Fri 27 June 2008

MikMod library ported to iPhone


I've always been a big fan of old skool computer music, like chiptunes or demoscene music. Perhaps because they remind me the Good Old Days (tm) of my Amiga. Or perhaps for the same reason I like demoscene: real-time computer art! Because it's definitely cool, I've decided to port MikMod to the iPhone! We'll see later if it might be useful to someone else :)

Compiling libmikmod

Here are the steps to follow to build libmikmod for your iPhone or iPod Touch. First of all, make sure that you have the necessary header file from Apple, namely AudioQueue.h. This file is part of the AudioQueue framework, which is available in the MacOS X 10.5 SDK. This means that the official iPhone SDK is not required. Then, download the latest libmikmod-3.2.0-beta2 available on the MikMod homepage, as well as this patch for iPhone support. For simplicity, let's consider that both files will be downloaded in the same directory. Once you have them, extract the archive and apply the patch:

tar -zxf libmikmod-3.2.0-beta2.tar.gz
cd libmikmod-3.2.0-beta2
gunzip -cd ../iphone-drv-mikmod-3.2.0-beta2.patch.gz | patch -p1

Among other things, the patch modifies various Makefiles and the configure script, so we have to cleanly regenerate all the autotool-related files:


Now let's set up the necessary environment variables to configure and build libmikmod. First, where to find the AudioQueue header and where to install libmikmod:

export AQDIR=$HOME/local/audioqueue
export MMDIR=$HOME/local/mikmod-iphone

Make sure you are using absolute paths for the variables above. Then, let's set up some compilation flags and name the tools we'll use from the iPhone toolchain:

export LDFLAGS="-framework AudioToolbox"
export CC=arm-apple-darwin-gcc
export RANLIB=arm-apple-darwin-ranlib

Okay, now it's time to let configure do its job:

./configure --enable-iphone --host=arm-apple-darwin --disable-oss --disable-esd --prefix=$MMDIR

We're almost done! But there's still a little quirk that must be addressed. The project is configured to build shared libraries, which for some reason refuse to link with the version of the open-source iPhone toolchain I use. To overcome this problem, you just need to patch the generated libtool configuration. Knowing no clever means to do so, I propose something like:

sed -r -i 's/^(allow_undefined_flag.*)"/\1 -Wl,-read_only_relocs,suppress"/' libtool

Phew, now we're done! Just type:

make install

And voila! a fresh libmikmod with support for your beloved iPhone or iPod Touch! Oh, by the way: the library comes in both static and dynamic flavor, so it should be pretty usable. Of course, the obligatory example will follow soon :P EDIT: the link to the patch was pointing to a plain file instead of a gzip one, fixed!