Android NDK

Android NDK

by Abdun Nur Tomal

Step 1: Installing C/C++ Support on Eclipse

• Choose Eclipse Galileo to update
• Let the item preference tree load, and check
Eclipse C/C++ Development Tools in the
Programming Languages branch
• From -
http://www.eclipse.org/cdt/downloads.php

Step : Installing Cygwin
• Android is Linux based, and thus it is no
surprise that when build native code for it,
need some Unix tools.
• On Windows, NDK supports Cygwin 1.7.x and
above.
• It’s just a set of software that emulates Unix
environment on Windows
• get Cygwin, go to cygwin.com

“Install or update Cygwin now!”
• Cygwin’s setup.exe will download and run

• Choose Install from Internet, then click Next, then
choose the installation directory
(be sure to choose a directory path that contains no spaces in it) like –
C:/cygwin

Base packages installed,
Need the development packages
• After choose the mirror and click Next, Cygwin will download and
present to you the list of available packages:

• By default, only the base packages are installed. We, however, need
the development packages. Rather than picking the packages we
think we need

• We install the entire Devel branch.

• Click (once) on the word “Default” next to the root Devel node and
wait few seconds while the setup hangs.

• When it is back, you will see that “Default” changes to “Install” for
the Devel node, just like on the screenshot above.

• Click it once, let the Cygwin console start up and initialize:
• should see the same response that tells us that GNU Make is
present in our Unix environment that is emulated by Cygwin.

Android rich programming environment,
While the Android SDK provides a very
NDK
The Android NDK broadens the horizons and can speed up the delivery
of desired functionality by bringing in existing source code, some of
which may be proprietary and some of which may be open source
code.

The NDK includes all the components necessary to incorporate
functionality written in C into an Android application.

As of r5 of the NDK application,
• authors can write a significant portion of an application directly in
C, including user interface and event-handling capability.
As of r4b of the NDK application,
• The features enabling the image handling functionality
demonstrated here were introduced with the r4b version of the
NDK.

NDK Build
Two common uses of the NDK are
- to increase application performance and
Application performance improvements are available when
carefully crafted functions written in C are leveraged to perform
memory-based or computationally intensive operations.
- to leverage existing C code by porting it to Android.
The NDK is to port an existing body of C code written for
another platform, such as Linux.

The NDK contains a compiler and build scripts, allowing
- to focus on the C source files and
- leave the build magic to the NDK installation.

The NDK build process is easily incorporated into the Eclipse
development environment,

Step 3: Installing the Android NDK
• Android NDK itself and place it on our
filesystem.
• Can get NDK from the official Android site
• Be sure that there are no spaces in the path.
• Extract it to C:,
• so the path is C:android-ndk-r6.

Step 4: Making a Basic NDK App
• The general idea of using NDK in apps is to put
your native pieces of code into libraries that
you can then consume from the Java code.
• Use the New Android Project wizard
• However, an important thing to check , it is
spaces in the path again.

• In the project named ... Make a folder called jni in the root of the project (right-
click the project node, New – Folder).
• Create a file called Android.mk (New – File) within that folder with the following
contents:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
# Here we give our module name and source file(s)
LOCAL_MODULE := ndk_test
LOCAL_SRC_FILES := ndk_test.c
include $(BUILD_SHARED_LIBRARY)

The Android.mk file is important for the NDK build process to recognize your NDK modules. In our case we named our
module ndk_test and told the build tool that it consists of one source file named ndk_test.c. Let’s create it in the
same jni folder:

#include <string.h>
#include <jni.h>
jstring Java_com_mindtherobot_samples_ndkfoo_NdkFooActivity_invokeNativeFunction(JNIEnv* env, jobject javaThis)
{ return (*env)->NewStringUTF(env, "Hello from native code!"); }

• the C function – it matches the Java class name
• create a binary library from the C source that we
wrote,
• use a combination of Cygwin and Android NDK
tools.
• Launch the Cygwin console and use the cd
command to go directly to the folder where your
project is.
• the command line is:
/cygdrive/c/android-ndk-r4/ndk-build

• a successful run of the ndk-build tool will
create an .so file in a new folder called libs

• The .so file is the binary library that will be
included into the application .apk package
and will be available for the Java code of the
app to link to.

Ndk_testActivity class to use the NDK code:
package com.mindtherobot.samples.ndkfoo;

import android.app.Activity;
import android.app.AlertDialog;
import android.os.Bundle;

public class Ndk_testActivity extends Activity {
// load the library - name matches jni/Android.mk
static {
System.loadLibrary("ndkfoo");
}
// declare the native code function - must match ndk_test.c private native
String invokeNativeFunction();
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// this is where we call the native code
String hello = invokeNativeFunction();
new AlertDialog.Builder(this).setMessage(hello).show();
}
}

How to Build FFmpeg for Android
• Download Android NDK r5b
To download android ndk revision 5b and rev.6 use the following command:
http://dl.google.com/android/ndk/android-ndk-r5b-linux-x86.tar.bz2
http://dl.google.com/android/ndk/android-ndk-r6-linux-x86.tar.bz2

• Download Source Code for Ffmpeg
- http://ffmpeg.org/download.html
https://github.com/FFmpeg/FFmpeg
- The FFmpeg 0.8 “Love” need to downloaded.
http://ffmpeg.zeranoe.com/builds/

• Build FFmpeg
(The script is based on RockPlayer build script)
RockPlayer open source component: http://rockplayer.freecoder.org/tech.html
http://roman10.net/src/build_android_r5b.txt
http://roman10.net/src/build_android_r6.txt

• The Output of the Build

All about JNI
• Java Native Interface (JNI)
• The JNI is a part of the Java platform,
programmers can address interoperability
issues once, and expect their solution to work
with all implementations of the Java platform.
“Applications written in the Java programming
language as well as in native (C, C++, etc.)
programming languages.”

