Cross Compile OpenCV for Rpi2 with Java bindings - opencv

Question

What I try to do is to cross compile OpenCV from a x86 host machine to an ARM target machine (Raspberry Pi 2) with Java bindings.
All I've achieved is to compile OpenCV with Java bindings for x86 platform, or even OpenCV with NO Java bindings for ARM platform. However I cannot compile OpenCV with Java bindings for ARM platform.
I've kind of followed thousands of guides to do this. This is from OpenCV's official site, and seems to be very simple: http://docs.opencv.org/2.4/doc/tutorials/introduction/crosscompilation/arm_crosscompile_with_cmake.html
My host machine is the following:
$ uname -a:
Linux ubuntu 4.2.0-16-generic #19-Ubuntu SMP Thu Oct 8 14:46:51 UTC 2015 i686 i686 i686 GNU/Linux
I've installed gcc and g++ cross compilation tools (gnueabi and gnueabihf):
$ sudo apt-get install gcc-arm-linux-gnueabi
$ sudo apt-get install g++-arm-linux-gnueabi
$ sudo apt-get install gcc-arm-linux-gnueabihf
$ sudo apt-get install g++-arm-linux-gnueabihf
$ which arm-linux-gnueabihf-gcc
/usr/bin/arm-linux-gnueabihf-gcc
$ which arm-linux-gnueabihf-g++
/usr/bin/arm-linux-gnueabihf-g++
Since I want to compile OpenCV with the Java bindings, I installed jdk and ant:
$ sudo apt-get install openjdk-7-jre
$ sudo apt-get install openjdk-7-jdk
$ sudo apt-get install ant
Then I add these lines to .bashrc file:
JAVA_HOME=/usr/lib/jvm/java-7-openjdk-i386
PATH=$JAVA_HOME/bin:$PATH
export PATH
Then I execute:
$ source $HOME/.bashrc
I've downloaded OpenCV's source code and moved to the platforms/linux folder as the official guide does:
$ cd ~/opencv/platforms/linux
$ mkdir -p build_hardfp
$ cd build_hardfp
Then in the "opencv/platforms/arm-gnueabi.toolchain.cmake" file, replaced these lines:
set(CMAKE_C_COMPILER arm-linux-gnueabi${FLOAT_ABI_SUFFIX}-gcc-${GCC_COMPILER_VERSION})
set(CMAKE_CXX_COMPILER arm-linux-gnueabi${FLOAT_ABI_SUFFIX}-g++-${GCC_COMPILER_VERSION})
by these:
set(CMAKE_C_COMPILER /usr/bin/arm-linux-gnueabihf-gcc)
set(CMAKE_CXX_COMPILER /usr/bin/arm-linux-gnueabihf-g++)
In order to use arm compiler instead of x86's.
Then I try to get cmake ready:
$ cmake -DBUILD_SHARED_LIBS=OFF -D BUILD_NEW_PYTHON_SUPPORT=NO -DCMAKE_TOOLCHAIN_FILE=../arm-gnueabi.toolchain.cmake ../../..
Cmake's output tells it will use arm cross compiler for ARM platform target, but it will not use Java bindings:
...
-- Platform:
-- Host: Linux 4.2.0-16-generic i686
-- Target: Linux 1 arm
-- CMake: 3.2.2
-- CMake generator: Unix Makefiles
-- CMake build tool: /usr/bin/make
-- Configuration: Release
...
C++ Compiler: /usr/bin/arm-linux-gnueabihf-g++ (ver 5.2.1)
...
-- OpenCV modules:
-- To be built: core flann imgproc highgui features2d calib3d ml video legacy objdetect photo gpu ocl nonfree contrib stitching superres ts videostab
-- Disabled: world
-- Disabled by dependency: -
-- Unavailable: androidcamera dynamicuda java python viz
So, I try to set cmake compile variables by myself without using cmake's toolchain file:
$ export CMAKE_C_COMPILER=/usr/bin/arm-linux-gnueabihf-gcc
$ export CMAKE_CXX_COMPILER=/usr/bin/arm-linux-gnueabihf-g++
$ cmake -DBUILD_SHARED_LIBS=OFF -D BUILD_NEW_PYTHON_SUPPORT=NO ../../..
Now cmake's output tells it will include Java support, but it won't use arm cross compiler:
...
-- Platform:
-- Host: Linux 4.2.0-16-generic i686
-- CMake: 3.2.2
-- CMake generator: Unix Makefiles
-- CMake build tool: /usr/bin/make
-- Configuration: Release
...
C++ Compiler: /usr/bin/c++ (ver 5.2.1)
...
-- OpenCV modules:
-- To be built: core flann imgproc highgui features2d calib3d ml video legacy objdetect photo gpu ocl nonfree contrib java stitching superres ts videostab
-- Disabled: world
-- Disabled by dependency: -
-- Unavailable: androidcamera dynamicuda python viz
Of course, if I execute make command with this latest cmake configuration, this is the ".so" file I get:
$ readelf -h lib/libopencv_java249.so | grep Machine
Machine: Intel 80386
where it should tell:
Machine: ARM
So, once again: I can compile OpenCV with Java bindings for x86 platform, or either OpenCV with NO Java bindings for ARM platform, but not both.
How should I do this?
Thank you!
UPDATE 1:
#Notlikethat I forgot to tell I had already tried that (i.e. use ARM jdk instead of x86). I did not mention it because I though I should be using x86.
However, I have tried it again:
I've downloaded ARM's jdk, set JAVA_HOME and PATH variables properly to point this new jdk and tried cmake command.
The result is the same, it lets me compile for ARM without Java bingings, or for x86 with Java bindings.
UPDATE 2:
I've added the following variables to the "arm-gnueabi.toolchain.cmake" file:
set(JAVA_HOME /usr/lib/jvm/jdk1.7.0_60_ARM)
set(JAVA_AWT_LIBRARY $JAVA_HOME/include/jawt.h)
set(JAVA_JVM_LIBRARY $JAVA_HOME/jre/lib/arm/jvm.cfg)
set(JAVA_INCLUDE_PATH $JAVA_HOME/include/jni.h)
set(JAVA_INCLUDE_PATH2 $JAVA_HOME/include/linux/jni_md.h)
set(JAVA_AWT_INCLUDE_PATH $JAVA_HOME/include/jawt.h)
Now if I execute:
$ cmake -DBUILD_SHARED_LIBS=OFF -D BUILD_NEW_PYTHON_SUPPORT=NO -DCMAKE_TOOLCHAIN_FILE=../arm-gnueabi.toolchain.cmake ../../..
the output shows that java module is still unavailable, but at least, one of its key dependencies is ok (JNI):
...
-- Java:
-- ant: NO
-- JNI: $JAVA_HOME/include/jni.h $JAVA_HOME/include/linux/jni_md.h $JAVA_HOME/include/jawt.h
-- Java tests: NO
...
I'm pretty sure the problem here is the fact that ant is not found, which I can't understand.
Ant is installed:
$ echo $PATH:/usr/lib/jvm/jdk1.7.0_60_ARM/bin:/opt/apache/ant/apache-ant-1.9.6/bin:...
I've retried by adding the following variables to the "arm-gnueabi.toolchain.cmake" file, without success:
set(ANT_HOME /opt/apache/ant/apache-ant-1.9.6)
set(JAVA_ANT $ANT_HOME/bin/ant)