Let’s start with CMake, it allows us to create projects out of source codes and build them using our favorite IDEs or make/build systems. What is the purpose of each one of the prerequisites? Here is a question that is usually skipped in tutorials, so for those of you who are interested in understanding the whole process, we’re going to ask it and try to provide some clear but brief answers for it. You can get individual Android NDK revisions from here. Important note for OpenCV version 4.0.1 prerequisites: You’ll need Android NDK Revision 16b for properly building this particular version of OpenCV and you might face issues if you use a version of NDK higher that the one we mentioned. Use SDK manager in Android Studio to get the latest Android SDK and NDK.Android Studio (It’s available here, download the latest version available.).Get MinGW (If you’re a Qt fan and you want to use it for building Android app, Qt installer includes MinGW by default so you can use that one, otherwise refer to the official MinGW website to get it).CMake (Get the latest version from CMake website, I’ll use CMake 3.13.3).OpenCV 4.x source codes of course (You can get them here in a zip file if you choose sources instead of pre-built binaries or you can clone then from here, I’ll use OpenCV 4.0.1 just for reference).You just need to convert the steps with MinGW to default make command in Linux/Unix.įirst things first, the prerequisites for building OpenCV 4.x for Android are: Please note that this tutorial is written with Windows users in mind but you should be able to build with “almost” the same steps under Linux and macOS as well. So without without further ado, here we go. That post was based on OpenCV 3.3 which is considered out-of-date these days, especially with OpenCV 4 out in the market (OpenCV 4.0.1 at the time of writing this article), so I decided to write a new tutorial to address some of the differences. Since you’ve ended up reading this post, there’s a good chance that you already know why you might need to do this, but if you don’t, you can check out my similar post from a couple of years ago for some answers on this. Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.For a number of different reasons, you might want/need to build OpenCV from scratch instead of using the pre-built and official libraries provided by OpenCV. Want to build and generate the database as a side-effect.Ĭontent and code samples on this page are subject to the licenses described in the Content License. Without building your code, or ndk-build GEN_COMPILE_COMMANDS_DB=true if you You can either use ndk-build compile_commands.json to generate the database In NDK r18 and newer, ndk-build can generate a Own copy of GNU Make and will use that unless you've set the $GNUMAKEĮnvironment variable to point to an unsuitable make. You need GNU Make 4 to use ndk-build or the NDK in general. The syntax on the command line is, for example: `APP_OPTIM=debug` in `Application.mk`, and compiles with `-O0`.įor more information about `APP_OPTIM`, see `APP_OPTIM=release`, and compiles with `-O2`. Results of NDK_DEBUG (command line) andĪndroid:debuggable (manifest) combinations. Results of each possible combination of settings. Optimization-related behavior, and inclusion of symbols. Use the NDK_DEBUG option and, in certain cases,ĪndroidManifest.xml to specify debug or release build, Launch build, and display build commands.įorce a complete rebuild, and display build commands.ĭisplay internal NDK log messages (used for debugging the NDK itself).īuild, using a specific Application.mk file pointed to by theīuild the native code for the project path located at Modifier or selecting a smaller value for N, such as 2. To avoid this issue, consider not using the -j N High number of parallel executions may result in a build error that Note: On Mac OS X, running ndk-build clean with a Remove any previously generated binaries. Project’s root directory, and is the directory whereĪll parameters to ndk-build are passed directly to the underlying GNU makeĬommand that runs the NDK build scripts. To run itįrom the command line, invoke it while in or under your application project directory. The ndk-build script lives in the top level NDK installation directory. This information to invoke ndk-build from other shell scripts, or even your own points to your NDK installation directory. $GNUMAKE points to GNU Make 3.81 or later, and Running the ndk-build script is equivalent to running the following command: There is more specific documentation for the The ndk-build script builds projects that use the NDK's Make-based build
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