worked with OpenCV on C++, now it’s time to do it on android. How to connect the old C++ project to jni?

Answer 1, Authority 100%

1. Download NDK – Native Development Kit
2. set ndk – specifically decide on toolchain
3. Plant your source in Tree SRC / JNI
4. Write make Make files for building sources: Application.mk and Android.mk
5. Register in Gradle rules of construction (I do not use it – therefore I will not tell you, I usually collect from the command line)
6. Write JNI Interfaces – Bundles between C++ and Java code
7. Collect, in the end you will receive 3 or 4 lips for different platforms: ABI x86 , arm , etc.

Perhaps the instruction is slightly outdated, I have not codified C++ under Android