Add separate build step for OpenUSD to third_party_deps.

This will fetch and call the build_usd.py build helper for OpenUSD and build within the MuJoCo _deps folder. Simplifying the build process for MuJoCo with USD. Users can still provide their own USD build, but must now do so via pxr_DIR.

PiperOrigin-RevId: 846735578
Change-Id: I0da7eb2da6465e2d518084340e762bf370adb6d5

cmake/third_party_deps/openusd.cmake

@@ -0,0 +1,38 @@
+# Copyright 2025 DeepMind Technologies Limited
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Find OpenUSD package. The user can either provide pxr_DIR to use their own
+# OpenUSD installation or they can build external_dependencies.
+#
+# We use QUIET here to provide a better error message when pxr is not found.
+find_package(pxr
+  QUIET
+  HINTS "${CMAKE_BINARY_DIR}/_deps/openusd-build"
+)
+
+if(NOT pxr_FOUND)
+    message(FATAL_ERROR
+        "-----------------------------------------------------------\n"
+        "USD Configuration Error:\n${pxr_NOT_FOUND_MESSAGE}\n"
+        "If you have built USD yourself, provide -Dpxr_DIR=your_pxr_install_dir' \n"
+        "Otherwise you can build cmake/third_party_deps/openusd:\n"
+        "cd ~/mujoco\n"
+        "cmake -Bcmake/third_party_deps/openusd/build cmake/third_party_deps/openusd -DBUILD_USD=True\n"
+        "cmake --build cmake/third_party_deps/openusd/build\n"
+        "cmake -Bbuild -S. -DMUJOCO_WITH_USD=True\n"
+        "cmake --build build\n"
+        "cmake --install build"
+        "-----------------------------------------------------------"
+    )
+endif()