support static link of SDL2 and pkg-config

Add SDL2_STATIC variable, when set to ON will link the static version of
SDL2 and add any necessary libs and linker flags for linking it
statically from pkg-config. All extra libs and linker flags are added to
SDL2_LIBRARY, so the user does not need to do anything except set that
flag.

For dynamic linking, any extra stuff from pkg-config is also retrieved
and added to SDL2_LIBRARY.

The variable SDL2_DEFINITIONS is also retrieved from
`pkg-config --cflags-only-other`. The user needs to call ADD_DEFINITIONS
for it, the documentation is updated to reflect this.

If pkg-config is not available, the module functions as before with no
errors, but SDL2_STATIC will probably fail.

TODO:

* warn if pkg-config is not found

* add similar code to the other two cmake modules, or factor it out

* support sdl2-config as well (extra parsing)

Author: rkitover

FindSDL2.cmake

@@ -1,9 +1,22 @@
-
 # This module defines
 # SDL2_LIBRARY, the name of the library to link against
 # SDL2_FOUND, if false, do not try to link to SDL2
 # SDL2_INCLUDE_DIR, where to find SDL.h
 #
+# If you have pkg-config, these extra variables are also defined:
+# SDL2_DEFINITIONS, extra CFLAGS
+# SDL2_EXTRA_LIBS, extra link libs
+# SDL2_LINKER_FLAGS, extra link flags
+#
+# The latter two are automatically added to SDL2_LIBRARY
+#
+# To use them, add code such as:
+#
+# # SET(SDL2_STATIC ON) # if you want to link SDL2 statically
+# FIND_PACKAGE(SDL2 REQUIRED)
+# ADD_DEFINITIONS(${SDL2_DEFINITIONS})
+# TARGET_LINK_LIBRARIES(your-executable-target ${SDL2_LIBRARY} ...)
+#
 # This module responds to the the flag:
 # SDL2_BUILDING_LIBRARY
 # If this is defined, then no SDL2main will be linked in because
@@ -12,6 +25,8 @@
 # module will attempt to locate and set the the proper link flags
 # as part of the returned SDL2_LIBRARY variable.
 #
+# If you want to link SDL2 statically, set SDL2_STATIC to ON.
+#
 # Don't forget to include SDLmain.h and SDLmain.m your project for the
 # OS X framework based version. (Other versions link to -lSDL2main which
 # this module will try to find on your behalf.) Also for OS X, this
@@ -47,7 +62,7 @@
 # SDL2_LIBRARY to override this selection or set the CMake environment
 # CMAKE_INCLUDE_PATH to modify the search paths.
 #
-# Note that the header path has changed from SDL2/SDL.h to just SDL.h
+# Note that the header path has changed from SDL3/SDL.h to just SDL.h
 # This needed to change because "proper" SDL convention
 # is #include "SDL.h", not <SDL2/SDL.h>. This is done for portability
 # reasons because not all systems place things in SDL2/ (see FreeBSD).
@@ -86,6 +101,16 @@ FIND_PATH(SDL2_INCLUDE_DIR SDL.h
 	PATHS ${SDL2_SEARCH_PATHS}
 )
 
+SET(CURRENT_FIND_LIBRARY_SUFFIXES ${CMAKE_FIND_LIBRARY_SUFFIXES})
+
+IF(SDL2_STATIC)
+    IF(WIN32)
+        SET(CMAKE_FIND_LIBRARY_SUFFIXES .lib .a)
+    ELSE(WIN32)
+        SET(CMAKE_FIND_LIBRARY_SUFFIXES .a)
+    ENDIF(WIN32)
+ENDIF(SDL2_STATIC)
+
 FIND_LIBRARY(SDL2_LIBRARY_TEMP
 	NAMES SDL2
 	HINTS
@@ -110,6 +135,9 @@ IF(NOT SDL2_BUILDING_LIBRARY)
 	ENDIF(NOT ${SDL2_INCLUDE_DIR} MATCHES ".framework")
 ENDIF(NOT SDL2_BUILDING_LIBRARY)
 
