fix _num_faces_per_mesh in join_batch

Summary: As reported in https://github.com/facebookresearch/pytorch3d/pull/1100, _num_faces_per_mesh was changing in the source mesh in join_batch. This affects both TexturesUV and TexturesAtlas

Reviewed By: nikhilaravi

Differential Revision: D34643675

fbshipit-source-id: d67bdaca7278f18a76cfb15ba59d0ea85575bd36

pytorch3d/renderer/mesh/textures.py

@@ -569,7 +569,7 @@ class TexturesAtlas(TexturesBase):
 
         atlas_list = []
         atlas_list += self.atlas_list()
-        num_faces_per_mesh = self._num_faces_per_mesh
+        num_faces_per_mesh = self._num_faces_per_mesh.copy()
         for tex in textures:
             atlas_list += tex.atlas_list()
             num_faces_per_mesh += tex._num_faces_per_mesh
@@ -1073,7 +1073,7 @@ class TexturesUV(TexturesBase):
         faces_uvs_list += self.faces_uvs_list()
         verts_uvs_list += self.verts_uvs_list()
         maps_list += self.maps_list()
-        num_faces_per_mesh = self._num_faces_per_mesh
+        num_faces_per_mesh = self._num_faces_per_mesh.copy()
         for tex in textures:
             verts_uvs_list += tex.verts_uvs_list()
             faces_uvs_list += tex.faces_uvs_list()

tests/test_render_meshes.py

@@ -793,7 +793,12 @@ class TestRenderMeshes(TestCaseMixin, unittest.TestCase):
             faces_uvs=torch.arange(150).reshape(1, 50, 3),
             verts_uvs=torch.rand(1, 150, 2) * 0.2 + 0.3,
         )
+        self.assertEqual(a._num_faces_per_mesh, [100])
+        self.assertEqual(b._num_faces_per_mesh, [50])
         c = a.join_batch([b]).join_scene()
+        self.assertEqual(a._num_faces_per_mesh, [100])
+        self.assertEqual(b._num_faces_per_mesh, [50])
+        self.assertEqual(c._num_faces_per_mesh, [150])
 
         color = c.faces_verts_textures_packed()
         color1 = color[:100, :, 0].flatten()
@@ -904,7 +909,12 @@ class TestRenderMeshes(TestCaseMixin, unittest.TestCase):
         textures2 = TexturesAtlas(atlas=[atlas2])
         mesh1 = Meshes(verts=[verts], faces=[faces], textures=textures1)
         mesh2 = Meshes(verts=[verts_shifted1], faces=[faces], textures=textures2)
+        self.assertEqual(textures1._num_faces_per_mesh, [len(faces)])
+        self.assertEqual(textures2._num_faces_per_mesh, [len(faces)])
         mesh_joined = join_meshes_as_scene([mesh1, mesh2])
+        self.assertEqual(textures1._num_faces_per_mesh, [len(faces)])
+        self.assertEqual(textures2._num_faces_per_mesh, [len(faces)])
+        self.assertEqual(mesh_joined.textures._num_faces_per_mesh, [len(faces) * 2])
 
         R, T = look_at_view_transform(18, 0, 0)
         cameras = FoVPerspectiveCameras(device=device, R=R, T=T)