Cross Compiling and Interopping with Open Source Text-to-Speech (TTS) C libraries for iPhone.

1. How to compile Open Source projects to work as libraries with the iPhone.

By no means is this an indepth or high level discussion on this subject.  This is merely an example of one OpenSource project I managed to compile for the Arm6 iPhone processor.  I have no reason to believe it would not be successful in other projects, but I'm certain that not all C and C++ projects are created equal.

Theoretically, if a project is programmed well in C or C++, it should work and compile for the Arm6 processor.  Note above "If a project is programmed well," and also note that this is GREATLY simplifying what has to happen in the original developer's build and programming to have a project to be able to universally cross-compile above.  This won't always be the case. 

However, for the most part, many good OpenSource C and C++ projects shouldn't have too great a difficulty being cross compiled for the iPhone platform.  Often times, you'll find that the project even has a 'lite' version specifically designed for mobile processors, with handy stuff like power reduction optimizations built in.

Posted below is a very handy script I found to do the heavy-lifting for me.  The script uses GCC Make to do its work.  You will need to edit a few lines to address the version of GCC and G++ you want to use in the configure strings below, as well as what version of the iPhone SDK you want to use in the compile.

 #!/bin/sh

# build_fat.sh
#
# Created by Robert Carlsen on 15.07.2009.
# build an arm / i686 lib of standard linux project
#
# adopted from: http://latenitesoft.blogspot.com/200...ding-unix.html
#
# initially configured for tesseract-ocr

# Set up the target lib file / path
# easiest to just build the package normally first and watch where the files are created.
LIBFILE=ccmain/libtesseract_full

# Select the desired iPhone SDK
export DEVROOT=/Developer/Platforms/iPhoneOS.platform/Developer
export SDKROOT=$DEVROOT/SDKs/iPhoneOS3.0.sdk

# Set up relevant environment variables
export CPPFLAGS="-I$SDKROOT/usr/lib/gcc/arm-apple-darwin9/4.0.1/include/ -I$SDKROOT/usr/include/"
export CFLAGS="$CPPFLAGS -arch armv6 -pipe -no-cpp-precomp -isysroot $SDKROOT"
export CPP="$DEVROOT/usr/bin/cpp $CPPFLAGS"
export CXXFLAGS="$CFLAGS"

# Dynamic library location generated by the Unix package
LIBPATH=$LIBFILE.dylib
LIBNAME=`basename $LIBPATH`

export LDFLAGS="-L$SDKROOT/usr/lib/ -Wl,-dylib_install_name,@executable_path/$LIBNAME"

# Static library that will be generated for ARM
LIBPATH_static=$LIBFILE.a
LIBNAME_static=`basename $LIBPATH_static`

# TODO: add custom flags as necessary for package
./configure CXX=$DEVROOT/usr/bin/arm-apple-darwin9-g++-4.0.1 CC=$DEVROOT/usr/bin/arm-apple-darwin9-gcc-4.0.1 LD=$DEVROOT/usr/bin/ld --host=arm-apple-darwin

make -j4

# Copy the ARM library to a temporary location
mkdir -p lnsout
cp $LIBPATH_static lnsout/$LIBNAME_static.arm

# Do it all again for native cpu
make distclean

# Restore default environment variables
unset CPPFLAGS CFLAGS CPP LDFLAGS CXXFLAGS

# Overwrite LDFLAGS
# Dynamic linking, relative to executable_path
# Use otool -D to check the install name
export LDFLAGS="-Wl,-dylib_install_name,@executable_path/$LIBNAME"

# TODO: error checking
./configure
make -j4

# Copy the native library to the temporary location
cp $LIBPATH_static lnsout/$LIBNAME_static.i386

# Create fat lib by combining the two versions
#$DEVROOT/usr/bin/lipo -arch arm lnsout/$LIBNAME_static.arm -arch i386 lnsout/$LIBNAME_static.i386 -create #-output lnsout/$LIBNAME_static


 Link to Script's Original site:

2. Interopping with Flite Text-to-Speech (TTS) libraries with MonoTouch C# for the iPhone

To interop with the Flite libraries, you'll need to add the four libraries below to your project that Flite requires to run:

TextToWave.cs class - Where the Interop Magic happens:

This is the class (with a bunch of comments, some redundant) that I wrote as a wrapper for the DLL.

