Bug in culling: The size of tensor a (3) must match the size of tensor b (XXX) at non-singleton dimension 1

[Algomorph]

Instructions To Reproduce the Issue:

Try running this code:

import numpy as np
import pytorch3d.utils
from pytorch3d.renderer.cameras import PerspectiveCameras
from pytorch3d.renderer.mesh import MeshRasterizer, RasterizationSettings
import torch

intrinsic_matrix = np.array([[575.548, 0.,     323.172, 0.],
                             [0.,      577.46, 236.417, 0.],
                             [0.,      0.,     1.,      0.],
                             [0.,      0., 0., 1.        ]])
intrinsic_matrix_torch = torch.from_numpy(intrinsic_matrix).cuda().unsqueeze(0)

torch_device = torch.device("cuda:0")
meshes_torch3d = pytorch3d.utils.torus(20.0, 85.0, 32, 16, device=torch_device)
image_size = (480, 640)

camera_rotation = torch.eye(3, dtype=torch.float32, device=torch_device)[None]  # (1, 3, 3)
camera_translation = torch.zeros(1, 3, dtype=torch.float32, device=torch_device)  # (1, 3)

cameras = PerspectiveCameras(device=torch_device,
                             R=camera_rotation,
                             T=camera_translation,
                             K=intrinsic_matrix_torch,
                             image_size=[image_size])

rasterization_settings = RasterizationSettings(image_size=image_size, cull_backfaces=True, cull_to_frustum=True)
rasterizer = MeshRasterizer(cameras, raster_settings=rasterization_settings)
fragments = rasterizer.forward(meshes_torch3d)

The output will be:

Traceback (most recent call last):
  File "/home/algomorph/Workbench/NeuralTracking/pipeline/rendering_test.py", line 51, in <module>
    sys.exit(main())
  File "/home/algomorph/Workbench/NeuralTracking/pipeline/rendering_test.py", line 44, in main
    fragments = rasterizer.forward(meshes_torch3d)
  File "/home/algomorph/.local/lib/python3.8/site-packages/pytorch3d/renderer/mesh/rasterizer.py", line 164, in forward
    pix_to_face, zbuf, bary_coords, dists = rasterize_meshes(
  File "/home/algomorph/.local/lib/python3.8/site-packages/pytorch3d/renderer/mesh/rasterize_meshes.py", line 175, in rasterize_meshes
    clipped_faces = clip_faces(
  File "/home/algomorph/.local/lib/python3.8/site-packages/pytorch3d/renderer/mesh/clip.py", line 400, in clip_faces
    cases1_unclipped = (faces_num_clipped_verts == 0) & faces_unculled
RuntimeError: The size of tensor a (3) must match the size of tensor b (1024) at non-singleton dimension 1

Version info:
pytorch3d built from commit cc08c6b (from this this morning)
pytorch3d.version : '0.4.0'
torch.version: '1.7.0a0+57bffc3' ( == 1.7.1 release, built from source)
torch.version.cuda: '11.1'
Python: 3.8.5
OS: Ubuntu 20.04

[Algomorph]

I'm guessing this line here is the source of the bug:

pytorch3d/pytorch3d/renderer/mesh/clip.py

Line 375 in 7c0d307

faces_num_clipped_verts = torch.zeros([F, 3], device=device)

Should be instead:

faces_num_clipped_verts = torch.zeros([F], device=device)

[nikhilaravi]

This should now be fixed by a0f7931.