL_ELEMENT_ARRAY_BUFFER (34963)
	),
	# positions; as vec3 array
	pygltflib.BufferView(
	buffer=0,
	byteOffset=len(f_np_blob),
	byteLength=len(v_np_blob),
	byteStride=12, # vec3
	target=pygltflib.ARRAY_BUFFER, # GL_ARRAY_BUFFER (34962)
	),
	],
	accessors=[
	# 0 = triangles
	pygltflib.Accessor(
	bufferView=0,
	componentType=pygltflib.UNSIGNED_INT, # GL_UNSIGNED_INT (5125)
	count=f_np.size,
	type=pygltflib.SCALAR,
	max=[int(f_np.max())],
	min=[int(f_np.min())],
	),
	# 1 = positions
	pygltflib.Accessor(
	bufferView=1,
	componentType=pygltflib.FLOAT, # GL_FLOAT (5126)
	count=len(v_np),
	type=pygltflib.VEC3,
	max=v_np.max(axis=0).tolist(),
	min=v_np.min(axis=0).tolist(),
	),
	],
	)

	# append texture info
	if self.vt is not None:

	vt_np = self.vt.detach().cpu().numpy().astype(np.float32)
	vt_np_blob = vt_np.tobytes()

	albedo = self.albedo.detach().cpu().numpy()
	albedo = (albedo * 255).astype(np.uint8)
	albedo = cv2.cvtColor(albedo, cv2.COLOR_RGB2BGR)
	albedo_blob = cv2.imencode('.png', albedo)[1].tobytes()

	# update primitive
	gltf.meshes[0].primitives[0].attributes.TEXCOORD_0 = 2
	gltf.meshes[0].primitives[0].material = 0

	# update materials
	gltf.materials.append(pygltflib.Material(
	pbrMetallicRoughness=pygltflib.PbrMetallicRoughness(
	baseColorTexture=pygltflib.TextureInfo(index=0, texCoord=0),
	metallicFactor=0.0,
	roughnessFactor=1.0,
	),
	alphaMode=pygltflib.OPAQUE,
	alphaCutoff=None,
	doubleSided=True,
	))

	gltf.textures.append(pygltflib.Texture(sampler=0, source=0))
	gltf.samplers.append(pygltflib.Sampler(magFilter=pygltflib.LINEAR, minFilter=pygltflib.LINEAR_MIPMAP_LINEAR, wrapS=pygltflib.REPEAT, wrapT=pygltflib.REPEAT))
	gltf.images.append(pygltflib.Image(bufferView=3, mimeType="image/png"))

	# update buffers
	gltf.bufferViews.append(
	# index = 2, texcoords; as vec2 array
	pygltflib.BufferView(
	buffer=0,
	byteOffset=byteOffset,
	byteLength=len(vt_np_blob),
	byteStride=8, # vec2
	target=pygltflib.ARRAY_BUFFER,
	)
	)

	gltf.accessors.append(
	# 2 = texcoords
	pygltflib.Accessor(
	bufferView=2,
	componentType=pygltflib.FLOAT,
	count=len(vt_np),
	type=pygltflib.VEC2,
	max=vt_np.max(axis=0).tolist(),
	min=vt_np.min(axis=0).tolist(),
	)
	)

	blob += vt_np_blob
	byteOffset += len(vt_np_blob)

	gltf.bufferViews.append(
	# index = 3, albedo texture; as none target
	pygltflib.BufferView(
	buffer=0,
	byteOffset=byteOffset,
	byteLength=len(albedo_blob),
	)
	)

	blob += albedo_blob
	byteOffset += len(albedo_blob)

	gltf.buffers[0].byteLength = byteOffset

	# append metllic roughness
	if self.metallicRoughness is not None:
	metallicRoughness = self.metallicRoughness.detach().cpu().numpy()
	metallicRoughness = (metallicRoughness * 255).astype(np.uint8)
	metallicRoughness = cv2.cvtColor(metallicRoughness, cv2.COLOR_RGB2BGR)
	metallicRoughness_blob = cv2.imencode('.png', metallicRoughness)[1].tobytes()

