Replace OpenGL dependency CMake variables with targets

CHANGELOG.md

@@ -95,6 +95,7 @@
   * Added CI for multiple Linux platforms: arm64 and ppc64le: [#1531](https://github.com/dartsim/dart/pull/1531)
   * Fixed Aspect/Composite-relate tests on Windows/MSVC: [#1541](https://github.com/dartsim/dart/pull/1541), [#1542](https://github.com/dartsim/dart/pull/1542)
   * Added `DART_SKIP_<dep>`_advanced option: [#1529](https://github.com/dartsim/dart/pull/1529)
+  * Replaced OpenGL dependency variables with targets: [#1552](https://github.com/dartsim/dart/pull/1552)
 
 * Documentation
 

cmake/DARTFindOpenGL.cmake

@@ -14,7 +14,12 @@ if(POLICY CMP0072)
   cmake_policy(SET CMP0072 OLD)
 endif()
 
-find_package(OpenGL QUIET MODULE)
+# Use OpenGL config if available
+find_package(OpenGL QUIET CONFIG)
+# Otherwise, fall back to FindOpenGL.cmake provided by CMake
+if(NOT OPENGL_FOUND)
+  find_package(OpenGL QUIET MODULE)
+endif()
 
 cmake_policy(POP)
 

cmake/DARTFindOpenSceneGraph.cmake

@@ -0,0 +1,63 @@
+# Copyright (c) 2011-2021, The DART development contributors
+# All rights reserved.
+#
+# The list of contributors can be found at:
+#   https://github.com/dartsim/dart/blob/master/LICENSE
+#
+# This file is provided under the "BSD-style" License
+
+if (CMAKE_VERSION VERSION_LESS 3.12)
+  get_property(old_find_library_use_lib64_paths GLOBAL PROPERTY FIND_LIBRARY_USE_LIB64_PATHS)
+  set_property(GLOBAL PROPERTY FIND_LIBRARY_USE_LIB64_PATHS TRUE)
+endif()
+
+find_package(OpenSceneGraph 3.0 QUIET
+  COMPONENTS osg osgViewer osgManipulator osgGA osgDB osgShadow
+)
+
+if (CMAKE_VERSION VERSION_LESS 3.12)
+  set_property(GLOBAL PROPERTY FIND_LIBRARY_USE_LIB64_PATHS ${old_find_library_use_lib64_paths})
+endif()
+
+# It seems that OPENSCENEGRAPH_FOUND will inadvertently get set to true when
+# OpenThreads is found, even if OpenSceneGraph is not installed. This is quite
+# possibly a bug in OSG's cmake configuration file. For now, it seems that
+# requiring OSG_FOUND to be true as well fixes this.
+if(OPENSCENEGRAPH_FOUND AND OSG_FOUND)
+  if(DART_VERBOSE)
+    message(STATUS "Looking for OpenSceneGraph - ${OPENSCENEGRAPH_VERSION} found")
+  endif()
+else()
+  # dart-gui-osg requires both OSG and OpenThreads. This section attempts to
+  # identify which of those are missing from the building machine and offer
+  # advice to the user for getting dart-gui-osg to build.
+  find_package(OpenThreads QUIET)
+  if(OPENTHREADS_FOUND)
+    set(warning_msg "Could NOT find OpenSceneGraph")
+  else()
+    if(OSG_LIBRARY)
+      set(warning_msg "Could NOT find OpenThreads")
+    else()
+      set(warning_msg "Could NOT find OpenSceneGraph nor OpenThreads")
+    endif()
+  endif()
+  message(STATUS "${warning_msg} -- we will skip dart-gui-osg\n"
+          "If you believe you do have both OSG and OpenThreads installed, try setting OSG_DIR")
+  return()
+endif()
+
+# Define an imported target "osg::osg" if it's not defined in the provided find
+# module.
+#
+# This is required to make the DART module that uses OpenSceneGraph relocatable.
+# For that, any DART targets (e.g., dart-gui-osg) should use "osg::osg" instead
+# of OPENSCENEGRAPH_INCLUDE_DIRS and OPENSCENEGRAPH_LIBRARIES because the
+# variables contain absolute paths of OpenSceneGraph that could be different in
+# where the system that DART is built and where the system that consumes DART.
+if((OPENSCENEGRAPH_FOUND OR OpenSceneGraph_FOUND) AND NOT TARGET osg::osg)
+  add_library(osg::osg INTERFACE IMPORTED)
+  set_target_properties(osg::osg PROPERTIES
+    INTERFACE_INCLUDE_DIRECTORIES "${OPENSCENEGRAPH_INCLUDE_DIRS}"
+    INTERFACE_LINK_LIBRARIES "${OPENSCENEGRAPH_LIBRARIES}"
+  )
+endif()

