FetchContent mujoco 3.0.1 if MUJOCO_ROOT_DIR not provided

CMakeLists.txt

@@ -14,7 +14,20 @@ project(
   VERSION 1.0.0)
 
 if(NOT DEFINED MUJOCO_ROOT_DIR)
-  message(FATAL_ERROR "Provide MUJOCO_ROOT_DIR")
+  # FetchContent from CMake >= 3.11
+  if(${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.11")
+    set(MUJOCO_DOWNLOAD_DIR "$ENV{HOME}/.mujoco/mujoco301")
+    message(STATUS "MUJOCO_ROOT_DIR is not provided. Will be automatically downloaded to ${MUJOCO_DOWNLOAD_DIR}.")
+    include(FetchContent)
+    FetchContent_Declare(mujoco
+      URL https://github.com/google-deepmind/mujoco/releases/download/3.0.1/mujoco-3.0.1-linux-x86_64.tar.gz
+      SOURCE_DIR ${MUJOCO_DOWNLOAD_DIR}
+      )
+    FetchContent_MakeAvailable(mujoco)
+    set(MUJOCO_ROOT_DIR "${MUJOCO_DOWNLOAD_DIR}")
+  else()
+    message(FATAL_ERROR "MUJOCO_ROOT_DIR is not provided. Download MuJoCo from mujoco.org and provide MUJOCO_ROOT_DIR.")
+  endif()
 endif()
 
 find_package(mc_rtc REQUIRED)