docstr: Case 4 triangles have exactly 1 vertex behind the clipping plane (z=0) so
  are clipped into a smaller quadrilateral and then divided into two triangles.
  
  Test with a single triangle parallel to the z axis which intersects with
  the image plane.
docstr_tok: ["Case","4","triangles","have","exactly","1","vertex","behind","the","clipping","plane","(","z=0",")","so","are","clipped","into","a","smaller","quadrilateral","and","then","divided","into","two","triangles",".","Test","with","a","single","triangle","parallel","to","the","z","axis","which","intersects","with","the","image","plane","."]
code: def test_case_4(self):
      """
      Case 4 triangles have exactly 1 vertex behind the clipping plane (z=0) so
      are clipped into a smaller quadrilateral and then divided into two triangles.
  
      Test with a single triangle parallel to the z axis which intersects with
      the image plane.
      """
  
      device = "cuda:0"
      verts = torch.tensor(
          [[0.0, 0.0, -1.0], [-1.0, 0.0, 1.0], [1.0, 0.0, 1.0]],
          dtype=torch.float32,
          device=device,
      )
      faces = torch.tensor(
          [
              [0, 1, 2],
          ],
          dtype=torch.int64,
          device=device,
      )
      meshes = Meshes(verts=[verts], faces=[faces])
      clipped_faces = self.clip_faces(meshes)
  
      clipped_face_verts = torch.tensor(
          [
              # t1
              [
                  [-0.5050, 0.0000, 0.0100],
                  [-1.0000, 0.0000, 1.0000],
                  [0.5050, 0.0000, 0.0100],
              ],
              # t2
              [
                  [0.5050, 0.0000, 0.0100],
                  [-1.0000, 0.0000, 1.0000],
                  [1.0000, 0.0000, 1.0000],
              ],
          ],
          device=device,
          dtype=torch.float32,
      )
  
      barycentric_conversion = torch.tensor(
          [
              [
                  [0.4950, 0.0000, 0.4950],
                  [0.5050, 1.0000, 0.0000],
                  [0.0000, 0.0000, 0.5050],
              ],
              [
                  [0.4950, 0.0000, 0.0000],
                  [0.0000, 1.0000, 0.0000],
                  [0.5050, 0.0000, 1.0000],
              ],
          ],
          device=device,
          dtype=torch.float32,
      )
  
      self.assertClose(clipped_faces.face_verts, clipped_face_verts)
      self.assertEqual(clipped_faces.mesh_to_face_first_idx.item(), 0)
      self.assertEqual(
          clipped_faces.num_faces_per_mesh.item(), 2
      )  # now two faces instead of 1
      self.assertClose(
          clipped_faces.faces_clipped_to_unclipped_idx,
          torch.tensor([0, 0], device=device, dtype=torch.int64),
      )
      # Neighboring face for each of the sub triangles e.g. for t1, neighbor is t2,
      # and for t2, neighbor is t1
      self.assertClose(
          clipped_faces.clipped_faces_neighbor_idx,
          torch.tensor([1, 0], device=device, dtype=torch.int64),
      )
      # barycentric_conversion is of shape (F_clipped)
      self.assertEqual(clipped_faces.barycentric_conversion.shape[0], 2)
      self.assertClose(
          clipped_faces.barycentric_conversion, barycentric_conversion
      )
      # Index into barycentric_conversion for each clipped face.
      self.assertClose(
          clipped_faces.faces_clipped_to_conversion_idx,
          torch.tensor([0, 1], device=device, dtype=torch.int64),
      )
  
imports: import unittest
  import imageio
  import numpy
  import torch
  from pytorch3d.io import save_obj
  from pytorch3d.renderer.cameras import FoVPerspectiveCameras, look_at_view_transform, PerspectiveCameras
  from pytorch3d.renderer.lighting import PointLights
  from pytorch3d.renderer.mesh import clip_faces, ClipFrustum, convert_clipped_rasterization_to_original_faces, TexturesUV
  from pytorch3d.renderer.mesh.rasterize_meshes import _RasterizeFaceVerts
  from pytorch3d.renderer.mesh.rasterizer import MeshRasterizer, RasterizationSettings
  from pytorch3d.renderer.mesh.renderer import MeshRenderer
  from pytorch3d.renderer.mesh.shader import SoftPhongShader
  from pytorch3d.renderer.mesh.textures import TexturesVertex
  from pytorch3d.structures.meshes import Meshes
  from pytorch3d.utils import torus
  from .common_testing import get_tests_dir, load_rgb_image, TestCaseMixin
label_desc: Use image node_id 8 for calling the TestRenderMeshesClipping obj's underlying member method code with example usage: obj.test_case_4() without return types