	# update texture definition
	gltf.materials[0].pbrMetallicRoughness.metallicFactor = 1.0
	gltf.materials[0].pbrMetallicRoughness.roughnessFactor = 1.0
	gltf.materials[0].pbrMetallicRoughness.metallicRoughnessTexture = pygltflib.TextureInfo(index=1, texCoord=0)

	gltf.textures.append(pygltflib.Texture(sampler=1, source=1))
	gltf.samplers.append(pygltflib.Sampler(magFilter=pygltflib.LINEAR, minFilter=pygltflib.LINEAR_MIPMAP_LINEAR, wrapS=pygltflib.REPEAT, wrapT=pygltflib.REPEAT))
	gltf.images.append(pygltflib.Image(bufferView=4, mimeType="image/png"))

	# update buffers
	gltf.bufferViews.append(
	# index = 4, metallicRoughness texture; as none target
	pygltflib.BufferView(
	buffer=0,
	byteOffset=byteOffset,
	byteLength=len(metallicRoughness_blob),
	)
	)

	blob += metallicRoughness_blob
	byteOffset += len(metallicRoughness_blob)

	gltf.buffers[0].byteLength = byteOffset


	# set actual data
	gltf.set_binary_blob(blob)

	# glb = b"".join(gltf.save_to_bytes())
	gltf.save(path)


	def write_obj(self, path):
	"""write the mesh in obj format. Will also write the texture and mtl files.

	Args:
	path (str): path to write.
	"""

	mtl_path = path.replace(".obj", ".mtl")
	albedo_path = path.replace(".obj", "_albedo.png")
	metallic_path = path.replace(".obj", "_metallic.png")
	roughness_path = path.replace(".obj", "_roughness.png")

	v_np = self.v.detach().cpu().numpy()
	vt_np = self.vt.detach().cpu().numpy() if self.vt is not None else None
	vn_np = self.vn.detach().cpu().numpy() if self.vn is not None else None
	f_np = self.f.detach().cpu().numpy()
	ft_np = self.ft.detach().cpu().numpy() if self.ft is not None else None
	fn_np = self.fn.detach().cpu().numpy() if self.fn is not None else None

	with open(path, "w") as fp:
	fp.write(f"mtllib {os.path.basename(mtl_path)} \n")

	for v in v_np:
	fp.write(f"v {v[0]} {v[1]} {v[2]} \n")

	if vt_np is not None:
	for v in vt_np:
	fp.write(f"vt {v[0]} {1 - v[1]} \n")

	if vn_np is not None:
	for v in vn_np:
	fp.write(f"vn {v[0]} {v[1]} {v[2]} \n")

	fp.write(f"usemtl defaultMat \n")
	for i in range(len(f_np)):
	fp.write(
	f'f {f_np[i, 0] + 1}/{ft_np[i, 0] + 1 if ft_np is not None else ""}/{fn_np[i, 0] + 1 if fn_np is not None else ""} \
	{f_np[i, 1] + 1}/{ft_np[i, 1] + 1 if ft_np is not None else ""}/{fn_np[i, 1] + 1 if fn_np is not None else ""} \
	{f_np[i, 2] + 1}/{ft_np[i, 2] + 1 if ft_np is not None else ""}/{fn_np[i, 2] + 1 if fn_np is not None else ""} \n'
	)

	with open(mtl_path, "w") as fp:
	fp.write(f"newmtl defaultMat \n")
	fp.write(f"Ka 1 1 1 \n")
	fp.write(f"Kd 1 1 1 \n")
	fp.write(f"Ks 0 0 0 \n")
	fp.write(f"Tr 1 \n")
	fp.write(f"illum 1 \n")
	fp.write(f"Ns 0 \n")
	if self.albedo is not None:
	fp.write(f"map_Kd {os.path.basename(albedo_path)} \n")
	if self.metallicRoughness is not None:
	# ref: https://en.wikipedia.org/wiki/Wavefront_.obj_file#Physically-based_Rendering
	fp.write(f"map_Pm {os.path.basename(metallic_path)} \n")
	fp.write(f"map_Pr {os.path.basename(roughness_path)} \n")

	if self.albedo is not None:
	albedo = self.albedo.detach().cpu().numpy()
	albedo = (albedo * 255).astype(np.uint8)
	cv2.imwrite(albedo_path, cv2.cvtColor(albedo, cv2.COLOR_RGB2BGR))

	if self.metallicRoughness is not None:
	metallicRoughness = self.metallicRoughness.detach().cpu().numpy()
	metallicRoughness = (metallicRoughness * 255).astype(np.uint8)
	cv2.imwrite(metallic_path, metallicRoughness[..., 2])
	cv2.imwrite(roughness_path, metallicRoughness[..., 1])