Staircase effect observed during Shape VAE reconstruction

Hello,

I am currently testing the Shape VAE reconstruction using the TRELLIS-2 models, but I am encountering a staircase (blocky) effect on the generated surfaces.

Specifically, I compared the two pipelines:

mesh -> ovoxel -> mesh: Direct reconstruction works perfectly and produces a smooth surface.

mesh -> ovoxel -> VAE -> mesh: Passing the data through the VAE encoder and decoder results in severe staircase artifacts, as shown in the attached image.

Here is the inference code I am currently using:

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## Load Encoder
    # Download config and safetensors from hf
    encoder_cfg = hf_hub_download(repo_id="microsoft/TRELLIS.2-4B", filename="ckpts/shape_enc_next_dc_f16c32_fp16.json")
    encoder_weights = hf_hub_download(repo_id="microsoft/TRELLIS.2-4B", filename="ckpts/shape_enc_next_dc_f16c32_fp16.safetensors")    
    with open(encoder_cfg) as f:
        encoder_args = json.load(f)["args"]
    encoder = FlexiDualGridVaeEncoder(**encoder_args)
    state_dict = load_file(encoder_weights)
    encoder.load_state_dict(state_dict)
    encoder.eval()
    encoder.cuda()

    ## Load Decoder
    decoder_cfg = hf_hub_download(repo_id="microsoft/TRELLIS.2-4B", filename="ckpts/shape_dec_next_dc_f16c32_fp16.json")
    decoder_weights = hf_hub_download(repo_id="microsoft/TRELLIS.2-4B", filename="ckpts/shape_dec_next_dc_f16c32_fp16.safetensors")    
    with open(decoder_cfg) as f:
        decoder_args = json.load(f)["args"]
    # decoder_args["use_fp16"] = False

        
    decoder = FlexiDualGridVaeDecoder(**decoder_args)
    state_dict = load_file(decoder_weights)
    decoder.load_state_dict(state_dict)
    decoder.eval()
    decoder.cuda()


    RES = 512
    decoder.set_resolution(RES)

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      asset = trimesh.load(gt_path)
      mesh = asset.to_mesh()
      mesh = normalize_mesh(mesh)

      # Convert to o-voxel
      vertices = torch.from_numpy(mesh.vertices).float()
      faces = torch.from_numpy(mesh.faces).long()

      voxel_indices, dual_vertices, intersected = o_voxel.convert.mesh_to_flexible_dual_grid(
          vertices, faces,
          grid_size=RES,                              # Resolution
          aabb=[[-0.5,-0.5,-0.5],[0.5,0.5,0.5]],      # Axis-aligned bounding box
          face_weight=1.0,                            # Face term weight in QEF
          boundary_weight=0.2,                        # Boundary term weight in QEF
          regularization_weight=1e-2,                 # Regularization term weight in QEF
          timing=True
      )

      coords = voxel_indices

      local_dual_vertices = dual_vertices

      #  Inference VAE
      batch_idx = torch.zeros((coords.shape[0], 1), dtype=torch.int32, device='cuda')
      sp_coords = torch.cat([batch_idx, coords.cuda()], dim=1)

      sp_vertices = sp.SparseTensor(
          feats=local_dual_vertices.cuda().float(),
          coords=sp_coords
      )
      sp_intersected = sp.SparseTensor(
          feats=intersected.cuda().float(), 
          coords=sp_coords
      )        
      with torch.no_grad():            
          latent = encoder(sp_vertices, sp_intersected, sample_posterior=False)        
          recon_output = decoder(latent)            

      output_mesh = recon_output[0]
      
      rec_verts = output_mesh.vertices
      rec_faces = output_mesh.faces        

      recon_mesh = trimesh.Trimesh(vertices=rec_verts.detach().cpu().numpy(), faces=rec_faces.detach().cpu().numpy())
      recon_mesh.export( output_path / f"{gt_path.stem}.obj")

Could you please let me know if I am missing something or if there are any specific modifications needed in my inference code (such as tensor precision, coordinate types, or scaling) to resolve this issue?

Thank you for your time and for sharing this amazing work!

Start by comparing the direct mesh -> ovoxel -> mesh path with the VAE path around mesh_to_flexible_dual_grid, FlexiDualGridVaeEncoder, and FlexiDualGridVaeDecoder at RES 512. Reproduce the staircase artifact while checking the precision, coordinate types, and scaling values shown in the inference code. Done means identifying the inference mismatch or confirming a required modification that removes the artifact.