Develop Reference

Build OpenCV for Android with CMake's ExternalProject_Add

I am creating an Android library that uses OpenCV via NDK. It doesn't require any Java parts of OpenCV, native parts only, so I decided not to use OpenCV for Android to reduce the size of the OpenCV code the library needs.
Now I need to download and build the native (C++) part of OpenCV using CMake so that the library won't require its users to download and install OpenCV on their own.
Currently my module's build.gradle contains this:
externalNativeBuild {
cmake {
cppFlags '-std=c++11 -frtti -fexceptions'
arguments '-DANDROID_ARM_NEON=TRUE'
}
}
And my CMakeLists.txt is:
cmake_minimum_required(VERSION 3.18.1)
project("mylib")
set(OPENCV_INSTALL_DIR ${CMAKE_BINARY_DIR}/opencv-install)
include(ExternalProject)
ExternalProject_Add(opencv
GIT_REPOSITORY https://github.com/opencv/opencv.git
GIT_TAG 4.5.5
UPDATE_DISCONNECTED TRUE
CMAKE_ARGS
<OpenCV arguments I need>
-DCMAKE_INSTALL_PREFIX=${OPENCV_INSTALL_DIR}
)
include_directories(${OPENCV_INSTALL_DIR}/include)
link_directories(${OPENCV_INSTALL_DIR}/lib)
set(OPENCV_LIBRARIES <OpenCV modules I use>)
add_library(mylib SHARED mylib.cpp)
add_dependencies(mylib opencv)
find_library(log-lib log)
target_link_libraries(mylib ${log-lib} ${OPENCV_LIBRARIES})
I am using Android Studio. When I try to build the library, the downloading process goes fine, but at the configure step I get the following error:
FAILED: opencv-prefix/src/opencv-stamp/opencv-configure
cmd.exe /C "cd /D <my lib module path>\.cxx\Debug\612145b5\x86_64\opencv-prefix\src\opencv-build && <my Android SDK path>\cmake\3.18.1\bin\cmake.exe -DBUILD_TESTS=OFF -DBUILD_PERF_TESTS=OFF -DBUILD_EXAMPLES=OFF -DBUILD_opencv_apps=OFF -DBUILD_JAVA=OFF -DBUILD_FAT_JAVA_LIB=OFF -DBUILD_opencv_python2=OFF -DBUILD_opencv_python3=OFF -DWITH_GTK=OFF -DWITH_WIN32UI=OFF -DWITH_FFMPEG=OFF -DWITH_V4L=OFF -DCPU_BASELINE=NEON -DCMAKE_INSTALL_PREFIX=<my lib module path>/.cxx/Debug/612145b5/x86_64/opencv-install -GNinja <my lib module path>/.cxx/Debug/612145b5/x86_64/opencv-prefix/src/opencv && <my Android SDK path>\cmake\3.18.1\bin\cmake.exe -E touch <my lib module path>/.cxx/Debug/612145b5/x86_64/opencv-prefix/src/opencv-stamp/opencv-configure"
CMake Error: CMake was unable to find a build program corresponding to "Ninja". CMAKE_MAKE_PROGRAM is not set. You probably need to select a different build tool.
CMake Error: CMAKE_CXX_COMPILER not set, after EnableLanguage
CMake Error: CMAKE_C_COMPILER not set, after EnableLanguage
As I see, CMake cannot find the following components:
Ninja
C++ compiler
C compiler
I can get rid of the first error, if I add ninja's path from NDK to the PATH variable, I don't think thats how it should be done though. Neither do I want to pass CMAKE_CXX_COMPILER and CMAKE_C_COMPILER to CMake manually, as it seems like it should be done automatically by Android Studio.
So, how can I fix this?

