Add: introduce CMake for project management

CMake works on all our supported platforms, like MSVC, Mingw, GCC,
Clang, and many more. It allows for a single way of doing things,
so no longer we need shell scripts and vbs scripts to work on all
our supported platforms.

Additionally, CMake allows to generate project files for like MSVC,
KDevelop, etc.

This heavily reduces the lines of code we need to support multiple
platforms from a project perspective.

Addtiionally, this heavily improves our detection of libraries, etc.

1 files changed, 63 insertions, 0 deletions

diff --git a/cmake/SourceList.cmake b/cmake/SourceList.cmake
new file mode 100644
index 000000000..6300a19a4
--- /dev/null
+++ b/cmake/SourceList.cmake
@@ -0,0 +1,63 @@
+# Add a file to be compiled.
+#
+# add_files([file1 ...] CONDITION condition [condition ...])
+#
+# CONDITION is a complete statement that can be evaluated with if().
+# If it evaluates true, the source files will be added; otherwise not.
+# For example: ADD_IF SDL_FOUND AND Allegro_FOUND
+#
+function(add_files)
+    cmake_parse_arguments(PARAM "" "" "CONDITION" ${ARGN})
+    set(PARAM_FILES "${PARAM_UNPARSED_ARGUMENTS}")
+
+    if (PARAM_CONDITION)
+        if (NOT (${PARAM_CONDITION}))
+            return()
+        endif (NOT (${PARAM_CONDITION}))
+    endif (PARAM_CONDITION)
+
+    foreach(FILE IN LISTS PARAM_FILES)
+        target_sources(openttd PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/${FILE})
+    endforeach()
+endfunction(add_files)
+
+# This function works around an 'issue' with CMake, where
+# set_source_files_properties() only works in the scope of the file. We want
+# to set properties for the source file on a more global level. To solve this,
+# this function records the flags you want, and a macro adds them in the root
+# CMakeLists.txt.
+# See this URL for more information on the issue:
+# http://cmake.3232098.n2.nabble.com/scope-of-set-source-files-properties-td4766111.html
+#
+# set_compile_flags([file1 ...] COMPILE_FLAGS cflag [cflag ...])
+#
+function(set_compile_flags)
+    cmake_parse_arguments(PARAM "" "" "COMPILE_FLAGS" ${ARGN})
+    set(PARAM_FILES "${PARAM_UNPARSED_ARGUMENTS}")
+
+    get_property(SOURCE_PROPERTIES GLOBAL PROPERTY source_properties)
+
+    foreach(FILE IN LISTS PARAM_FILES)
+        list(APPEND SOURCE_PROPERTIES "${CMAKE_CURRENT_SOURCE_DIR}/${FILE}::${PARAM_COMPILE_FLAGS}")
+    endforeach()
+
+    set_property(GLOBAL PROPERTY source_properties "${SOURCE_PROPERTIES}")
+endfunction(set_compile_flags)
+
+# Call this macro in the same CMakeLists.txt and after add_executable().
+# This makes sure all the COMPILE_FLAGS of set_compile_flags() are set
+# correctly.
+#
+# process_compile_flags()
+#
+function(process_compile_flags)
+    get_property(SOURCE_PROPERTIES GLOBAL PROPERTY source_properties)
+
+    foreach(ENTRY ${SOURCE_PROPERTIES})
+        string(REPLACE "::" ";" ENTRY "${ENTRY}")
+        list(GET ENTRY 0 FILE)
+        list(GET ENTRY 1 PROPERTIES)
+
+        set_source_files_properties(${FILE} PROPERTIES COMPILE_FLAGS ${PROPERTIES})
+    endforeach()
+endfunction(process_compile_flags)