IO: Reversed persistent ID order in exports to Alembic and USD

Each duplicated (a.k.a. instanced) object has a Persistent ID, which
identifies a dupli within the context of its duplicator. This ID
consists of several numbers when there are nested duplis (for example a
mesh instancing empties on its vertices, where each empty instances a
collection). When exporting to Alembic/USD, these are used to uniquely
name the duplicated objects in the export.

This commit reverses the order of the persistent ID numbers, so that the
first number identifies the first level of recursion. This produces
trees like this:

    ABC
     `--Triangle
         |--Triangle
         |--Empty-1
         |    `--Pole-1-0
         |        |--Pole
         |        `--Block-1-1
         |            `--Block
         |--Empty
         |    `--Pole-0
         |        |--Pole
         |        `--Block-1
         |            `--Block
         |--Empty-2
         |    `--Pole-2-0
         |        |--Pole
         |        `--Block-2-1
         |            `--Block
         `--Empty-0
             `--Pole-0-0
                 |--Pole
                 `--Block-0-1
                     `--Block

It is now clearer that `Pole-2-0` and `Block-2-1` are instanced by
`Empty-2`. Before this commit, they would have been named `Pole-0-2` and
`Block-1-2`.

2 files changed, 45 insertions, 12 deletions

diff --git a/tests/gtests/usd/object_identifier_test.cc b/tests/gtests/usd/object_identifier_test.cc
index a914ec7e89d..810d4470260 100644
--- a/tests/gtests/usd/object_identifier_test.cc
+++ b/tests/gtests/usd/object_identifier_test.cc
@@ -39,11 +39,30 @@ Object *fake_pointer(int value)
 /* PersistentID subclass for use in tests, making it easier to construct test values. */
 class TestPersistentID : public PersistentID {
  public:
-  TestPersistentID(int value0, int value1)
+  TestPersistentID(int value0,
+                   int value1,
+                   int value2,
+                   int value3,
+                   int value4,
+                   int value5,
+                   int value6,
+                   int value7)
   {
     persistent_id_[0] = value0;
     persistent_id_[1] = value1;
-    persistent_id_[2] = INT_MAX;
+    persistent_id_[2] = value2;
+    persistent_id_[3] = value3;
+    persistent_id_[4] = value4;
+    persistent_id_[5] = value5;
+    persistent_id_[6] = value6;
+    persistent_id_[7] = value7;
+  }
+  TestPersistentID(int value0, int value1, int value2)
+      : TestPersistentID(value0, value1, value2, INT_MAX, INT_MAX, INT_MAX, INT_MAX, INT_MAX)
+  {
+  }
+  TestPersistentID(int value0, int value1) : TestPersistentID(value0, value1, INT_MAX)
+  {
   }
   explicit TestPersistentID(int value0) : TestPersistentID(value0, INT_MAX)
   {
@@ -199,5 +218,19 @@ TEST_F(PersistentIDTest, instancer_id)
   EXPECT_LT(expect_instancer_id, empty_id);
 }
 
+TEST_F(PersistentIDTest, as_object_name_suffix)
+{
+  EXPECT_EQ("", PersistentID().as_object_name_suffix());
+  EXPECT_EQ("47", TestPersistentID(47).as_object_name_suffix());
+  EXPECT_EQ("327-47", TestPersistentID(47, 327).as_object_name_suffix());
+  EXPECT_EQ("42-327-47", TestPersistentID(47, 327, 42).as_object_name_suffix());
+
+  EXPECT_EQ("7-6-5-4-3-2-1-0", TestPersistentID(0, 1, 2, 3, 4, 5, 6, 7).as_object_name_suffix());
+
+  EXPECT_EQ("0-0-0", TestPersistentID(0, 0, 0).as_object_name_suffix());
+  EXPECT_EQ("0-0", TestPersistentID(0, 0).as_object_name_suffix());
+  EXPECT_EQ("-3--2--1", TestPersistentID(-1, -2, -3).as_object_name_suffix());
+}
+
 }  // namespace io
 }  // namespace blender
diff --git a/tests/python/alembic_tests.py b/tests/python/alembic_tests.py
index 4d7ae97b327..66545dc85c7 100644
--- a/tests/python/alembic_tests.py
+++ b/tests/python/alembic_tests.py
@@ -254,7 +254,7 @@ class DupliGroupExportTest(AbstractAlembicTest):
         #  `--Triangle
         #      |--Triangle
         #      |--Empty-1
-        #      |    `--Pole-0-1
+        #      |    `--Pole-1-0
         #      |        |--Pole
         #      |        `--Block-1-1
         #      |            `--Block
@@ -264,18 +264,18 @@ class DupliGroupExportTest(AbstractAlembicTest):
         #      |        `--Block-1
         #      |            `--Block
         #      |--Empty-2
-        #      |    `--Pole-0-2
+        #      |    `--Pole-2-0
         #      |        |--Pole
-        #      |        `--Block-1-2
+        #      |        `--Block-2-1
         #      |            `--Block
         #      `--Empty-0
         #          `--Pole-0-0
         #              |--Pole
-        #              `--Block-1-0
+        #              `--Block-0-1
         #                  `--Block
 
         # Now check the resulting Alembic file.
-        xform = self.abcprop(abc, '/Triangle/Empty-1/Pole-0-1/Block-1-1/.xform')
+        xform = self.abcprop(abc, '/Triangle/Empty-1/Pole-1-0/Block-1-1/.xform')
         self.assertEqual(1, xform['.inherits'])
         self.assertAlmostEqualFloatArray(
             xform['.vals'],
@@ -288,17 +288,17 @@ class DupliGroupExportTest(AbstractAlembicTest):
         # If the property can be gotten, the hierarchy is okay. No need to actually check each xform.
         self.abcprop(abc, '/Triangle/.xform')
         self.abcprop(abc, '/Triangle/Empty-1/.xform')
-        self.abcprop(abc, '/Triangle/Empty-1/Pole-0-1/.xform')
-        self.abcprop(abc, '/Triangle/Empty-1/Pole-0-1/Block-1-1/.xform')
+        self.abcprop(abc, '/Triangle/Empty-1/Pole-1-0/.xform')
+        self.abcprop(abc, '/Triangle/Empty-1/Pole-1-0/Block-1-1/.xform')
         self.abcprop(abc, '/Triangle/Empty/.xform')
         self.abcprop(abc, '/Triangle/Empty/Pole-0/.xform')
         self.abcprop(abc, '/Triangle/Empty/Pole-0/Block-1/.xform')
         self.abcprop(abc, '/Triangle/Empty-2/.xform')
-        self.abcprop(abc, '/Triangle/Empty-2/Pole-0-2/.xform')
-        self.abcprop(abc, '/Triangle/Empty-2/Pole-0-2/Block-1-2/.xform')
+        self.abcprop(abc, '/Triangle/Empty-2/Pole-2-0/.xform')
+        self.abcprop(abc, '/Triangle/Empty-2/Pole-2-0/Block-2-1/.xform')
         self.abcprop(abc, '/Triangle/Empty-0/.xform')
         self.abcprop(abc, '/Triangle/Empty-0/Pole-0-0/.xform')
-        self.abcprop(abc, '/Triangle/Empty-0/Pole-0-0/Block-1-0/.xform')
+        self.abcprop(abc, '/Triangle/Empty-0/Pole-0-0/Block-0-1/.xform')
 
 
 class CurveExportTest(AbstractAlembicTest):