It's dirty, but you'll get the idea.

using System;
using System.Runtime.InteropServices;

namespace VoiceTest123
{

    // You should to create a new class to deal with wrapping each native library you need to call        //  functions from,
    // because you'll ultimately want to have a classname.functionname way of calling the library.
    
    public class TextToWave
    {
        
    // Dllimport function from System.Runtime.InteropServices
    // For this application, you import the DLL through GCC flags and call it via

    //  [Dllimport "__Internal")].  This is because
    // Monotouch statically compiles everything, so you're actually declaring the function whose body     // is INSIDE the Native Library (after compiliation)        
    
    // This first function is in libflite.a, the compiled C library you're linking up with.  
    // Research Cross Compiling to find out how to convert C and C++ projects to the iPhone Arm6          // processor.
        
    // Any native library must be compiled into a .a extension for the Arm6 processor on the iPhone:
    // HOWEVER!!! NOTE:  When you use the iPhone simluator to debug this, you must use a library that     // was compiled for
    // the 1386 processor in order for it to work.
    // This is where I learned that the iPhone simulator is NOT an iPhone emulator.
        
        
    // This first DllImport deals with the first function called in libflite.a
  

  [DllImport ("__Internal")]
                
        //  The flite_init function of the library must be called before any other function in the         //  library towork.
        //  This is to allow room to  for the flite devs build in future functionality, and right now         //  does nothing more than allow the rest of the functions to be called after its activation.


        static extern void flite_init ();
        
        public void fliteInitFunc() {
            flite_init();
        }

        //  You must do a new DllImport for each function you link up inside your class to the C         //  libraries.  This second link creates an IntPtr to the library where the "Computerized         //  Voice Object" lives.

        [DllImport ("__Internal")]
                

        //  Esentially, for each one of these voice libraries you have, you'll have a different                //  "person's" voice.
        //  This is how you can modularly change the voice sound, clarity, gender, age, etc, of the         //  voice.
        //  The register_cmu_us_kal function is a function in the c library - any of these voices will         //  have a register_cmu_country_name function will exist in any properly made voice library         //  for flite.
        
        static extern IntPtr register_cmu_us_kal();
        
        //  Third Dllimport to link flite_text_to_speech
        [DllImport ("__Internal")]
        
        //  Actual C Function in libflite.a that you're calling:
        //  float flite_text_to_speech(const char *text, cst_voice *voice, const char *outtype);
        
        //  The three arguments this function takes are: The string you're outputting to voice,
        //  the voice library you've declared above for use, and the output type you want.
        //  There are three out-types, but I'm only certain that one works for the iPhone at this         //  time.


        //  You can set the out-type to play directly to the device using the argument "play" (Proven         //  not working 'out of the box" 
        //  you can set it to write to the file system by providing a path string )This works, and is         //  how I call it later to be replayed- just record the .wav file, and then play it using the         //  Mono-touch API. 

        //  Or you you can set it to none.  Not sure why you'd need that, but you have the option.
        //  I have only tested this with output to the filesystem
        
        static extern void flite_text_to_speech (string arg1, IntPtr register_cmu_us_kal, string _ arg2);
        
        
        //  The function to call all the functionalties above to output a text string to speech:
        
        public void ConvertTextToWav(string arg3, string arg4) {    

  //  Call first required init function to allow to call the rest              
        fliteInitFunc();    
  

  //  Call Flite Text to Speech function     
        flite_text_to_speech (arg3, register_cmu_us_kal(), arg4);
                                            
        }
        
        
    }
}

 Here's an example Button event delgate that can call your output -

                        button.TouchUpInside += delegate {

                                string textToSpeak = textField.Text;

                              

                                var basedir = Path.Combine (Environment.GetFolderPath) (Environment.SpecialFolder.Personal), "..");

                                var tmpdir = Path.Combine(basedir, "tmp");

                              

                                string audioFilePath = Path.Combine(tmpdir, "foo.wav");

                             

                                _speaker.ConvertTextToWav(textToSpeak, audioFilePath);

                              

                                AVAudioPlayer audioPlayer = new _ AVAudioPlayer(NSUrl.FromFilename(audioFilePath), null);

                                audioPlayer.PrepareToPlay();

                                audioPlayer.Play();

                        };