Develop Reference

How do I build the arcore camera_utility shared library in NDK-BUILD?

I'm trying to build the 'arcore camera utility' library in NDK_BUILD, here: https://github.com/google-ar/arcore-unity-sdk/tree/master/Assets/GoogleARCore/Examples/ComputerVision/Plugins/src
Using this guide: https://yeephycho.github.io/2016/10/20/How-to-Use-NDK-to-Build-A-Shared-Android_Native-Library/ I was at least able to get it to compile in a libarcore_camera_utility.so file. Not only that but it was actually recognized by my app on the phone and instead of getting a DLL missing error I got the error: "EntryPointNotFoundException: Unable to find an entry point named 'TextureReader_create' in 'arcore_camera_utility'." which means it at least found the file, now.
The filesize of the .so is only 6k so it seems like I'm not compiling it correctly as the already working 32bit version that comes with the package is 100k, based on this question it seems like I'm leaving something out?: Entry point not found, Android .so file
My Android.mk file is:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := arcore_camera_utility_shared
LOCAL_C_INCLUDES += \
LOCAL_SRC_FILES := camera_utility.cc gl_utility.cc texture_reader.cc
include $(BUILD_STATIC_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := arcore_camera_utility
LOCAL_WHOLE_STATIC_LIBRARIES := arcore_camera_utility_shared
include $(BUILD_SHARED_LIBRARY)
And my Application.mk file contains:
APP_ABI := arm64-v8a
APP_PLATFORM := android-24
APP_STL := c++_static
APP_BUILD_SCRIPT := ./jni/Android.mk
Am I building it in such a way as to leave the code out?

To compile arcore_camera_utility for the arm 64bit target-
1.) Create a new directory called 'arcorelibrary', then a subdirectory called 'jni'
2.) Download this zip: https://github.com/google-ar/arcore-unity-sdk/blob/master/Assets/GoogleARCore/Examples/ComputerVision/Plugins/src/arcore_camera_utility.zip
3.) get the three .cc files and the three .h files and place them in the jni directory
4.) Create a file called 'Android.mk' and place it in the jni directory, with the following contents:
LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE:= arcore_camera_utility_static
LOCAL_SRC_FILES:= camera_utility.cc gl_utility.cc texture_reader.cc
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)
LOCAL_EXPORT_LDLIBS := -llog -landroid -lEGL -lGLESv2 -lGLESv3
include $(BUILD_STATIC_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := arcore_camera_utility
LOCAL_WHOLE_STATIC_LIBRARIES := arcore_camera_utility_static
include $(BUILD_SHARED_LIBRARY)
5.) Create a file called 'Application.mk' and place it in the jni directory, with the following contents:
APP_ABI := arm64-v8a
APP_PLATFORM := android-24
APP_STL := c++_static
APP_BUILD_SCRIPT := ./jni/Android.mk
6.) Download Android NDK and unzip somewhere (The version you need depends on which Unity version you're using) https://developer.android.com/ndk/downloads/older_releases.html
7.) Open a terminal or powershell, go to the root directory (arcorelibrary) of your project
8.) Create a path to where ever you unzipped Android NDK (Powershell example):
$env:Path += ";C:\[where-ever-you-unzipped]\android-ndk-r13b-windows-x86_64\android-ndk-r13b"
9.) Run:
ndk-build.cmd

Cannot import libpng, libjpeg in ndk android

I forked, Ucrop library for cropping, and made some changes. Now i have to build the ndk to make the changes. But am keep getting this error:
Android NDK: jni/Android.mk: Cannot find module with tag 'libpng' in import path
Android NDK: Are you sure your NDK_MODULE_PATH variable is properly defined ?
Android NDK: The following directories were searched:
Android NDK: jni/Android.mk:15: *** Android NDK: Aborting. . Stop.
The project uses Cimg library.
This is my Android.mk file:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := ucrop
LOCAL_SRC_FILES := uCrop.cpp
LOCAL_LDLIBS := -landroid -llog -lz
LOCAL_STATIC_LIBRARIES := libpng libjpeg_static
include $(BUILD_SHARED_LIBRARY)
$(call import-module,libpng)
$(call import-module,libjpeg)
I tried all solutions that given online. But nothing worked. I tried "Adding libpng in android ndk project" and many answers.

Atlast I made it work. It was hard because I was a beginner in NDK. But i will post how i did it in here, since it may help other beginners.
First I download libpng and libjpeg, and saved it under Android/Sdk/ndk-bundle/sources. I saved those under names, libpng and libjpeg respectively.
Then modify Android.mk as below,
LOCAL_PATH := $(call my-dir)
LOCAL_P := /usr/lib/
include $(CLEAR_VARS)
LOCAL_MODULE := ucrop
LOCAL_SRC_FILES := uCrop.cpp
LOCAL_LDLIBS := -landroid -llog -lz
LOCAL_STATIC_LIBRARIES := libpng libjpeg9
include $(BUILD_SHARED_LIBRARY)
$(call import-module,libpng/jni)
$(call import-module,libjpeg/libjpeg9)
Then set environment path NDK_MODULE_PATH as below,
export NDK_BUILD_PATH=/home/jerin/Android/Sdk/ndk-bundle/sources
This is important since, during ndk build, it looks for the libraries in this path.
You can compile ndk-build during gradle build by following [this][1].
Right-click on the module you would like to link to your native library, such as the app module, and select Link C++ Project with Gradle from the menu. Then select ndk-build, and give path to Android.mk

