Add unity build option

Each component and each MW-subsystem will be used as a single compilation unit.

CMakeLists.txt

@@ -73,6 +73,8 @@ option(OGRE_STATIC  "Link static build of Ogre and Ogre Plugins into the binarie
 option(BOOST_STATIC "Link static build of Boost into the binaries" FALSE)
 option(SDL2_STATIC "Link static build of SDL into the binaries" FALSE)
 
+option(OPENMW_UNITY_BUILD "Use fewer compilation units to speed up compile time" FALSE)
+
 # Apps and tools
 option(BUILD_BSATOOL "build BSA extractor" OFF)
 option(BUILD_ESMTOOL "build ESM inspector" ON)

cmake/OpenMWMacros.cmake

@@ -1,26 +1,75 @@
+function(enable_unity_build UB_SUFFIX SOURCE_VARIABLE_NAME)
+    set(files ${SOURCE_VARIABLE_NAME})
+    # Generate a unique filename for the unity build translation unit
+    set(unit_build_file ${CMAKE_CURRENT_BINARY_DIR}/ub_${UB_SUFFIX}.cpp)
+    # Exclude all translation units from compilation
+    set_source_files_properties(${files} PROPERTIES HEADER_FILE_ONLY true)
+    # Open the ub file
+        FILE(WRITE ${unit_build_file} "// Unity Build generated by CMake\n")
+    # Add include statement for each translation unit
+    foreach(source_file ${files} )
+        FILE( APPEND ${unit_build_file} "#include <${source_file}>\n")
+    endforeach(source_file)
+    # Complement list of translation units with the name of ub
+    set(${SOURCE_VARIABLE_NAME} ${${SOURCE_VARIABLE_NAME}} ${unit_build_file} PARENT_SCOPE)
+endfunction(enable_unity_build)
+
+
 
 macro (add_openmw_dir dir)
-set (files)
-foreach (u ${ARGN})
-file (GLOB ALL "${dir}/${u}.[ch]pp")
-foreach (f ${ALL})
-list (APPEND files "${f}")
-list (APPEND OPENMW_FILES "${f}")
-endforeach (f)
-endforeach (u)
-source_group ("apps\\openmw\\${dir}" FILES ${files})
+    set (files)
+    set (cppfiles)
+    foreach (u ${ARGN})
+
+        # Add cpp and hpp to OPENMW_FILES
+        file (GLOB ALL "${dir}/${u}.[ch]pp")
+        foreach (f ${ALL})
+            list (APPEND files "${f}")
+            list (APPEND OPENMW_FILES "${f}")
+        endforeach (f)
+
+        # Add cpp to unity build
+        file (GLOB ALL "${dir}/${u}.cpp")
+        foreach (f ${ALL})
+            list (APPEND cppfiles "${f}")
+        endforeach (f)
+
+    endforeach (u)
+
+    if (OPENMW_UNITY_BUILD)
+        enable_unity_build(${dir} "${cppfiles}")
+        list (APPEND OPENMW_FILES ${CMAKE_CURRENT_BINARY_DIR}/ub_${dir}.cpp)
+    endif()
+
+    source_group ("apps\\openmw\\${dir}" FILES ${files})
 endmacro (add_openmw_dir)
 
 macro (add_component_dir dir)
-set (files)
-foreach (u ${ARGN})
-file (GLOB ALL "${dir}/${u}.[ch]pp")
-foreach (f ${ALL})
-list (APPEND files "${f}")
-list (APPEND COMPONENT_FILES "${f}")
-endforeach (f)
-endforeach (u)
-source_group ("components\\${dir}" FILES ${files})
+    set (files)
+    set (cppfiles)
+
+    foreach (u ${ARGN})
+        file (GLOB ALL "${dir}/${u}.[ch]pp")
+
+        foreach (f ${ALL})
+            list (APPEND files "${f}")
+            list (APPEND COMPONENT_FILES "${f}")
+        endforeach (f)
+
+        # Add cpp to unity build
+        file (GLOB ALL "${dir}/${u}.cpp")
+        foreach (f ${ALL})
+            list (APPEND cppfiles "${f}")
+        endforeach (f)
+
+    endforeach (u)
+
+    if (OPENMW_UNITY_BUILD)
+        enable_unity_build(${dir} "${cppfiles}")
+        list (APPEND COMPONENT_FILES ${CMAKE_CURRENT_BINARY_DIR}/ub_${dir}.cpp)
+    endif()
+
+    source_group ("components\\${dir}" FILES ${files})
 endmacro (add_component_dir)
 
 macro (add_component_qt_dir dir)