missing cv::createLBPHFaceRecognizer() code for java/jni wrap

gistfile1.txt

//
// facerec.cpp, this goes into your dll/so.
// this is just an example for lbp, but it will work similar for fisher and eigen, too.
//


#include "jni.h"
#include "opencv2/contrib/contrib.hpp"

//
// the create****FaceRecognizer functions return a cv::Ptr<FaceRecognizer>.
// if this thing leaves the scope(our function returns), it will destroy the instance.
// so we have to something about that (adding a refcount):
//
template<typename Y>
Y * extractPtr(cv::Ptr<Y> & y)
{
#if (CV_MAJOR_VERSION > 2) // 3.0 / master
    new (&y)cv::Ptr<Y>(y); // inplace new ;)
    return y.get();
#else                      // 2.4
    y.addref();
    return y.obj;
#endif
}


#ifdef __cplusplus
extern "C" {
#endif

// don't worry about the _10 , _1 resolves to a single underscore

JNIEXPORT jlong JNICALL Java_LBPHFaceRecognizer_createLBPHFaceRecognizer_10(JNIEnv* env, jclass);
JNIEXPORT jlong JNICALL Java_LBPHFaceRecognizer_createLBPHFaceRecognizer_10(JNIEnv* env, jclass) {
    try {
        cv::FaceRecognizer * pfr = extractPtr<cv::FaceRecognizer>(cv::createLBPHFaceRecognizer());
        return (jlong) pfr;
    } catch (...) {
        jclass je = env->FindClass("java/lang/Exception");
        env->ThrowNew(je, "sorry, dave..");
    }
    return 0;
}

JNIEXPORT jlong JNICALL Java_LBPHFaceRecognizer_createLBPHFaceRecognizer_11(JNIEnv* env, jclass, jint radius);
JNIEXPORT jlong JNICALL Java_LBPHFaceRecognizer_createLBPHFaceRecognizer_11(JNIEnv* env, jclass, jint radius) {
    try {
        cv::FaceRecognizer * pfr = extractPtr<cv::FaceRecognizer>(cv::createLBPHFaceRecognizer((int)radius));
        return (jlong) pfr;
    } catch (...) {
        jclass je = env->FindClass("java/lang/Exception");
        env->ThrowNew(je, "sorry, dave..");
    }
    return 0;
}

JNIEXPORT jlong JNICALL Java_LBPHFaceRecognizer_createLBPHFaceRecognizer_12(JNIEnv* env, jclass, jint radius, jint neighbours);
JNIEXPORT jlong JNICALL Java_LBPHFaceRecognizer_createLBPHFaceRecognizer_12(JNIEnv* env, jclass, jint radius, jint neighbours) {
    try {
        cv::FaceRecognizer * pfr = extractPtr<cv::FaceRecognizer>(cv::createLBPHFaceRecognizer((int)radius,(int)neighbours));
        return (jlong) pfr;
    } catch (...) {
        jclass je = env->FindClass("java/lang/Exception");
        env->ThrowNew(je, "sorry, dave..");
    } 
    return 0;
}

// and so on for the remaining args ....

#ifdef __cplusplus
}
#endif




//
// --8<--------- snip here ------------------------
//
// LBPHFaceRecognizer.java 
// 


import org.opencv.contrib.FaceRecognizer;
import org.opencv.core.Core;


public class LBPHFaceRecognizer extends FaceRecognizer {

    static{ System.loadLibrary("facerec"); } // for eclipse, the dll goes toplevel into your project dir

    private static native long createLBPHFaceRecognizer_0();
    private static native long createLBPHFaceRecognizer_1(int radius);
    private static native long createLBPHFaceRecognizer_2(int radius,int neighbours);
 
    public LBPHFaceRecognizer() {
    	super(createLBPHFaceRecognizer_0());
    }
    public LBPHFaceRecognizer(int radius) {
    	super(createLBPHFaceRecognizer_1(radius));
    }
    public LBPHFaceRecognizer(int radius,int neighbours) {
    	super(createLBPHFaceRecognizer_2(radius,neighbours));
    }
}


//
// --8<--------- snip here ------------------------
// 
// main java code:
//


    private FaceRecognizer facerec;
    
    public void init()
    {  
        facerec = new LBPHFaceRecognizer(8,8);
    }

This produces a compile error when using clang. Any idea why? How are you creating the library?

facerec.cpp:54:36: error: no matching function for call to 'extractPtr'
    cv::FaceRecognizer * pfr = extractPtr<cv::FaceRecognizer>(cv::createLBPHFaceRecognizer((int)radius,(int)neighbours));
                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
facerec.cpp:16:5: note: candidate function [with Y = cv::FaceRecognizer] not viable: expects an l-value for 1st argument
Y * extractPtr(cv::Ptr<Y> & y)
     ^

ouch, i did not get notified. sorry for the delay.

no, i did not try clang (on win here)

hmm. honestly, i have problems understanding the error.

that extractPtr function is probably way over the top.

for 2.4, might as well try:

 cv::Ptr<cv::FaceRecognizer> pfr = cv::createLBPHFaceRecognizer();
 pfr.addref();
 return (jlong) pfr.obj;

would you be kind giving us a link to your x86 compiled .DLL file ?
here there is no C++ environment installed
thanks in advance!

Hi, I was able to make the .so file, but now I get a "symbol lookup error:" for "undefined symbol: _ZN2cv24createLBPHFaceRecognizerEiiiid"

Is there any fork of opencv repo with implemented JNI wrap like posted here?