Specify directory for external C++ library +NDK +Android studio

I'm new to this NDK build and I'm having trouble with running this Buildbox project in android studio.
After linking C++ to Gradle using ndk-build and syncing, it is giving this error.
Android NDK: C:\AndroidApps\app\app\src\main\jni\Android.mk: Cannot find module with tag 'box2D' in import path
Android NDK: Are you sure your NDK_MODULE_PATH variable is properly defined?
Android NDK: The following directories were searched:
Android NDK:
process_begin: CreateProcess(NULL, "", ...) failed.
I can see reference for cocos2dx in the java and resources subfolders.
I'm not sure if I have to download box2D,core,cocos2dx library .
What changes do I have to make to the android.mk file so that the errors are gone?
Here is the android.mk file
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := player_shared
LOCAL_MODULE_FILENAME := libplayer
LOCAL_SRC_FILES := main.cpp
LOCAL_WHOLE_STATIC_LIBRARIES := core_static cocos2dx_static box2d_static
GOOGLE_PLAY_STORE := true
include $(BUILD_SHARED_LIBRARY)
$(call import-add-path, $(LOCAL_PATH)/platform/third_party/android/prebuilt)
$(call import-module, box2D)
$(call import-module, core)
$(call import-module, cocos2dx)

NDK does not download imported modules for you. I am not sure if there are plans to add such feature (parallel to XCode pods) in the future.
You will find detailed description of import-module here, but basically you can set NDK_MODULE_PATH in your Application.mk file, with ; separators on Windows, but using straight / in paths instead of Windows native backsashes, e.g. C:/ext), and then
$(call import-module, box2D)
will be equivalent to
include C:/ext/box2D/Android.mk

Cannot run ndk-build on Terminal

I am new to using NDK platform and I get the following error on running ndk-build in the terminal:
aditya#aditya-Vostro1510:~/workspace/Fibonacci$ ~/android-ndk-r9/ndk-build
Android NDK: WARNING: APP_PLATFORM android-18
is larger than android:minSdkVersion8 in ./AndroidManifest.xml
Android NDK: Your APP_BUILD_SCRIPT points to an unknown file: ./jni/Android.mk
/home/aditya/android-ndk-r9/build/core/add-application.mk:176: *** Android NDK: Aborting... . Stop.
I didnt make an application.mk file as I read it was optional and the video tutorial I refered did not include it too.
android.mk contains foll code:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_SRC_FILES := com_Native_fibonacci_fiblib.c
LOCAL_MODULE := com_Native_fibonacci_fiblib
include $(BUILD_SHARED_LIBRARY)
I tried searching for help on forums but failed.Please give me a detailed solution for this.

Eclipse can't include opencv2 header files

I've created an Android Application Project in Eclipse Juno, and after I've added native support to this project (Android Tools -> Add Native Support). So Eclipse has added in the project automatically a jni directory, within which a .cpp file and the file Android.mk.
Then I've build the project, without errors.
In order to use opencv for android libraries (2.4.5), I've added the path to the 'include' directory of these libraries in the project (Properties -> C/C++ General -> Path And Symbols -> Include Diretories). I've also set in the Eclipse Preferences -> NDK the correct path to the ndk directory in my pc, to make possible to execute ndk-build when I build the projects.
But, if i try to include in the .cpp file:
#include <opencv2/opencv.hpp>
The console show me this result:
12:24:25 **** Build of configuration Default for project ProvaVideoCapture ****
"C:\\Users\\Micaela\\Desktop\\Android\\android-ndk-r8e\\ndk-build.cmd" all
"Compile++ thumb : jniVideoCapture <= jniVideoCapture.cpp
jni/jniVideoCapture.cpp:4:30: fatal error: opencv2/opencv.hpp: No such file or directory
compilation terminated.
make: *** [obj/local/armeabi-v7a/objs/jniVideoCapture/jniVideoCapture.o] Error 1
12:24:26 Build Finished (took 282ms)
My Android.mk file is:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := jniVideoCapture
LOCAL_SRC_FILES := jniVideoCapture.cpp
include $(BUILD_SHARED_LIBRARY)
The Application.mk file that I've added manually (it has not been automatically added by Eclipse) is:
APP_ABI := all
APP_STL := gnustl_static
APP_CPPFLAGS := -frtti -fexceptions
APP_PLATFORM := android-9
I don't know how to solve this problem, or what I've done wrong.
Could you help me?

Add path like below to your Android.mk file and check
include E:/OpenCV-2.3.1/share/OpenCV/OpenCV.mk
Sample Android.mk for reference
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
OPENCV_LIB_TYPE:=STATIC
OPENCV_INSTALL_MODULES:=on
include E:/OpenCV-2.3.1/share/OpenCV/OpenCV.mk
include $(OPENCV_MK_PATH)
LOCAL_MODULE := firstcv
LOCAL_SRC_FILES := first.cpp
LOCAL_LDLIBS += -llog -ldl
include $(BUILD_SHARED_LIBRARY)