trellis/representations/mesh/flexicubes/examples/util.py

# Copyright (c) 2025 NVIDIA CORPORATION & AFFILIATES.
# All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import numpy as np
import torch
import trimesh
import kaolin
import nvdiffrast.torch as dr

###############################################################################
# Functions adapted from https://github.com/NVlabs/nvdiffrec
###############################################################################

def dot(x: torch.Tensor, y: torch.Tensor) -> torch.Tensor:
    return torch.sum(x*y, -1, keepdim=True)

def length(x: torch.Tensor, eps: float =1e-8) -> torch.Tensor:
    return torch.sqrt(torch.clamp(dot(x,x), min=eps)) # Clamp to avoid nan gradients because grad(sqrt(0)) = NaN

def safe_normalize(x: torch.Tensor, eps: float =1e-8) -> torch.Tensor:
    return x / length(x, eps)

def perspective(fovy=0.7854, aspect=1.0, n=0.1, f=1000.0, device=None):
    y = np.tan(fovy / 2)
    return torch.tensor([[1/(y*aspect),    0,            0,              0], 
                         [           0, 1/-y,            0,              0], 
                         [           0,    0, -(f+n)/(f-n), -(2*f*n)/(f-n)], 
                         [           0,    0,           -1,              0]], dtype=torch.float32, device=device)

def translate(x, y, z, device=None):
    return torch.tensor([[1, 0, 0, x], 
                         [0, 1, 0, y], 
                         [0, 0, 1, z], 
                         [0, 0, 0, 1]], dtype=torch.float32, device=device)

@torch.no_grad()
def random_rotation_translation(t, device=None):
    m = np.random.normal(size=[3, 3])
    m[1] = np.cross(m[0], m[2])
    m[2] = np.cross(m[0], m[1])
    m = m / np.linalg.norm(m, axis=1, keepdims=True)
    m = np.pad(m, [[0, 1], [0, 1]], mode='constant')
    m[3, 3] = 1.0
    m[:3, 3] = np.random.uniform(-t, t, size=[3])
    return torch.tensor(m, dtype=torch.float32, device=device)

def rotate_x(a, device=None):
    s, c = np.sin(a), np.cos(a)
    return torch.tensor([[1,  0, 0, 0], 
                         [0,  c, s, 0], 
                         [0, -s, c, 0], 
                         [0,  0, 0, 1]], dtype=torch.float32, device=device)

def rotate_y(a, device=None):
    s, c = np.sin(a), np.cos(a)
    return torch.tensor([[ c, 0, s, 0], 
                         [ 0, 1, 0, 0], 
                         [-s, 0, c, 0], 
                         [ 0, 0, 0, 1]], dtype=torch.float32, device=device)
    
class Mesh:
    def __init__(self, vertices, faces):
        self.vertices = vertices
        self.faces = faces
        
    def auto_normals(self):
        v0 = self.vertices[self.faces[:, 0], :]
        v1 = self.vertices[self.faces[:, 1], :]
        v2 = self.vertices[self.faces[:, 2], :]
        nrm = safe_normalize(torch.cross(v1 - v0, v2 - v0))
        self.nrm = nrm

def load_mesh(path, device):
    mesh_np = trimesh.load(path)
    vertices = torch.tensor(mesh_np.vertices, device=device, dtype=torch.float)
    faces = torch.tensor(mesh_np.faces, device=device, dtype=torch.long)
    
    # Normalize
    vmin, vmax = vertices.min(dim=0)[0], vertices.max(dim=0)[0]
    scale = 1.8 / torch.max(vmax - vmin).item()
    vertices = vertices - (vmax + vmin) / 2 # Center mesh on origin
    vertices = vertices * scale # Rescale to [-0.9, 0.9]
    return Mesh(vertices, faces)

def compute_sdf(points, vertices, faces):
    face_vertices = kaolin.ops.mesh.index_vertices_by_faces(vertices.clone().unsqueeze(0), faces)
    distance = kaolin.metrics.trianglemesh.point_to_mesh_distance(points.unsqueeze(0), face_vertices)[0]
    with torch.no_grad():
        sign = (kaolin.ops.mesh.check_sign(vertices.unsqueeze(0), faces, points.unsqueeze(0))<1).float() * 2 - 1
    sdf = (sign*distance).squeeze(0)
    return sdf

def sample_random_points(n, mesh):
    pts_random = (torch.rand((n//2,3),device='cuda') - 0.5) * 2
    pts_surface = kaolin.ops.mesh.sample_points(mesh.vertices.unsqueeze(0), mesh.faces, 500)[0].squeeze(0)
    pts_surface += torch.randn_like(pts_surface) * 0.05
    pts = torch.cat([pts_random, pts_surface])
    return pts

def xfm_points(points, matrix):
    '''Transform points.
    Args:
        points: Tensor containing 3D points with shape [minibatch_size, num_vertices, 3] or [1, num_vertices, 3]
        matrix: A 4x4 transform matrix with shape [minibatch_size, 4, 4]
        use_python: Use PyTorch's torch.matmul (for validation)
    Returns:
        Transformed points in homogeneous 4D with shape [minibatch_size, num_vertices, 4].
    '''
    out = torch.matmul(
        torch.nn.functional.pad(points, pad=(0, 1), mode='constant', value=1.0), torch.transpose(matrix, 1, 2))
    if torch.is_anomaly_enabled():
        assert torch.all(torch.isfinite(out)), "Output of xfm_points contains inf or NaN"
    return out

def interpolate(attr, rast, attr_idx, rast_db=None):
    return dr.interpolate(
        attr, rast, attr_idx, rast_db=rast_db,
        diff_attrs=None if rast_db is None else 'all')