dart/gui/CMakeLists.txt

@@ -42,13 +42,12 @@ get_property(dart_gui_sources GLOBAL PROPERTY DART_GUI_SOURCES)
 dart_add_library(${target_name}
   ${hdrs} ${srcs} ${dart_gui_headers} ${dart_gui_sources}
 )
-target_include_directories(${target_name} PUBLIC ${GLUT_INCLUDE_DIRS})
 target_link_libraries(${target_name}
   PUBLIC
     dart-utils
-    ${GLUT_LIBRARIES}
-    OpenGL::GLU
     OpenGL::GL
+    OpenGL::GLU
+    GLUT::GLUT
     ${PROJECT_NAME}-external-lodepng
     ${PROJECT_NAME}-external-imgui
 )

dart/gui/osg/CMakeLists.txt

@@ -19,52 +19,11 @@ endif()
 
 # OpenSceneGraph
 if(DART_BUILD_GUI_OSG)
-
-  if (CMAKE_VERSION VERSION_LESS 3.12)
-    get_property(old_find_library_use_lib64_paths GLOBAL PROPERTY FIND_LIBRARY_USE_LIB64_PATHS)
-    set_property(GLOBAL PROPERTY FIND_LIBRARY_USE_LIB64_PATHS TRUE)
-  endif()
-
-  find_package(OpenSceneGraph ${min_osg_version} QUIET
-    COMPONENTS osg osgViewer osgManipulator osgGA osgDB osgShadow
-  )
-
-  if (CMAKE_VERSION VERSION_LESS 3.12)
-    set_property(GLOBAL PROPERTY FIND_LIBRARY_USE_LIB64_PATHS ${old_find_library_use_lib64_paths})
-  endif()
-
-  # It seems that OPENSCENEGRAPH_FOUND will inadvertently get set to true when
-  # OpenThreads is found, even if OpenSceneGraph is not installed. This is quite
-  # possibly a bug in OSG's cmake configuration file. For now, it seems that
-  # requiring OSG_FOUND to be true as well fixes this.
-  if(OPENSCENEGRAPH_FOUND AND OSG_FOUND)
-    if(DART_VERBOSE)
-      message(STATUS "Looking for OpenSceneGraph - ${OPENSCENEGRAPH_VERSION} found")
-    endif()
-  else()
-    # dart-gui-osg requires both OSG and OpenThreads. This section attempts to
-    # identify which of those are missing from the building machine and offer
-    # advice to the user for getting dart-gui-osg to build.
-    find_package(OpenThreads QUIET)
-    if(OPENTHREADS_FOUND)
-      set(warning_msg "Could NOT find OpenSceneGraph")
-    else()
-      if(OSG_LIBRARY)
-        set(warning_msg "Could NOT find OpenThreads")
-      else()
-        set(warning_msg "Could NOT find OpenSceneGraph nor OpenThreads")
-      endif()
-    endif()
-    message(WARNING "${warning_msg} -- we will skip dart-gui-osg\n"
-            "If you believe you do have both OSG and OpenThreads installed, try setting OSG_DIR")
-    return()
-  endif()
-
+  dart_find_package(OpenSceneGraph)
+  dart_check_optional_package(OpenSceneGraph "dart-gui-osg" "OpenSceneGraph" "3.0")
 else()
-
   message(STATUS "Skipping OpenSceneGraph (DART_BUILD_GUI_OSG == ${DART_BUILD_GUI_OSG})")
   return()
-
 endif()
 
 # Search all header and source files
@@ -78,20 +37,13 @@ add_subdirectory(render)
 
 # Add target
 dart_add_library(${target_name} ${hdrs} ${srcs} ${dart_gui_osg_hdrs} ${dart_gui_osg_srcs})
-target_include_directories(
-  ${target_name} SYSTEM
-  PUBLIC ${OPENSCENEGRAPH_INCLUDE_DIRS}
-)
-target_link_libraries(
-  ${target_name}
-  dart-gui
-  ${OPENSCENEGRAPH_LIBRARIES}
-)
+target_link_libraries(${target_name} dart-gui osg::osg)
 
 # Component
 add_component(${PROJECT_NAME} ${component_name})
 add_component_targets(${PROJECT_NAME} ${component_name} ${target_name})
 add_component_dependencies(${PROJECT_NAME} ${component_name} gui)
+add_component_dependency_packages(${PROJECT_NAME} ${component_name} OpenSceneGraph)
 
 # Generate header for this namespace
 dart_get_filename_components(header_names "gui osg headers" ${hdrs})