When building with USD enabled, add functionality that automatically registers the mujoco USD plugins.

PiperOrigin-RevId: 846767370
Change-Id: Ieedbe127353623c11150551c1409d340dbc57421

src/experimental/usd/utils.cc

@@ -12,8 +12,17 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#include <mujoco/experimental/usd/utils.h>
+#include <cstddef>
+#include <string>
 
+#if defined(_WIN32) || defined(__CYGWIN__)
+#include <windows.h>
+#else
+#include <dlfcn.h>
+#endif
+#include <pxr/base/plug/registry.h>
+
+#include <mujoco/experimental/usd/utils.h>
 #include <mujoco/mujoco.h>
 #include <pxr/usd/sdf/path.h>
 
@@ -42,3 +51,56 @@ pxr::SdfPath GetUsdPrimPathUserValue(mjsElement* element) {
 
 }  // namespace usd
 }  // namespace mujoco
+
+namespace {
+//Automatically register USD plugins when the library is loaded.
+//This avoids the need for users to manually set PXR_PLUGINPATH_NAME.
+[[maybe_unused]]
+bool RegisterMujocoUsdPlugins() {
+  std::string plugin_path;
+
+#if defined(_WIN32) || defined(__CYGWIN__)
+  HMODULE hModule = NULL;
+  if (GetModuleHandleEx(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS |
+                            GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT,
+                        (LPCTSTR)&mujoco::usd::SetUsdPrimPathUserValue,
+                        &hModule)) {
+    char path[MAX_PATH];
+    if (GetModuleFileName(hModule, path, MAX_PATH)) {
+      std::string lib_path(path);
+      // Remove filename to get directory
+      size_t last_slash = lib_path.find_last_of("\\/");
+      if (last_slash != std::string::npos) {
+        plugin_path = lib_path.substr(0, last_slash);
+      }
+    }
+  }
+#else
+  Dl_info info;
+  if (dladdr((void*)&mujoco::usd::SetUsdPrimPathUserValue, &info)) {
+    std::string lib_path(info.dli_fname);
+    // Remove filename to get directory
+    size_t last_slash = lib_path.find_last_of('/');
+    if (last_slash != std::string::npos) {
+      plugin_path = lib_path.substr(0, last_slash);
+    }
+  }
+#endif
+
+  if (!plugin_path.empty()) {
+#if defined(_WIN32) || defined(__CYGWIN__)
+    std::string full_path =
+        plugin_path + "\\" + "mujoco-usd-resources" + "\\**\\plugInfo.json";
+#else
+    std::string full_path =
+        plugin_path + "/" + "mujoco-usd-resources" + "/**/plugInfo.json";
+#endif
+    pxr::PlugRegistry::GetInstance().RegisterPlugins(full_path);
+  }
+  return true;
+}
+
+// Force registration at library load time.
+bool registered = RegisterMujocoUsdPlugins();
+
+}  // namespace