This is part 3 of my HowTo: SDL on Android series.
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Now let’s get some more native libraries linked into our app.  I probably don’t have to tell you how important this is, since you can’t make a whole lot of games or apps without text, sound, or music.

SDL_ttf

Adding a satellite library like SDL_ttf leads us through several steps.  These are roughly the same for each library, so I’ll only go over this one in specifics.

1) Download the source. Get the latest source from the Mercurial repository or grab a snapshot from the official page.

2) Place source in project. Put the SDL_ttf source directory alongside your SDL directory in your project (in jni/ so you get jni/SDL_ttf).

3) Gather dependencies. The way everything is set up, you have to be particular about the directory placement and naming.  The SDL extension libraries mostly expect their dependency directories to be in jni/ and to be named in their simple form (e.g. libDependency-0.3.0/ would be dependency/).  For SDL_ttf, we need to get the FreeType2 library.  Go to the FreeType official downloads.  You might end up in a list of files to download.  The latest version should be good.  As of this writing, that is “freetype-2.4.11.tar.gz” (you don’t need the doc or demo archives).  Yeah, you’ll probably need a good unzip program that can handle tar.gz or tar.bz2 archives.  Now, SDL_ttf strangely expects FreeType to live within the SDL_ttf directory.  Copy or move it over into the jni/SDL_ttf directory and rename it to “freetype”.

4) Add include and linker flags for the library. Open up your jni/src/Android.mk file.  Add $(LOCAL_PATH)/../SDL_ttf to the LOCAL_C_INCLUDES line.  That will give all of our files access to the SDL_ttf.h header. SDL_ttf knows how to build itself (it has an Android.mk), so it will create a shared library that we can link to.  Add SDL2_ttf (note the “2”) to the LOCAL_SHARED_LIBRARIES line.  The library is linked as SDL2_ttf so you can install it alongside SDL_ttf built for SDL1.2 as necessary.

5) Tell SDL to load the library at runtime. The last thing is to get the C library loaded from the Java code that really drives the app.  Open up src/org/libsdl/app/SDLActivity.java.  In the SDLActivity class, there’s a static block (line 58 in my copy) that loads the .so files.  Uncomment or add the line:

System.loadLibrary("SDL2_ttf");

Now when ndk-build runs, it should pull in SDL_ttf and pump out the .so.  Then when the .apk is installed and run, the Java code will load the C library for you.  Now you can work with the library just as usual.

If you have anything to add, please let me know in the comments!

Tags: android, SDL, SDL2