+SET(CMAKE_FIND_LIBRARY_SUFFIXES ${CURRENT_FIND_LIBRARY_SUFFIXES})
+UNSET(CURRENT_FIND_LIBRARY_SUFFIXES)
+
 # SDL2 may require threads on your system.
 # The Apple build may not need an explicit flag because one of the
 # frameworks may already provide it.
@@ -154,6 +182,37 @@ IF(SDL2_LIBRARY_TEMP)
 		SET(SDL2_LIBRARY_TEMP ${MINGW32_LIBRARY} ${SDL2_LIBRARY_TEMP})
 	ENDIF(MINGW)
 
+        # Add some stuff from pkg-config, if available
+        IF(NOT PKG_CONFIG_EXECUTABLE)
+            FIND_PACKAGE(PkgConfig QUIET)
+        ENDIF(NOT PKG_CONFIG_EXECUTABLE)
+
+        IF(PKG_CONFIG_EXECUTABLE)
+            # get any definitions
+            EXECUTE_PROCESS(COMMAND ${PKG_CONFIG_EXECUTABLE} --cflags-only-other sdl2 OUTPUT_VARIABLE SDL2_DEFINITIONS)
+
+            SET(SDL2_DEFINITIONS ${SDL2_DEFINITIONS} CACHE STRING "Extra CFLAGS for SDL2 from pkg-config")
+
+            # get any extra stuff needed for linking
+            IF(NOT SDL2_STATIC)
+                EXECUTE_PROCESS(COMMAND ${PKG_CONFIG_EXECUTABLE}          --libs-only-other sdl2 OUTPUT_VARIABLE SDL2_LINKER_FLAGS_RAW    OUTPUT_STRIP_TRAILING_WHITESPACE)
+
+                EXECUTE_PROCESS(COMMAND ${PKG_CONFIG_EXECUTABLE}          --libs-only-l     sdl2 OUTPUT_VARIABLE SDL2_EXTRA_LIBS_RAW      OUTPUT_STRIP_TRAILING_WHITESPACE)
+            ELSE(NOT SDL2_STATIC)
+                EXECUTE_PROCESS(COMMAND ${PKG_CONFIG_EXECUTABLE} --static --libs-only-other sdl2 OUTPUT_VARIABLE SDL2_LINKER_FLAGS_RAW    OUTPUT_STRIP_TRAILING_WHITESPACE)
+                EXECUTE_PROCESS(COMMAND ${PKG_CONFIG_EXECUTABLE} --static --libs-only-l     sdl2 OUTPUT_VARIABLE SDL2_EXTRA_LIBS_RAW      OUTPUT_STRIP_TRAILING_WHITESPACE)
+            ENDIF(NOT SDL2_STATIC)
+
+            STRING(REGEX REPLACE "[^ ]+SDL2[^ ]*" ""  SDL2_EXTRA_LIBS_RAW2 "${SDL2_EXTRA_LIBS_RAW}")
+            STRING(REGEX REPLACE " +"             ";" SDL2_EXTRA_LIBS      "${SDL2_EXTRA_LIBS_RAW2}")
+            STRING(REGEX REPLACE " +"             ";" SDL2_LINKER_FLAGS    "${SDL2_LINKER_FLAGS_RAW}")
+
+            SET(SDL2_LINKER_FLAGS ${SDL2_LINKER_FLAGS} CACHE STRING "Linker flags for linking SDL2")
+            SET(SDL2_EXTRA_LIBS   ${SDL2_EXTRA_LIBS}   CACHE STRING "Extra libraries for linking SDL2")
+
+            SET(SDL2_LIBRARY_TEMP ${SDL2_LIBRARY_TEMP} ${SDL2_EXTRA_LIBS} ${SDL2_LINKER_FLAGS})
+        ENDIF(PKG_CONFIG_EXECUTABLE)
+
 	# Set the final string here so the GUI reflects the final state.
 	SET(SDL2_LIBRARY ${SDL2_LIBRARY_TEMP} CACHE STRING "Where the SDL2 Library can be found")
 	# Set the temp variable to INTERNAL so it is not seen in the CMake GUI

readme.md

@@ -28,7 +28,12 @@ where `project` is the name of your project. You can then use the packages
 themselves by adding
 
 ```cmake
+set(SDL2_STATIC OFF) # on to link it statically
+
 find_package(SDL2 REQUIRED)
+
+add_definitions(${SDL2_DEFINITIONS})
+
 find_package(SDL2_Image REQUIRED)
 find_package(SDL2_ttf REQUIRED)