USD: remove library initialisation hack

Remove the hack for library initialisation; this is no longer necessary
as the required information can be passed to the USD library after its
static initialisers have run.

This new approach is compatible with both the patched and original USD
library. This means that platform maintainers don't need to rebuild the
USD library until the next upgrade.

Manifest Task: https://developer.blender.org/T80320

2 files changed, 17 insertions, 22 deletions

diff --git a/source/blender/io/usd/intern/usd_capi.cc b/source/blender/io/usd/intern/usd_capi.cc
index b5b314136ed..52075728e3e 100644
--- a/source/blender/io/usd/intern/usd_capi.cc
+++ b/source/blender/io/usd/intern/usd_capi.cc
@@ -20,6 +20,7 @@
 #include "usd.h"
 #include "usd_hierarchy_iterator.h"
 
+#include <pxr/base/plug/registry.h>
 #include <pxr/pxr.h>
 #include <pxr/usd/usd/stage.h>
 #include <pxr/usd/usdGeom/tokens.h>
@@ -45,17 +46,6 @@
 #include "WM_api.h"
 #include "WM_types.h"
 
-/* Workaround to make it possible to pass a path at runtime to USD.
- *
- * USD requires some JSON files, and it uses a static constructor to determine the possible
- * file-system paths to find those files. This made it impossible for Blender to pass a path to
- * the USD library at runtime, as the constructor would run before Blender's main() function.
- * We have patched USD (see usd.diff) to avoid that particular static constructor, and have an
- * initialization function instead.
- *
- * This function is implemented in the USD source code, `pxr/base/plug/initConfig.cpp`. */
-extern "C" void usd_initialise_plugin_path(const char *datafiles_usd_path);
-
 namespace blender {
 namespace io {
 namespace usd {
@@ -81,7 +71,9 @@ static void ensure_usd_plugin_path_registered(void)
 
   /* 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. */
-  usd_initialise_plugin_path(BKE_appdir_folder_id(BLENDER_DATAFILES, "usd"));
+  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 + "/");
 }
 
 static void export_startjob(void *customdata,
diff --git a/source/blender/io/usd/tests/usd_stage_creation_test.cc b/source/blender/io/usd/tests/usd_stage_creation_test.cc
index e6bd0bab6ce..3d28d8f8f5a 100644
--- a/source/blender/io/usd/tests/usd_stage_creation_test.cc
+++ b/source/blender/io/usd/tests/usd_stage_creation_test.cc
@@ -17,6 +17,8 @@
  * All rights reserved.
  */
 #include "testing/testing.h"
+
+#include <pxr/base/plug/registry.h>
 #include <pxr/usd/usd/stage.h>
 
 #include <string>
@@ -26,11 +28,6 @@
 
 #include "BKE_appdir.h"
 
-extern "C" {
-/* Workaround to make it possible to pass a path at runtime to USD. See creator.c. */
-void usd_initialise_plugin_path(const char *datafiles_usd_path);
-}
-
 namespace blender::io::usd {
 
 class USDStageCreationTest : public testing::Test {
@@ -44,9 +41,16 @@ TEST_F(USDStageCreationTest, JSONFileLoadingTest)
   }
 
   char usd_datafiles_dir[FILE_MAX];
-  BLI_path_join(usd_datafiles_dir, FILE_MAX, release_dir.c_str(), "datafiles", "usd", nullptr);
+  const size_t path_len = BLI_path_join(
+      usd_datafiles_dir, FILE_MAX, release_dir.c_str(), "datafiles", "usd", nullptr);
+
+  /* BLI_path_join removes trailing slashes, but the USD library requires one in order to recognise
+   * the path as directory. */
+  BLI_assert(path_len + 1 < FILE_MAX);
+  usd_datafiles_dir[path_len] = '/';
+  usd_datafiles_dir[path_len + 1] = '\0';
 
-  usd_initialise_plugin_path(usd_datafiles_dir);
+  pxr::PlugRegistry::GetInstance().RegisterPlugins(usd_datafiles_dir);
 
   /* Simply the ability to create a USD Stage for a specific filename means that the extension
    * has been recognized by the USD library, and that a USD plugin has been loaded to write such
@@ -61,9 +65,8 @@ TEST_F(USDStageCreationTest, JSONFileLoadingTest)
     unlink(filename.c_str());
   }
   else {
-    FAIL() << "unable to find suitable USD plugin to write " << filename
-           << "; re-run with the environment variable PXR_PATH_DEBUG non-empty to see which paths "
-              "are considered.";
+    FAIL() << "unable to find suitable USD plugin to write " << filename << "; looked in "
+           << usd_datafiles_dir;
   }
 }