Tutorials textures updates and fix bug in extending meshes with uv textures

Summary:
Found a bug in extending textures with vertex uv coordinates. This was due to the padded -> list conversion of vertex uv coordinates i.e.                 The number of vertices in the mesh and in verts_uvs can differ
e.g. if a vertex is shared between 3 faces, it can
have up to 3 different uv coordinates. Therefore we cannot convert directly from padded to list using _num_verts_per_mesh

Reviewed By: bottler

Differential Revision: D23233595

fbshipit-source-id: 0c66d15baae697ead0bdc384f74c27d4c6539fc9

docs/tutorials/render_textured_meshes.ipynb

@@ -87,7 +87,7 @@
     "from pytorch3d.io import load_objs_as_meshes, load_obj\n",
     "\n",
     "# Data structures and functions for rendering\n",
-    "from pytorch3d.structures import Meshes, Textures\n",
+    "from pytorch3d.structures import Meshes\n",
     "from pytorch3d.renderer import (\n",
     "    look_at_view_transform,\n",
     "    FoVPerspectiveCameras, \n",
@@ -97,7 +97,8 @@
     "    RasterizationSettings, \n",
     "    MeshRenderer, \n",
     "    MeshRasterizer,  \n",
-    "    SoftPhongShader\n",
+    "    SoftPhongShader,\n",
+    "    TexturesUV\n",
     ")\n",
     "\n",
     "# add path for demo utils functions \n",
@@ -170,7 +171,7 @@
     "\n",
     "**Meshes** is a unique datastructure provided in PyTorch3D for working with batches of meshes of different sizes. \n",
     "\n",
-    "**Textures** is an auxillary datastructure for storing texture information about meshes. \n",
+    "**TexturesUV** is an auxillary datastructure for storing vertex uv and texture maps for meshes. \n",
     "\n",
     "**Meshes** has several class methods which are used throughout the rendering pipeline."
    ]
@@ -537,7 +538,7 @@
    "source": [
     "# We can pass arbirary keyword arguments to the rasterizer/shader via the renderer\n",
     "# so the renderer does not need to be reinitialized if any of the settings change.\n",
-    "images = renderer(meshes, cameras=cameras, lights=lights)"
+    "images = renderer(mesh, cameras=cameras, lights=lights)"
    ]
   },
   {
@@ -582,9 +583,9 @@
    "backup_notebook_id": "569222367081034"
   },
   "kernelspec": {
-   "display_name": "pytorch3d (local)",
+   "display_name": "intro_to_cv",
    "language": "python",
-   "name": "pytorch3d_local"
+   "name": "bento_kernel_intro_to_cv"
   },
   "language_info": {
    "codemirror_mode": {