openCV java code pass Point object to native code(C++)?

For a point i recomend just passing x and y as doubles. For MatOfPoints and others:

OpenCV comes with converters that store different kind of stuff in a Mat.

There is the converter on the java side, that is part of the opencv-android-sdk org.opencv.utils.Converters

There is also a C++ converter i found in the opencv repo, but the header is not included in the opencv-android-sdk, and i couldn't get it working with just adding the header so i copied the converters.h and converters.cpp to my jni folder and corrected the imports to point to the right place (but this might not be necessary).

https://github.com/Itseez/opencv/blob/master/modules/java/generator/src/cpp/converters.cpp

This converters can be used to pass MatOfPoint or List and a lot more to your native code, where you have to convert it again to a c++ type (c++ equivalent of MatOfPoint is std::vector< cv::Point >; equivalent of List is std::vector< std::vector< cv::Point > >)

With this converters you can "convert" a MatOfPoint to a Mat and back using vector_Point_to_Mat or Mat_to_vector_Point (returns a List but with MatOfPoint.fromList you get a MatOfPoint from that)

Here is an example how to pass List to native level and a MatOfPoint back.

Java code:

public class YourJavaWrapper {

    static {
        System.loadLibrary("yourlibrary");
    }

    public static MatOfPoint findMostFencyMatOfPoints(List<MatOfPoint> contours){

        List<Mat> contoursTmp = new ArrayList<Mat>(contours.size());
        Mat inputMat = Converters.vector_vector_Point_to_Mat(contours, contoursTmp);
        Mat outputMat = new Mat();

        findMostFencyMatOfPoints(inputMat.nativeObj, outputMat.nativeObj);

        List<Point> pointsTmp = new ArrayList<Point>();
        Converters.Mat_to_vector_Point(outputMat, pointsTmp);
        MatOfPoint matOfInterest = new MatOfPoint();
        matOfInterest.fromList(pointsTmp);
        outputMat.release();

        return matOfInterest;
    }

    private static native void findMostFencyMatOfPoints(long inputMatAddress, long outPutMatAddress);

}

C++ code:

using namespace std;
using namespace cv;

extern "C" JNIEXPORT void JNICALL Java_org_example_yourpackage_YourJavaWrapper_findMostFencyMatOfPoints(JNIEnv*, jobject, jlong inputMatAddress, jlong outPutMatAddress)
{
    cv::Mat& vectorVectorPointMat = *(cv::Mat*) inputMatAddress;
    std::vector< std::vector< cv::Point > > contours;
    Mat_to_vector_vector_Point(vectorVectorPointMat, contours);
    std::vector<cv::Point> fencyVectorOfPoints = findMostFencyVectorOfPoint(contours);
    cv::Mat& largestSquareMat = *(cv::Mat*) outPutMatAddress;
    vector_Point_to_Mat(fencyVectorOfPoints, outPutMatAddress);
}

in this example findMostFencyVectorOfPoint is your custom native function