CMake/Android error: "not able to compile a simple test program"

I am trying to compile a CMake project for android.
I use QtCreator to create and compile the project. Using QMake works fine, but CMake projects don't work.
CMake Project parsing failed.
Running "C:\Android\android-sdk\cmake\3.10.2.4988404\bin\cmake.exe -E server "--pipe=\\.\pipe\{78eb9a25-fbdf-4ac7-b840-8cfe89cbd883}" --experimental" in C:\Users\Thorsten\AppData\Local\Temp\QtCreator-Zmienl\qtc-cmake-KUabkXqG.
Starting to parse CMake project, using: "-DCMAKE_CXX_COMPILER:STRING=C:/Android/android-sdk/ndk-bundle/toolchains/llvm/prebuilt/windows-x86_64/bin/clang++.exe", "-DCMAKE_C_COMPILER:STRING=C:/Android/android-sdk/ndk-bundle/toolchains/llvm/prebuilt/windows-x86_64/bin/clang.exe", "-DCMAKE_PREFIX_PATH:STRING=C:/Qt/5.13.0/android_x86_64", "-DQT_QMAKE_EXECUTABLE:STRING=C:/Qt/5.13.0/android_x86_64/bin/qmake.exe".
The CXX compiler identification is Clang 8.0.2
Check for working CXX compiler: C:/Android/android-sdk/ndk-bundle/toolchains/llvm/prebuilt/windows-x86_64/bin/clang++.exe
Check for working CXX compiler: C:/Android/android-sdk/ndk-bundle/toolchains/llvm/prebuilt/windows-x86_64/bin/clang++.exe -- broken
CMake Error at C:/Android/android-sdk/cmake/3.10.2.4988404/share/cmake-3.10/Modules/CMakeTestCXXCompiler.cmake:45 (message):
The C++ compiler
"C:/Android/android-sdk/ndk-bundle/toolchains/llvm/prebuilt/windows-x86_64/bin/clang++.exe"
is not able to compile a simple test program.
It fails with the following output:
Change Dir: C:/Users/Thorsten/AppData/Local/Temp/QtCreator-Zmienl/qtc-cmake-KUabkXqG/CMakeFiles/CMakeTmp
Run Build Command:"C:/Android/android-sdk/cmake/3.10.2.4988404/bin/ninja.exe" "cmTC_622f7"
[1/2] Building CXX object CMakeFiles/cmTC_622f7.dir/testCXXCompiler.cxx.obj
[2/2] Linking CXX executable cmTC_622f7.exe
FAILED: cmTC_622f7.exe
cmd.exe /C "cd . && C:\Android\android-sdk\ndk-bundle\toolchains\llvm\prebuilt\windows-x86_64\bin\clang++.exe CMakeFiles/cmTC_622f7.dir/testCXXCompiler.cxx.obj -o cmTC_622f7.exe -Wl,--out-implib,libcmTC_622f7.dll.a -Wl,--major-image-version,0,--minor-image-version,0 -lkernel32 -luser32 -lgdi32 -lwinspool -lshell32 -lole32 -loleaut32 -luuid -lcomdlg32 -ladvapi32 && cd ."
clang++.exe: error: unable to execute command: program not executable
clang++.exe: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.
CMake will not be able to correctly generate this project.
Call Stack (most recent call first):
CMakeLists.txt:8 (project)
Configuring incomplete, errors occurred!
See also "C:/Users/Thorsten/AppData/Local/Temp/QtCreator-Zmienl/qtc-cmake-KUabkXqG/CMakeFiles/CMakeOutput.log".
See also "C:/Users/Thorsten/AppData/Local/Temp/QtCreator-Zmienl/qtc-cmake-KUabkXqG/CMakeFiles/CMakeError.log".
CMake Project parsing failed.
I found several posts about this, but most of them were not answered or simply not useful. I found this helpful, so I added
SET (CMAKE_C_COMPILER_WORKS 1)
SET (CMAKE_CXX_COMPILER_WORKS 1)
before project(). But now I get
CMake Error in CMakeLists.txt:
No known features for CXX compiler
"Clang"
version 8.0.2.
CMake Project parsing failed.
So far I haven't found something useful for that.
I hope I can get some more help this way.
ps: I recently reinstalled my os (Windows 10), so if I forgot to update something it's not older than two month. I let QtCreator, Visual Studio and Android Studio do the installation of the toolchains.
pps: The project is a new project created by QtCreator

