Texturing API updates

Summary:
A fairly big refactor of the texturing API with some breaking changes to how textures are defined.

Main changes:
- There are now 3 types of texture classes: `TexturesUV`, `TexturesAtlas` and `TexturesVertex`. Each class:
   - has a `sample_textures` function which accepts the `fragments` from rasterization and returns `texels`. This means that the shaders will not need to know the type of the mesh texture which will resolve several issues people were reporting on GitHub.
  -  has a `join_batch` method for joining multiple textures of the same type into a batch

Reviewed By: gkioxari

Differential Revision: D21067427

fbshipit-source-id: 4b346500a60181e72fdd1b0dd89b5505c7a33926

pytorch3d/io/obj_io.py

@@ -11,7 +11,8 @@ import numpy as np
 import torch
 from pytorch3d.io.mtl_io import load_mtl, make_mesh_texture_atlas
 from pytorch3d.io.utils import _open_file
-from pytorch3d.structures import Meshes, Textures, join_meshes_as_batch
+from pytorch3d.renderer import TexturesAtlas, TexturesUV
+from pytorch3d.structures import Meshes, join_meshes_as_batch
 
 
 def _make_tensor(data, cols: int, dtype: torch.dtype, device="cpu") -> torch.Tensor:
@@ -41,6 +42,10 @@ def _format_faces_indices(faces_indices, max_index, device, pad_value=None):
     Args:
         faces_indices: List of ints of indices.
         max_index: Max index for the face property.
+        pad_value: if any of the face_indices are padded, specify
+            the value of the padding (e.g. -1). This is only used
+            for texture indices indices where there might
+            not be texture information for all the faces.
 
     Returns:
         faces_indices: List of ints of indices.
@@ -65,7 +70,9 @@ def _format_faces_indices(faces_indices, max_index, device, pad_value=None):
         faces_indices[mask] = pad_value
 
     # Check indices are valid.
-    if torch.any(faces_indices >= max_index) or torch.any(faces_indices < 0):
+    if torch.any(faces_indices >= max_index) or (
+        pad_value is None and torch.any(faces_indices < 0)
+    ):
         warnings.warn("Faces have invalid indices")
 
     return faces_indices
@@ -227,7 +234,14 @@ def load_obj(
         )
 
 
-def load_objs_as_meshes(files: list, device=None, load_textures: bool = True):
+def load_objs_as_meshes(
+    files: list,
+    device=None,
+    load_textures: bool = True,
+    create_texture_atlas: bool = False,
+    texture_atlas_size: int = 4,
+    texture_wrap: Optional[str] = "repeat",
+):
     """
     Load meshes from a list of .obj files using the load_obj function, and
     return them as a Meshes object. This only works for meshes which have a
@@ -246,18 +260,31 @@ def load_objs_as_meshes(files: list, device=None, load_textures: bool = True):
     """
     mesh_list = []
     for f_obj in files:
-        # TODO: update this function to support the two texturing options.
-        verts, faces, aux = load_obj(f_obj, load_textures=load_textures)
-        verts = verts.to(device)
+        verts, faces, aux = load_obj(
+            f_obj,
+            load_textures=load_textures,
+            create_texture_atlas=create_texture_atlas,
+            texture_atlas_size=texture_atlas_size,
+            texture_wrap=texture_wrap,
+        )
         tex = None
-        tex_maps = aux.texture_images
-        if tex_maps is not None and len(tex_maps) > 0:
-            verts_uvs = aux.verts_uvs[None, ...].to(device)  # (1, V, 2)
-            faces_uvs = faces.textures_idx[None, ...].to(device)  # (1, F, 3)
-            image = list(tex_maps.values())[0].to(device)[None]
-            tex = Textures(verts_uvs=verts_uvs, faces_uvs=faces_uvs, maps=image)
+        if create_texture_atlas:
+            # TexturesAtlas type
+            tex = TexturesAtlas(atlas=[aux.texture_atlas])
+        else:
+            # TexturesUV type
+            tex_maps = aux.texture_images
+            if tex_maps is not None and len(tex_maps) > 0:
+                verts_uvs = aux.verts_uvs.to(device)  # (V, 2)
+                faces_uvs = faces.textures_idx.to(device)  # (F, 3)
+                image = list(tex_maps.values())[0].to(device)[None]
+                tex = TexturesUV(
+                    verts_uvs=[verts_uvs], faces_uvs=[faces_uvs], maps=image
+                )
 
-        mesh = Meshes(verts=[verts], faces=[faces.verts_idx.to(device)], textures=tex)
+        mesh = Meshes(
+            verts=[verts.to(device)], faces=[faces.verts_idx.to(device)], textures=tex
+        )
         mesh_list.append(mesh)
     if len(mesh_list) == 1:
         return mesh_list[0]