trellis/representations/mesh/flexicubes/examples/optimize.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.
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import argparse
import numpy as np
import torch
import nvdiffrast.torch as dr
import trimesh
import os
from util import *
import render
import loss
import imageio

import sys
sys.path.append('..')
from flexicubes import FlexiCubes

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

def lr_schedule(iter):
    return max(0.0, 10**(-(iter)*0.0002)) # Exponential falloff from [1.0, 0.1] over 5k epochs.    

if __name__ == "__main__":
    parser = argparse.ArgumentParser(description='flexicubes optimization')
    parser.add_argument('-o', '--out_dir', type=str, default=None)
    parser.add_argument('-rm', '--ref_mesh', type=str)    
    
    parser.add_argument('-i', '--iter', type=int, default=1000)
    parser.add_argument('-b', '--batch', type=int, default=8)
    parser.add_argument('-r', '--train_res', nargs=2, type=int, default=[2048, 2048])
    parser.add_argument('-lr', '--learning_rate', type=float, default=0.01)
    parser.add_argument('--voxel_grid_res', type=int, default=64)
    
    parser.add_argument('--sdf_loss', type=bool, default=True)
    parser.add_argument('--develop_reg', type=bool, default=False)
    parser.add_argument('--sdf_regularizer', type=float, default=0.2)
    
    parser.add_argument('-dr', '--display_res', nargs=2, type=int, default=[512, 512])
    parser.add_argument('-si', '--save_interval', type=int, default=20)
    FLAGS = parser.parse_args()
    device = 'cuda'
    
    os.makedirs(FLAGS.out_dir, exist_ok=True)
    glctx = dr.RasterizeGLContext()
    
    # Load GT mesh
    gt_mesh = load_mesh(FLAGS.ref_mesh, device)
    gt_mesh.auto_normals() # compute face normals for visualization
    
    # ==============================================================================================
    #  Create and initialize FlexiCubes
    # ==============================================================================================
    fc = FlexiCubes(device)
    x_nx3, cube_fx8 = fc.construct_voxel_grid(FLAGS.voxel_grid_res)
    x_nx3 *= 2 # scale up the grid so that it's larger than the target object
    
    sdf = torch.rand_like(x_nx3[:,0]) - 0.1 # randomly init SDF
    sdf    = torch.nn.Parameter(sdf.clone().detach(), requires_grad=True)
    # set per-cube learnable weights to zeros
    weight = torch.zeros((cube_fx8.shape[0], 21), dtype=torch.float, device='cuda') 
    weight    = torch.nn.Parameter(weight.clone().detach(), requires_grad=True)
    deform = torch.nn.Parameter(torch.zeros_like(x_nx3), requires_grad=True)
    
    #  Retrieve all the edges of the voxel grid; these edges will be utilized to 
    #  compute the regularization loss in subsequent steps of the process.    
    all_edges = cube_fx8[:, fc.cube_edges].reshape(-1, 2)
    grid_edges = torch.unique(all_edges, dim=0)
    
    # ==============================================================================================
    #  Setup optimizer
    # ==============================================================================================
    optimizer = torch.optim.Adam([sdf, weight,deform], lr=FLAGS.learning_rate)
    scheduler = torch.optim.lr_scheduler.LambdaLR(optimizer, lr_lambda=lambda x: lr_schedule(x)) 
    
    # ==============================================================================================
    #  Train loop
    # ==============================================================================================   
    for it in range(FLAGS.iter): 
        optimizer.zero_grad()
        # sample random camera poses
        mv, mvp = render.get_random_camera_batch(FLAGS.batch, iter_res=FLAGS.train_res, device=device, use_kaolin=False)
        # render gt mesh
        target = render.render_mesh_paper(gt_mesh, mv, mvp, FLAGS.train_res)
        # extract and render FlexiCubes mesh
        grid_verts = x_nx3 + (2-1e-8) / (FLAGS.voxel_grid_res * 2) * torch.tanh(deform)
        vertices, faces, L_dev = fc(grid_verts, sdf, cube_fx8, FLAGS.voxel_grid_res, beta_fx12=weight[:,:12], alpha_fx8=weight[:,12:20],
            gamma_f=weight[:,20], training=True)
        flexicubes_mesh = Mesh(vertices, faces)
        buffers = render.render_mesh_paper(flexicubes_mesh, mv, mvp, FLAGS.train_res)
        
