various cmake fixes (#25748)

- enable building in a cmake subdirectory:
    - use consistent path to "etc" in build directory
    - add a quick fix for mavlink inclusion with
      `mavlink/<version>/mavlink.h`, presumably the problem does not
      appear normally since somewhere the build root directory is added
      to include paths.
- install gazebo config and plugins, the goal is to enable packaging of
  PX4 sitl binaries.
- fix dependency on dds_topics.h generation in uxrce_dds_client:
  *** No rule to make target 'PX4-Autopilot/src/modules/uxrce_dds_client/dds_topics.h', needed by 'PX4-Autopilot/events/px4.json'.  Stop.
  https://github.com/PX4/PX4-Autopilot/issues/21788

Co-authored-by: Jacob Dahl <37091262+dakejahl@users.noreply.github.com>

platforms/posix/CMakeLists.txt

@@ -87,7 +87,7 @@ install(
 	DIRECTORY
 		${PROJECT_SOURCE_DIR}/posix-configs
 		${PROJECT_SOURCE_DIR}/test
-		${CMAKE_BINARY_DIR}/etc
+		${PX4_BINARY_DIR}/etc
 		${CMAKE_RUNTIME_OUTPUT_DIRECTORY}
 	DESTINATION
 		${PROJECT_NAME}
@@ -201,6 +201,14 @@ elseif("${PX4_BOARD}" MATCHES "sitl")
 			${PROJECT_NAME}/build/px4_sitl_default
 		)
 
+	# gazebo files
+	install(
+		FILES
+			${PROJECT_SOURCE_DIR}/Tools/simulation/gz/server.config
+		DESTINATION
+			${PROJECT_NAME}/Tools/simulation/gz
+		)
+
 	# gazebo dirs
 	install(
 		DIRECTORY

src/modules/mavlink/CMakeLists.txt

@@ -92,6 +92,7 @@ target_sources(mavlink_c
 target_include_directories(mavlink_c
 	INTERFACE
 		${MAVLINK_LIBRARY_DIR}
+		${MAVLINK_LIBRARY_DIR}/../
 		${MAVLINK_LIBRARY_DIR}/${CONFIG_MAVLINK_DIALECT}
 		${MAVLINK_LIBRARY_DIR}/${MAVLINK_DIALECT_UAVIONIX}
 )

src/modules/simulation/gz_plugins/gstreamer/CMakeLists.txt

@@ -67,4 +67,8 @@ else()
         PRIVATE ${GSTREAMER_CFLAGS}
         PRIVATE ${GSTREAMER_APP_CFLAGS}
     )
+
+    if (NOT CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
+        install(TARGETS ${PROJECT_NAME} LIBRARY DESTINATION lib/px4_gz_plugins)
+    endif()
 endif()

src/modules/simulation/gz_plugins/moving_platform_controller/CMakeLists.txt

@@ -50,3 +50,7 @@ target_include_directories(${PROJECT_NAME}
     PUBLIC ${CMAKE_CURRENT_BINARY_DIR}
     PUBLIC px4_gz_msgs
 )
+
+if (NOT CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
+    install(TARGETS ${PROJECT_NAME} LIBRARY DESTINATION lib/px4_gz_plugins)
+endif()

src/modules/simulation/gz_plugins/optical_flow/CMakeLists.txt

@@ -63,3 +63,7 @@ target_include_directories(${PROJECT_NAME}
 )
 
 add_dependencies(${PROJECT_NAME} OpticalFlow)
+
+if (NOT CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
+    install(TARGETS ${PROJECT_NAME} LIBRARY DESTINATION lib/px4_gz_plugins)
+endif()

src/modules/simulation/gz_plugins/optical_flow/optical_flow.cmake

@@ -35,19 +35,24 @@ include(ExternalProject)
 find_package(OpenCV REQUIRED)
 
 if(NOT TARGET OpticalFlow)
+    if(CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
+        set(OPTICAL_FLOW_INSTALL_PREFIX "${CMAKE_BINARY_DIR}/OpticalFlow/install")
+    else()
+        set(OPTICAL_FLOW_INSTALL_PREFIX "${CMAKE_INSTALL_PREFIX}")
+    endif()
+
     ExternalProject_Add(OpticalFlow
         GIT_REPOSITORY https://github.com/PX4/PX4-OpticalFlow.git
         GIT_TAG master
         PREFIX ${CMAKE_BINARY_DIR}/OpticalFlow
-        INSTALL_DIR ${CMAKE_BINARY_DIR}/OpticalFlow/install
-        CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=<INSTALL_DIR>
-        BUILD_BYPRODUCTS ${CMAKE_BINARY_DIR}/OpticalFlow/install/lib/libOpticalFlow.so
+        INSTALL_DIR ${OPTICAL_FLOW_INSTALL_PREFIX}
+        CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=${OPTICAL_FLOW_INSTALL_PREFIX}
+        BUILD_BYPRODUCTS ${OPTICAL_FLOW_INSTALL_PREFIX}/lib/libOpticalFlow.so
         UPDATE_DISCONNECTED ON
         BUILD_ALWAYS OFF
         STEP_TARGETS build
     )
 
-    ExternalProject_Get_Property(OpticalFlow install_dir)
-    set(OpticalFlow_INCLUDE_DIRS ${install_dir}/include CACHE INTERNAL "")
-    set(OpticalFlow_LIBS ${install_dir}/lib/libOpticalFlow.so CACHE INTERNAL "")
+    set(OpticalFlow_INCLUDE_DIRS ${OPTICAL_FLOW_INSTALL_PREFIX}/include CACHE INTERNAL "")
+    set(OpticalFlow_LIBS ${OPTICAL_FLOW_INSTALL_PREFIX}/lib/libOpticalFlow.so CACHE INTERNAL "")
 endif()

src/modules/simulation/gz_plugins/template_plugin/CMakeLists.txt

@@ -66,3 +66,7 @@ target_include_directories(${PROJECT_NAME}
 
 # Add dependencies if needed
 # add_dependencies(${PROJECT_NAME} ExternalDependency)
+
+if (NOT CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
+    install(TARGETS ${PROJECT_NAME} LIBRARY DESTINATION lib/px4_gz_plugins)
+endif()

src/modules/uxrce_dds_client/CMakeLists.txt

@@ -63,7 +63,6 @@ else()
 	endif()
 
 	include(ExternalProject)
-
 	ExternalProject_Add(
 		libmicroxrceddsclient_project
 		PREFIX      ${microxrceddsclient_build_dir}
@@ -139,7 +138,6 @@ else()
 			# -DDEBUG_BUILD
 			${MAX_CUSTOM_OPT_LEVEL}
 		SRCS
-			${CMAKE_CURRENT_BINARY_DIR}/dds_topics.h
 			uxrce_dds_client.cpp
 			uxrce_dds_client.h
 			vehicle_command_srv.cpp