Fail to create new Android NDK project

I want to learn how to write code in Android NDK.
I open the 'android studio guide' and on the 'create new ndk project' I follow the instruction.
I just create new project and add support for C++ code and that's it .. all the IDE code is in red and nothing can be compile.
Can't find any problem and I don't know what to do.
Tried to sync by clicking 'Try again' in first - and still fail.
The error message is:
CMake Error at
C:/Users/AppData/Local/Android/sdk/ndk-bundle/build/cmake/android.toolchain.cmake:40
(cmake_minimum_required): CMake 3.6.0 or higher is required. You
are running version 3.4.1 Call Stack (most recent call first):
C:/Users/AppData/Local/Android/sdk/cmake/share/cmake-3.4/Modules/CMakeDetermineSystem.cmake:98
(include) CMakeLists.txt CMake Error: CMAKE_C_COMPILER not set,
after EnableLanguage CMake Error: CMAKE_CXX_COMPILER not set, after
EnableLanguage
-- Configuring incomplete, errors occurred! Build command failed. Error while executing process
C:\Users\AppData\Local\Android\sdk\cmake\bin\cmake.exe with arguments
{-HC:\WORKSPACE\Android\Practice\NDK\Practice_001\app
-BC:\WORKSPACE\Android\Practice\NDK\Practice_001\app.externalNativeBuild\cmake\debug\armeabi
-GAndroid Gradle - Ninja -DANDROID_ABI=armeabi -DANDROID_NDK=C:\Users\Rn\AppData\Local\Android\sdk\ndk-bundle -DCMAKE_LIBRARY_OUTPUT_DIRECTORY=C:\WORKSPACE\Android\Practice\NDK\Practice_001\app\build\intermediates\cmake\debug\obj\armeabi
-DCMAKE_BUILD_TYPE=Debug -DCMAKE_MAKE_PROGRAM=C:\Users\AppData\Local\Android\sdk\cmake\bin\ninja.exe
-DCMAKE_TOOLCHAIN_FILE=C:\Users\AppData\Local\Android\sdk\ndk-bundle\build\cmake\android.toolchain.cmake
-DANDROID_PLATFORM=android-24 -DCMAKE_CXX_FLAGS=-frtti -fexceptions} CMake Error at
C:/Users/AppData/Local/Android/sdk/ndk-bundle/build/cmake/android.toolchain.cmake:40
(cmake_minimum_required): CMake 3.6.0 or higher is required. You
are running version 3.4.1 Call Stack (most recent call first):
C:/Users/AppData/Local/Android/sdk/cmake/share/cmake-3.4/Modules/CMakeDetermineSystem.cmake:98
(include) CMakeLists.txt CMake Error: CMAKE_C_COMPILER not set,
after EnableLanguage CMake Error: CMAKE_CXX_COMPILER not set, after
EnableLanguage
-- Configuring incomplete, errors occurred!
Thanks for any help.

Click on the "Try again" in yellow banner. If you got the error still probably problem is with you do not have necessary library packages in your build.gradle file. Check if you have added necessary Support Library Packages in your build.gradle file. If doesn't then add it and "rebuild" your project.

Your error message is:
CMake 3.6.0 or higher is required. You are running version 3.4.1
I do not know whether you have your own CMake installation or you are attempting to use one that comes from Android Studio. My guess is that you have your own CMake installation. If so, upgrade it to 3.6.0 or higher.