        # evaluate reconstruction loss
        mask_loss = (buffers['mask'] - target['mask']).abs().mean()
        depth_loss = (((((buffers['depth'] - (target['depth']))* target['mask'])**2).sum(-1)+1e-8)).sqrt().mean() * 10
    
        t_iter = it / FLAGS.iter
        sdf_weight = FLAGS.sdf_regularizer - (FLAGS.sdf_regularizer - FLAGS.sdf_regularizer/20)*min(1.0, 4.0 * t_iter)
        reg_loss = loss.sdf_reg_loss(sdf, grid_edges).mean() * sdf_weight # Loss to eliminate internal floaters that are not visible
        reg_loss += L_dev.mean() * 0.5
        reg_loss += (weight[:,:20]).abs().mean() * 0.1
        total_loss = mask_loss + depth_loss + reg_loss
        
        if FLAGS.sdf_loss: # optionally add SDF loss to eliminate internal structures
            with torch.no_grad():
                pts = sample_random_points(1000, gt_mesh)
                gt_sdf = compute_sdf(pts, gt_mesh.vertices, gt_mesh.faces)
            pred_sdf = compute_sdf(pts, flexicubes_mesh.vertices, flexicubes_mesh.faces)
            total_loss += torch.nn.functional.mse_loss(pred_sdf, gt_sdf) * 2e3
        
        # optionally add developability regularizer, as described in paper section 5.2
        if FLAGS.develop_reg:
            reg_weight = max(0, t_iter - 0.8) * 5
            if reg_weight > 0: # only applied after shape converges
                reg_loss = loss.mesh_developable_reg(flexicubes_mesh).mean() * 10
                reg_loss += (deform).abs().mean()
                reg_loss += (weight[:,:20]).abs().mean()
                total_loss = mask_loss + depth_loss + reg_loss 
        
        total_loss.backward()
        optimizer.step()
        scheduler.step()        
        
        if (it % FLAGS.save_interval == 0 or it == (FLAGS.iter-1)): # save normal image for visualization
            with torch.no_grad():
                # extract mesh with training=False
                vertices, faces, L_dev = fc(grid_verts, sdf, cube_fx8, FLAGS.voxel_grid_res, beta_fx12=weight[:,:12], alpha_fx8=weight[:,12:20],
                gamma_f=weight[:,20], training=False)
                flexicubes_mesh = Mesh(vertices, faces)
                
                flexicubes_mesh.auto_normals() # compute face normals for visualization
                mv, mvp = render.get_rotate_camera(it//FLAGS.save_interval, iter_res=FLAGS.display_res, device=device,use_kaolin=False)
                val_buffers = render.render_mesh_paper(flexicubes_mesh, mv.unsqueeze(0), mvp.unsqueeze(0), FLAGS.display_res, return_types=["normal"], white_bg=True)
                val_image = ((val_buffers["normal"][0].detach().cpu().numpy()+1)/2*255).astype(np.uint8)
                
                gt_buffers = render.render_mesh_paper(gt_mesh, mv.unsqueeze(0), mvp.unsqueeze(0), FLAGS.display_res, return_types=["normal"], white_bg=True)
                gt_image = ((gt_buffers["normal"][0].detach().cpu().numpy()+1)/2*255).astype(np.uint8)
                imageio.imwrite(os.path.join(FLAGS.out_dir, '{:04d}.png'.format(it)), np.concatenate([val_image, gt_image], 1))
                print(f"Optimization Step [{it}/{FLAGS.iter}], Loss: {total_loss.item():.4f}")
            
    # ==============================================================================================
    #  Save ouput
    # ==============================================================================================     
    mesh_np = trimesh.Trimesh(vertices = vertices.detach().cpu().numpy(), faces=faces.detach().cpu().numpy(), process=False)
    mesh_np.export(os.path.join(FLAGS.out_dir, 'output_mesh.obj'))