Activity Seems
clarify the exact scope of the programming environments for these
languages.
• Java applications are written in the Java programming
language, and compiled into a machine-independent binary class
format.
• The Java API consists of a set of predefined classes.
• Any implementation of the Java platform is guaranteed to support
the Java programming language, virtual machine, and API.
• The term host environment represents the host operating system, a
set of native libraries, and the CPU instruction set.
• Native applications are written in native programming languages
such as C and C++, compiled into host-specific binary code, and
linked with native libraries.
• We know, Native applications and native libraries are typically
dependent on a particular host environment.
• A C application built for one operating system, for example, typically
does not work on other operating systems.

Java Platform do
• Java platforms are commonly deployed on top of
a host environment.
For example, the Java Runtime Environment (JRE) is
a Sun product that supports the Java platform on
existing operating systems such as Solaris and
Windows.

• The Java platform offers a set of features that
applications can rely on independent of the
underlying host environment.

Role of the JNI
• The JNI is a powerful feature that allows you to take advantage of the Java
platform, but still utilize code written in other languages. As a part of the Java
virtual machine implementation, the JNI is a two-way interface that allows Java
applications to invoke native code and vice versa. Figure -

JNI - Two-way interface
• As a two-way interface, the JNI can support two types of native
code:
- Native libraries and
- Native applications.
- Applications call native methods in the same way that they call
methods implemented in the Java programming language.
- An invocation interface :
Native applications can link with a native library that implements
the Java virtual machine, and then ..
Use the invocation interface to execute software components
written in the Java programming language.
For example, a web browser written in C can execute downloaded
applets in an embedded Java virtual machine implemention.

JNI - Risks
• It risks losing two benefits of the Java platform
- First,
Java applications that depend on the JNI can no longer readily run on multiple host
environments.
It will be necessary to recompile the part of the application written in native programming
languages.
- Second,
The Java programming language is type-safe and secure, native languages such as C or C++
are not.
while this point may be for those OS Development which might have independent hardware
licensing issues.

When to Use the JNI ?
A number of alternative approaches also allow Java applications to interoperate with code
written in other languages. For example:
• A Java application may communicate with a native application through a TCP/IP connection
or through other inter-process communication (IPC) mechanisms.
• A Java application may connect to a legacy database through the JDBCTM API.
• A Java application may take advantage of distributed object technologies such as the Java IDL
API.

When the JNI becomes useful ?
The following scenarios:
• Targeted Java API might not support certain host-dependent
features needed by an application.
• May want to access an existing native library and are not willing to
pay for the overhead of copying and transmitting data across
different processes.
• Loading a native library into the existing process hosting the
application requires less system resources than starting a new
process and loading the library into that process.
• If a 3D-intensive application spends most of its time in graphics
rendering, you may find it necessary to write the core portion of a
graphics library in assembly code to achieve maximum
performance. Like, Games, Ex-H/W ….
• Have role on the JDK
- The JNI was first supported in JDK release 1.1. Internally.
- Java 'jdk' is the 'Java Development Kit' and it allows you to compile
Java programs.

Develop JNI libraries for Android phones
The steps that you have to take to develop JNI libraries for Android phones are simple
in principle.

They are outlined below.
• Install the JNI/NDK package from Google
• Create your Android project
• Make a JNI folder in your Android project root directory (called 'jni')
• Put your JNI sources in the 'jni' folder
• Create an 'Android.mk' file, and place it in the 'jni' folder
• Optionally create an 'Application.mk' file, and place it in the 'jni' folder
• Open a command line terminal and navigate to the root directory of your Android
project.
• Execute 'ndk-build', (if it's in your PATH variable) or execute
'/path/to/command/ndk-build'
• The 'ndk-build' command creates the binary for your library and puts it in the
proper folder.
• Switch to Eclipse, Refresh the 'Project Explorer View' (F5)
• Rebuild the project
• Run your project testing your JNI library.

Android.mk files
We'll leave most of the file as it is.
• LOCAL_PATH - this line should be left as it is since your source file
('example.c') is in the same directory as the 'Android.mk' file.
• include $(CLEAR_VARS) - this line should be left as it is. It is
required.
• LOCAL_MODULE - this line should be changed to match your
module name. For this tutorial we'll change it to 'example'. This
name should not have any spaces in it as it will be made into the
actual library's name ('libexample.so' for us).
• LOCAL_CFLAGS - This line can be left as it is. It is for compiler flags.
• LOCAL_SRC_FILES - this line should be changed to 'example.c' since
that's our source file.
• LOCAL_LDLIBS - leave this the same.
• include $(BUILD_SHARED_LIBRARY) - leave this the same.

How to configure a script for making a
library and an Android.mk file
• Configure script to generate the
– config.h and config.mak files.

– http://code.google.com/p/awesomeguy/wiki/JNITutor
ial#Overview
– CV Ready + Cygwin Devel Branch + NDK set
– YA cam recorder + ffmpeg test project for making
ffmpeg library + Color Conversion yuv2rgb
– halfninja-android-ffmpeg-x264-04b62f2 need ffmpeg
library
– Test the project + ffmpeg tutorial search

Android NDK

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