Make SDL2Config.cmake export SDL2_LIBRARIES etc (on Windows)

still WIP and other platforms than windows still TODO and open
questions etc

see https://github.com/libsdl-org/SDL/issues/4004

SDL2Config.cmake

@@ -1 +1,96 @@
 include("${CMAKE_CURRENT_LIST_DIR}/SDL2Targets.cmake")
+
+
+# cuts off the path at the last (back)slash
+function(my_dirname FILEPATH RETVAL)
+	string(FIND ${FILEPATH} "/" slashPos REVERSE)
+	string(FIND ${FILEPATH} "\\" bsPos REVERSE) # TODO: untested, cmake always gave me forward slashes
+	if(DEFINED slashPos)
+		if( (DEFINED bsPos) AND (${bsPos} GREATER ${slashPos}) )
+			set(slashPos, ${bsPos})
+		endif()
+	elseif(DEFINED bsPos)
+		set(slashPos, ${bsPos})
+	endif()
+	if(DEFINED slashPos)
+		string(SUBSTRING ${FILEPATH} 0 ${slashPos} dirname)
+		set(${RETVAL} ${dirname} PARENT_SCOPE)
+	endif()
+endfunction()
+
+
+if(WIN32)
+	# this seems to work for both MSVC and MINGW+MSYS and with both SDL2Config/Target.cmake from vcpkg
+	# and from building myself with cmake from latest git
+
+	# ok, the headers are easy - but note that this adds both .../include and .../include/SDL2/
+	# while the SDL2_INCLUDE_DIRS of sdl2-config.cmake only add ...include/SDL2/
+	# But at least if building worked with sdl2-config.cmake it will also work with this.
+	get_target_property(SDL2_INCLUDE_DIRS SDL2::SDL2 INTERFACE_INCLUDE_DIRECTORIES)
+
+	# get the paths to the .lib files for both SDL2 and SDL2main
+	# they could be in lots of different properties..
+	get_target_property(sdl2implib SDL2::SDL2 IMPORTED_IMPLIB_RELEASE)
+	get_target_property(sdl2implibdbg SDL2::SDL2 IMPORTED_IMPLIB_DEBUG)
+
+	# TODO: for all this bla_RELEASE bla_DEBUG etc stuff, maybe only try the ones
+	#       from get_target_property(available_configs SDL2::SDL2 IMPORTED_CONFIGURATIONS) ?
+	#       OR otherwise at least try all of NOCONFIG, RELEASE, MINSIZEREL, RELWITHDEBINFO, DEBUG  (possibly in that order)?
+
+	get_target_property(sdl2mainimplib SDL2::SDL2main IMPORTED_IMPLIB_RELEASE)
+	if(NOT sdl2mainimplib)
+		get_target_property(sdl2mainimplib SDL2::SDL2main IMPORTED_LOCATION_RELEASE)
+	endif()
+	get_target_property(sdl2mainimplibdbg SDL2::SDL2main IMPORTED_IMPLIB_DEBUG)
+	if(NOT sdl2mainimplibdbg)
+		get_target_property(sdl2mainimplibdbg SDL2::SDL2main IMPORTED_LOCATION_DEBUG)
+	endif()
+	
+	if( sdl2implib AND sdl2mainimplib AND sdl2implibdbg AND sdl2mainimplibdbg )
+		# we have both release and debug builds of SDL2 and SDL2main, so use this ugly
+		# generator expression in SDL2_LIBRARIES to support both in MSVC, depending on build type configured there
+		set(SDL2_LIBRARIES $<IF:$<CONFIG:Debug>,${sdl2mainimplibdbg},${sdl2mainimplib}>   $<IF:$<CONFIG:Debug>,${sdl2implibdbg},${sdl2implib}>)
+	else()
+		if(NOT sdl2implib) # try to get it from other properties
+			foreach(prop IMPORTED_IMPLIB IMPORTED_IMPLIB_NOCONFIG IMPORTED_IMPLIB_DEBUG IMPORTED_LOCATION_RELEASE IMPORTED_LOCATION_DEBUG)
+				get_target_property(sdl2implib SDL2::SDL2 ${prop})
+				if(sdl2implib)
+					message(STATUS "succeeded with ${prop} => ${sdl2implib}")
+					break()
+				endif()
+				message(STATUS "no luck with ${prop}")
+			endforeach()
+		endif()
+		if(NOT sdl2mainimplib)
+			foreach(prop IMPORTED_IMPLIB IMPORTED_IMPLIB_NOCONFIG IMPORTED_IMPLIB_DEBUG IMPORTED_LOCATION_RELEASE IMPORTED_LOCATION_DEBUG)
+				get_target_property(sdl2mainimplib SDL2::SDL2main ${prop})
+				if(sdl2mainimplib)
+					message(STATUS "succeeded with ${prop} => ${sdl2mainimplib}")
+					break()
+				endif()
+				message(STATUS "no luck with ${prop}")
+			endforeach()
+		endif()
+		
+		if( sdl2implib AND sdl2mainimplib )
+				set(SDL2_LIBRARIES ${sdl2mainimplib}  ${sdl2implib})
+		else()
+				message(FATAL_ERROR, "SDL2::SDL2 and/or SDL2::SDL2main don't seem to contain any kind of IMPORTED_IMPLIB")
+		endif()
+	endif()
+
+	# NOTE: SDL2_LIBRARIES now looks like "c:/path/to/SDL2main.lib;c:/path/to/SDL2.lib"
+	#       which is different to what it looks like when coming from sdl2-config.cmake
+	#       (there it's more like "-L${SDL2_LIBDIR} -lSDL2main -lSDL2" - and also -lmingw32 and -mwindows)
+	#       This seems to work with both MSVC and MinGW though, while the other only worked with MinGW
+
+	my_dirname(${sdl2implib} SDL2_LIBDIR)
+
+	my_dirname(${SDL2_LIBDIR} SDL2_EXEC_PREFIX) # the exec prefix is one level up from lib/ - TODO: really, always? at least on Linux there's /usr/lib/x86_64-bla-blub/libSDL2-asdf.so.0 ..
+	set(SDL2_PREFIX ${SDL2_PREFIX}) # TODO: could this be somewhere else? parent dir of include or sth?
+
+elseif() # not windows
+	# TODO: about the same but don't have to look at *_IMPLIB* as that's windows specific, it should be in IMPORTED_LOCATION*
+	# TODO: make SDL2_LIBRARIES look more like the original (instead of path to libSDL2.so)?
+	# TODO: anything special about macOS? I can't test that, I have no Mac
+endif()

sdl2-config.cmake.in

@@ -23,7 +23,8 @@ if(NOT TARGET SDL2::SDL2)
     INTERFACE_INCLUDE_DIRECTORIES "@includedir@/SDL2"
     IMPORTED_LINK_INTERFACE_LANGUAGES "C"
     IMPORTED_LOCATION "@libdir@/${CMAKE_SHARED_LIBRARY_PREFIX}SDL2${CMAKE_SHARED_LIBRARY_SUFFIX}"
-    INTERFACE_LINK_LIBRARIES "${SDL2_EXTRA_LINK_FLAGS}")
+    # TODO: on windows set IMPORTED_IMPLIB to SDL2.lib
+    INTERFACE_LINK_LIBRARIES "${SDL2_EXTRA_LINK_FLAGS}") # TODO: really? SDL2Config.cmake doesn't do this
 
   add_library(SDL2::SDL2-static STATIC IMPORTED)
   set_target_properties(SDL2::SDL2-static PROPERTIES