Rendering texturing fixes

Summary:
Fix errors raised by issue on GitHub - extending mesh textures + rendering with Gourad and Phong shaders.

https://github.com/facebookresearch/pytorch3d/issues/97

Reviewed By: gkioxari

Differential Revision: D20319610

fbshipit-source-id: d1c692ff0b9397a77a9b829c5c731790de70c09f

tests/test_rendering_utils.py

@@ -1,6 +1,7 @@
 # Copyright (c) Facebook, Inc. and its affiliates. All rights reserved.
 
 
+import numpy as np
 import unittest
 import torch
 
@@ -61,3 +62,28 @@ class TestTensorProperties(TestCaseMixin, unittest.TestCase):
         example = TensorPropertiesTestClass(x=(), y=())
         self.assertTrue(len(example) == 0)
         self.assertTrue(example.isempty())
+
+    def test_gather_props(self):
+        N = 4
+        x = torch.randn((N, 3, 4))
+        y = torch.randn((N, 5))
+        test_class = TensorPropertiesTestClass(x=x, y=y)
+
+        S = 15
+        idx = torch.tensor(np.random.choice(N, S))
+        test_class_gathered = test_class.gather_props(idx)
+
+        self.assertTrue(test_class_gathered.x.shape == (S, 3, 4))
+        self.assertTrue(test_class_gathered.y.shape == (S, 5))
+
+        for i in range(N):
+            inds = idx == i
+            if inds.sum() > 0:
+                # Check the gathered points in the output have the same value from
+                # the input.
+                self.assertClose(
+                    test_class_gathered.x[inds].mean(dim=0), x[i, ...]
+                )
+                self.assertClose(
+                    test_class_gathered.y[inds].mean(dim=0), y[i, ...]
+                )