Android studio error while creating project with NDK support

I tried to create simple android application with NDK support. I followed https://developer.android.com/studio/projects/add-native-code.html#new-project while creating project. After creating project it gives me following error:
External Native Build Issues
Build command failed.
Error while executing 'C:\Users\Nilesh.Kashid\AppData\Local\Android\Sdk\cmake\3.6.3155560\bin\cmake.exe' with arguments {-HD:\AndroidNDKExample\app -BD:\AndroidNDKExample\app\.externalNativeBuild\cmake\release\armeabi -GAndroid Gradle - Ninja -DANDROID_ABI=armeabi -DANDROID_NDK=C:\Users\Nilesh.Kashid\AppData\Local\Android\Sdk\ndk-bundle -DCMAKE_LIBRARY_OUTPUT_DIRECTORY=D:\AndroidNDKExample\app\build\intermediates\cmake\release\obj\armeabi -DCMAKE_BUILD_TYPE=Release -DCMAKE_MAKE_PROGRAM=C:\Users\Nilesh.Kashid\AppData\Local\Android\Sdk\cmake\3.6.3155560\bin\ninja.exe -DCMAKE_TOOLCHAIN_FILE=C:\Users\Nilesh.Kashid\AppData\Local\Android\Sdk\cmake\3.6.3155560\android.toolchain.cmake -DANDROID_NATIVE_API_LEVEL=19 -DCMAKE_CXX_FLAGS=-frtti -fexceptions}
-- Configuring incomplete, errors occurred!
CMake Error at C:/Users/Nilesh.Kashid/AppData/Local/Android/sdk/cmake/3.6.3155560/android.toolchain.cmake:351 (message):
Failed to parse Android NDK revision:
C:/Users/Nilesh.Kashid/AppData/Local/Android/Sdk/ndk-bundle/source.properties.
Call Stack (most recent call first):
C:/Users/Nilesh.Kashid/AppData/Local/Android/sdk/cmake/3.6.3155560/share/cmake-3.6/Modules/CMakeDetermineSystem.cmake:98 (include)
CMakeLists.txt
CMake Error: CMAKE_C_COMPILER not set, after EnableLanguage
CMake Error: CMAKE_CXX_COMPILER not set, after EnableLanguage
Error:executing external native build for cmake D:\AndroidNDKExample\app\CMakeLists.txt
Build command failed.
Error while executing 'C:\Users\Nilesh.Kashid\AppData\Local\Android\Sdk\cmake\3.6.3155560\bin\cmake.exe' with arguments {-HD:\AndroidNDKExample\app -BD:\AndroidNDKExample\app\.externalNativeBuild\cmake\debug\armeabi -GAndroid Gradle - Ninja -DANDROID_ABI=armeabi -DANDROID_NDK=C:\Users\Nilesh.Kashid\AppData\Local\Android\Sdk\ndk-bundle -DCMAKE_LIBRARY_OUTPUT_DIRECTORY=D:\AndroidNDKExample\app\build\intermediates\cmake\debug\obj\armeabi -DCMAKE_BUILD_TYPE=Debug -DCMAKE_MAKE_PROGRAM=C:\Users\Nilesh.Kashid\AppData\Local\Android\Sdk\cmake\3.6.3155560\bin\ninja.exe -DCMAKE_TOOLCHAIN_FILE=C:\Users\Nilesh.Kashid\AppData\Local\Android\Sdk\cmake\3.6.3155560\android.toolchain.cmake -DANDROID_NATIVE_API_LEVEL=19 -DCMAKE_CXX_FLAGS=-frtti -fexceptions}
-- Configuring incomplete, errors occurred!
CMake Error at C:/Users/Nilesh.Kashid/AppData/Local/Android/sdk/cmake/3.6.3155560/android.toolchain.cmake:351 (message):
Failed to parse Android NDK revision:
C:/Users/Nilesh.Kashid/AppData/Local/Android/Sdk/ndk-bundle/source.properties.
Call Stack (most recent call first):
C:/Users/Nilesh.Kashid/AppData/Local/Android/sdk/cmake/3.6.3155560/share/cmake-3.6/Modules/CMakeDetermineSystem.cmake:98 (include)
CMakeLists.txt
CMake Error: CMAKE_C_COMPILER not set, after EnableLanguage
CMake Error: CMAKE_CXX_COMPILER not set, after EnableLanguage
Error:executing external native build for cmake D:\AndroidNDKExample\app\CMakeLists.txt
I have downloaded CMake and LLDB android I am using Android Studio 2.2.3 version.

