USD: add USD importer

This is an initial implementation of a USD importer.

This work is comprised of Tangent Animation's open source USD importer,
combined with features @makowalski had implemented.

The design is very similar to the approach taken in the Alembic
importer. The core functionality resides in a collection of "reader"
classes, each of which is responsible for converting an instance of a
USD prim to the corresponding Blender Object representation.

The flow of control for the conversion can be followed in the
`import_startjob()` and `import_endjob()` functions in `usd_capi.cc`.
The `USDStageReader` class is responsible for traversing the USD stage
and instantiating the appropriate readers.

Reviewed By: sybren, HooglyBoogly

Differential Revision: https://developer.blender.org/D10700

1 files changed, 43 insertions, 0 deletions

diff --git a/source/blender/io/usd/intern/usd_common.cc b/source/blender/io/usd/intern/usd_common.cc
new file mode 100644
index 00000000000..0cd9c3019ef
--- /dev/null
+++ b/source/blender/io/usd/intern/usd_common.cc
@@ -0,0 +1,43 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * The Original Code is Copyright (C) 2021 Blender Foundation.
+ * All rights reserved.
+ */
+
+#include "usd_common.h"
+
+#include <pxr/base/plug/registry.h>
+
+#include "BKE_appdir.h"
+
+namespace blender::io::usd {
+
+void ensure_usd_plugin_path_registered()
+{
+  static bool plugin_path_registered = false;
+  if (plugin_path_registered) {
+    return;
+  }
+  plugin_path_registered = true;
+
+  /* Tell USD which directory to search for its JSON files. If 'datafiles/usd'
+   * does not exist, the USD library will not be able to read or write any files. */
+  const std::string blender_usd_datafiles = BKE_appdir_folder_id(BLENDER_DATAFILES, "usd");
+  /* The trailing slash indicates to the USD library that the path is a directory. */
+  pxr::PlugRegistry::GetInstance().RegisterPlugins(blender_usd_datafiles + "/");
+}
+
+}  // namespace blender::io::usd