Submeshing TexturesAtlas for PyTorch3D 3D Rendering

Summary: Implement submeshing for TexturesAtlas and add associated test

Reviewed By: bottler

Differential Revision: D52334053

fbshipit-source-id: d54080e9af1f0c01551702736e858e3bd439ac58

Author: ttanpcs

pytorch3d/renderer/mesh/textures.py

@@ -549,6 +549,33 @@ def sample_textures(self, fragments, **kwargs) -> torch.Tensor:
 
         return texels
 
+    def submeshes(
+        self,
+        vertex_ids_list: List[List[torch.LongTensor]],
+        faces_ids_list: List[List[torch.LongTensor]],
+    ) -> "TexturesAtlas":
+        """
+        Extract a sub-texture for use in a submesh.
+
+        If the meshes batch corresponding to this TextureAtlas contains
+        `n = len(faces_ids_list)` meshes, then self.atlas_list()
+        will be of length n. After submeshing, we obtain a batch of
+        `k = sum(len(v) for v in atlas_list` submeshes (see Meshes.submeshes). This
+        function creates a corresponding TexturesAtlas object with `atlas_list`
+        of length `k`.
+        """
+        if len(faces_ids_list) != len(self.atlas_list()):
+            raise IndexError(
+                "faces_ids_list must be of " "the same length as atlas_list."
+            )
+
+        sub_features = []
+        for atlas, faces_ids in zip(self.atlas_list(), faces_ids_list):
+            for faces_ids_submesh in faces_ids:
+                sub_features.append(atlas[faces_ids_submesh])
+
+        return self.__class__(sub_features)
+
     def faces_verts_textures_packed(self) -> torch.Tensor:
         """
         Samples texture from each vertex for each face in the mesh.

pytorch3d/structures/meshes.py

@@ -1576,8 +1576,6 @@ def submeshes(
         Returns:
           Meshes object of length `sum(len(ids) for ids in face_indices)`.
 
-        Submeshing only works with no textures, TexturesVertex, or TexturesUV.
-
         Example 1:
 
         If `meshes` has batch size 1, and `face_indices` is a 1D LongTensor,

tests/test_texturing.py

@@ -576,6 +576,39 @@ def test_sample_textures_error(self):
         with self.assertRaisesRegex(ValueError, "do not match the dimensions"):
             meshes.sample_textures(None)
 
+    def test_submeshes(self):
+        N = 2
+        V = 5
+        F = 5
+        tex = TexturesAtlas(
+            atlas=torch.arange(N * F * 4 * 4 * 3, dtype=torch.float32).reshape(
+                N, F, 4, 4, 3
+            )
+        )
+
+        verts = torch.rand(size=(N, V, 3))
+        faces = torch.randint(size=(N, F, 3), high=V)
+        mesh = Meshes(verts=verts, faces=faces, textures=tex)
+
+        sub_faces = [
+            [torch.tensor([0, 2]), torch.tensor([1, 2])],
+            [],
+        ]
+        subtex = mesh.submeshes(sub_faces).textures
+        subtex_faces = subtex.atlas_list()
+
+        self.assertEqual(len(subtex_faces), 2)
+        self.assertClose(
+            subtex_faces[0].flatten().msort(),
+            torch.cat(
+                (
+                    torch.arange(4 * 4 * 3, dtype=torch.float32),
+                    torch.arange(96, 96 + 4 * 4 * 3, dtype=torch.float32),
+                ),
+                0,
+            ),
+        )
+
 
 class TestTexturesUV(TestCaseMixin, unittest.TestCase):
     def setUp(self) -> None: