Access struct directly of c++ from java code - javacpp

Question

I am new to javacpp i know java have not much experience in c++. This might be one of very simple question but i am struggling with this. How to access any variable type value written in header of c++ into java code using javacpp. Let us consider example:
C++ Code example:
There is function written in C++ which return the frame of video below is the code for it and expects an Struct argument to be passed.
unsigned char *
Videodecode::getframe_data (void *ptr)
{
GstSample *sample;
GstBuffer *buffer;
GstMapInfo map;
GstCaps *caps;
GstStructure *str;
gint width, height;
gstData *dataa = (gstData *) ptr;
sample = gst_app_sink_pull_sample ((GstAppSink*)dataa->sink);
if (sample != NULL) {
buffer = gst_sample_get_buffer (sample);
gst_buffer_map (buffer, &map, GST_MAP_READ);
if (map.data != NULL) {
caps = gst_sample_get_caps (sample);
if (caps != NULL);
str = gst_caps_get_structure (caps, 0);
if (!gst_structure_get_int (str, "width", &width) ||
!gst_structure_get_int (str, "height", &height)) {
g_print ("No width/height available\n");
}
display_data = map.data;
//displayImg = Mat (Size (width, height ), CV_8UC3, map.data);
// cvtColor (displayImg, displayImg, COLOR_YUV2BGR_YUY2);
gst_buffer_unmap (buffer, &map);
gst_buffer_unref (buffer);
} else
gst_sample_unref (sample);
}
else {
//cout << "gstImageBuffer is NULL" << endl;
return NULL;
}
//return displayImg.data;
return display_data;
}
The structure which need to be passed as argument is below
typedef struct gstData_t
{
GstElement *pipeline;
GstElement *source;
GstElement *demux;
GstElement *parser;
GstElement *decoder;
GstElement *convert;
GstElement *capsfilter;
GstElement *sink;
GstElement *typefind;
} gstData;
Corresponding java code written to access it is below:
import java.io.File;
import java.io.IOException;
import java.nio.ByteBuffer;
import org.bytedeco.javacpp.FunctionPointer;
import org.bytedeco.javacpp.Loader;
import org.bytedeco.javacpp.Pointer;
import org.bytedeco.javacpp.annotation.Name;
import org.bytedeco.javacpp.annotation.NoOffset;
import org.bytedeco.javacpp.annotation.Platform;
import org.bytedeco.javacpp.annotation.Raw;
import org.bytedeco.javacpp.tools.Builder;
import org.bytedeco.javacpp.tools.ParserException;
#Platform(include = {"Videodecode.h",
},
includepath = {"/usr/include/gstreamer-1.0/","/usr/include/glib-2.0/","/usr/lib/x86_64-linux-gnu/glib-2.0/include/"},
//linkpath = {"/home/ign/git/JavaCppExample/src/main/resources/de/oltzen/javacppexample/"},
link = {"Videodecode"})
public class Videodecode {
NativeVideodecode nda;
static {
Class c = Videodecode.class;
Builder builder = null;
try {
builder = new Builder().classesOrPackages(c.getName());
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (NoClassDefFoundError e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
File[] outputFiles = builder.build();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ParserException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Loader.load(c);
// Loader.load();
}
public Videodecode() {
nda = new NativeVideodecode();
}
public Videodecode(String filename) {
nda = new NativeVideodecode(filename);
}
public boolean filePathCpp(String str){
return nda.filePathCpp(str);
}
public boolean settingValCpp(String str){
return nda.settingValCpp(str);
}
public boolean process_event (int event) {
return nda.process_event(event);
}
public java.nio.ByteBuffer test1122 (String buffer) {
return nda.test1122(buffer);
}
public java.nio.ByteBuffer test112233 (String buffer) {
return nda.test1122(buffer);
}
public java.nio.ByteBuffer getframe_data(java.nio.ByteBuffer buffer){
return nda.getframe_data(buffer);
}
public Pointer gstData(){
return nda.gstData();
}
#Name("Videodecode")
public static class NativeVideodecode extends Pointer {
static {
Loader.load();
}
public NativeVideodecode() {
allocate();
}
public NativeVideodecode(String filename) {
System.out.println("filename "+filename);
allocate(filename);
}
public NativeVideodecode(Pointer p) {
super(p);
}
private native void allocate(String filename);
private native void allocate();
private native boolean filePathCpp(String str);
private native boolean settingValCpp(String str);
private native boolean process_event(int event);
private native java.nio.ByteBuffer test1122(String buffer);
private native java.nio.ByteBuffer test112233(String buffer);
// private native boolean test1122(byte[] buffer);
private native java.nio.ByteBuffer getframe_data (java.nio.ByteBuffer buffer);
#NoOffset private native Pointer gstData();
}
}
Problems being faced by me :
How to access Struct from C++ and pass it as an argument using java.
How to access frame data which is unsigned char*.
Approach which i tried to perform this.
To access Struct, i tried using offsetof but not sure how to use it in javacpp.
To access frame data i tried using java.nio.ByteBuffer but seems its not working properly.
While trying to compile code using mvn clean install below error is getting triggered.
[INFO] --- javacpp:1.3:build (javacpp.compiler) # projecustom ---
[INFO] Detected platform "linux-x86_64"
[INFO] Building for platform "linux-x86_64"
[WARNING] Could not load platform properties for class com.proje.decoder.connectorJavaCpp
[WARNING] Could not load platform properties for class com.proje.decoder.test1234
[INFO] Generating /home/ign/eclipse-workspace/projecustom/target/classes/com/proje/decoder/jniVideodecode.cpp
[INFO] Compiling /home/ign/eclipse-workspace/projecustom/target/classes/com/proje/decoder/linux-x86_64/libjniVideodecode.so
[INFO] g++ -I/usr/include/gstreamer-1.0/ -I/usr/include/glib-2.0/ -I/usr/lib/x86_64-linux-gnu/glib-2.0/include/ -I/usr/lib/jvm/java-8-openjdk-amd64/include -I/usr/lib/jvm/java-8-openjdk-amd64/include/linux /home/ign/eclipse-workspace/projecustom/target/classes/com/proje/decoder/jniVideodecode.cpp -march=x86-64 -m64 -O3 -s -Wl,-rpath,$ORIGIN/ -Wl,-z,noexecstack -Wl,-Bsymbolic -Wall -fPIC -shared -o libjniVideodecode.so -lVideodecode
/home/ign/eclipse-workspace/projecustom/target/classes/com/proje/decoder/jniVideodecode.cpp: In function ‘_jobject* Java_com_proje_decoder_Videodecode_00024NativeVideodecode_gstData(JNIEnv*, jobject)’:
/home/ign/eclipse-workspace/projecustom/target/classes/com/proje/decoder/jniVideodecode.cpp:1532:21: error: ‘class Videodecode’ has no member named ‘gstData’
rptr = ptr->gstData();
edit:
let me try to take one simple example :
C++ Code:
#include <stdio.h>
struct test
{
int a;
std::string b;
};
class Foo {
public:
int n;
int m=70;
test tst;
// tst.a=10;
// tst.b="hi";
Foo(int n) : n(n) { }
virtual ~Foo() { }
virtual void bar() {
printf("Callback in C++ (n == %d)\n", n);
}
};
void callback(Foo *foo) {
foo->bar();
}
is it possible to write modify java code below to access a and b variables of struct
package com.ign.examples;
import org.bytedeco.javacpp.*;
import org.bytedeco.javacpp.annotation.*;
#Platform(include="Foo.h")
public class VirtualFoo1 {
static { Loader.load(); }
public static class Foo extends Pointer {
static { Loader.load(); }
public Foo(int n) { allocate(n); }
private native void allocate(int n);
#NoOffset public native int n(); public native Foo n(int n);
#Virtual public native void bar();
public native int m(); public native void m(int m);
// public native #Cast("int") int a(); public native Foo a(int a);
public native Pointer tst(); public native void tst(Pointer tst);
}
public static native void callback(Foo foo);
public static void main(String[] args) {
Foo foo = new Foo(13);
System.out.println(foo.m());
}
}