I had the same problem. This problem occurs in older versions of ndk.
Failed to parse Android NDK revision:
The problem was resolved after updating ndk.
The current ndk version is 13.1.3345770.
Reference :
https://developer.android.com/ndk/guides/index.html

cmake fails with android ndk

I am trying to build something using the Android NdK standalone toolchain. However, I am running into these errors.
CMake Warning at cmake/android.toolchain.cmake:387 (message):
Using value of obsolete variable ANDROID_NDK_TOOLCHAIN_ROOT as initial
value for ANDROID_STANDALONE_TOOLCHAIN. Please note, that
ANDROID_NDK_TOOLCHAIN_ROOT can be completely removed in future versions of
the toolchain.
Call Stack (most recent call first):
cmake/android.toolchain.cmake:476 (__INIT_VARIABLE)
/usr/local/Cellar/cmake/2.8.10.2/share/cmake/Modules/CMakeDetermineSystem.cmake:86 (include)
CMakeLists.txt:16 (PROJECT)
CMake Error at cmake/android.toolchain.cmake:412 (FILE):
file STRINGS file
"/Users/vgokhale/Desktop/android-ndk-r8e/sysroot/usr/include/android/api-level.h"
cannot be read.
Call Stack (most recent call first):
cmake/android.toolchain.cmake:548 (__DETECT_NATIVE_API_LEVEL)
/usr/local/Cellar/cmake/2.8.10.2/share/cmake/Modules/CMakeDetermineSystem.cmake:86 (include)
CMakeLists.txt:16 (PROJECT)
CMake Error: Error required internal CMake variable not set, cmake may be not be built correctly.
Missing variable is:
CMAKE_C_COMPILER_ENV_VAR
CMake Error: Error required internal CMake variable not set, cmake may be not be built correctly.
Missing variable is:
CMAKE_C_COMPILER
CMake Error: Could not find cmake module file:/Users/vgokhale/Desktop/torch-android/src/build/CMakeFiles/2.8.10.2/CMakeCCompiler.cmake
CMake Error: Error required internal CMake variable not set, cmake may be not be built correctly.
Missing variable is:
CMAKE_CXX_COMPILER_ENV_VAR
CMake Error: Error required internal CMake variable not set, cmake may be not be built correctly.
Missing variable is:
CMAKE_CXX_COMPILER
CMake Error: Could not find cmake module file:/Users/vgokhale/Desktop/torch-android/src/build/CMakeFiles/2.8.10.2/CMakeCXXCompiler.cmake
CMake Error: CMAKE_C_COMPILER not set, after EnableLanguage
CMake Error: CMAKE_CXX_COMPILER not set, after EnableLanguage
-- Configuring incomplete, errors occurred!
make: *** No rule to make target `install'. Stop.
There are two sets of errors. I have no idea where to begin with the first set. The android.toolchain.cmake file looks into sysroot by default but android is not installed there neither does Google require me to install it there.
Regarding the CMAKE variables, I found that most solutions involve installing Developer Tools, which I already have. I tried manually setting the CXX and CC variables but that did not help.
Any ideas as to where to start?
Thank you.

Ok, I'll do a bit of guesswork here, but I think you're using http://code.google.com/p/android-cmake/ and you're calling it with ANDROID_STANDALONE_TOOLCHAIN while providing it the path to your NDK. If I'm right, that's the problem.
You should either call it with ANDROID_NDK and provide the path to your NDK.
The android-cmake documentation suggests that this is the way to go.
or
Keep calling it with ANDROID_STANDALONE_TOOLCHAIN, but providing it the path to an installed toochain (something created with make-standalone-toolchain.sh)
If you want to go this way, you can find information about creating standalone toolchains in docs/STANDALONE-TOOLCHAIN.html in your installed NDK.