chore: import upstream snapshot with attribution

modules/videoio/misc/java/src/cpp/videoio_converters.cpp

@@ -0,0 +1,97 @@
+#include "videoio_converters.hpp"
+
+class JNIEnvHandler
+{
+public:
+    JNIEnvHandler(JavaVM* _vm) : vm(_vm)
+    {
+        jint res = vm->GetEnv((void**)&env, JNI_VERSION_1_6);
+        if (res == JNI_EDETACHED)
+        {
+#ifdef __ANDROID__
+            res = vm->AttachCurrentThread(&env, NULL);
+#else
+            res = vm->AttachCurrentThread((void**)&env, NULL);
+#endif // __ANDROID__
+            detach = true;
+        }
+    }
+
+    ~JNIEnvHandler()
+    {
+        if (env && detach)
+        {
+            vm->DetachCurrentThread();
+        }
+    }
+
+    JavaVM* vm;
+    JNIEnv* env = nullptr;
+    bool detach = false;
+};
+
+JavaStreamReader::JavaStreamReader(JNIEnv* env, jobject _obj)
+{
+    obj = env->NewGlobalRef(_obj);
+    jclass cls = env->GetObjectClass(obj);
+    m_read = env->GetMethodID(cls, "read", "([BJ)J");
+    m_seek = env->GetMethodID(cls, "seek", "(JI)J");
+    env->GetJavaVM(&vm);
+}
+
+JavaStreamReader::~JavaStreamReader()
+{
+    JNIEnvHandler handler(vm);
+    JNIEnv* env = handler.env;
+    if (!env)
+        return;
+    env->DeleteGlobalRef(obj);
+}
+
+long long JavaStreamReader::read(char* buffer, long long size)
+{
+    if (!m_read)
+        return 0;
+    JNIEnvHandler handler(vm);
+    JNIEnv* env = handler.env;
+    if (!env)
+        return 0;
+    jbyteArray jBuffer = env->NewByteArray(static_cast<jsize>(size));
+    if (!jBuffer)
+        return 0;
+    jlong res = env->CallLongMethod(obj, m_read, jBuffer, size);
+    env->GetByteArrayRegion(jBuffer, 0, static_cast<jsize>(size), reinterpret_cast<jbyte*>(buffer));
+    env->DeleteLocalRef(jBuffer);
+    return res;
+}
+
+long long JavaStreamReader::seek(long long offset, int way)
+{
+    JNIEnvHandler handler(vm);
+    JNIEnv* env = handler.env;
+    if (!env)
+        return 0;
+    if (!m_seek)
+        return 0;
+    return env->CallLongMethod(obj, m_seek, offset, way);
+}
+
+// Same as dnn::vector_Target_to_List
+jobject vector_VideoCaptureAPIs_to_List(JNIEnv* env, std::vector<cv::VideoCaptureAPIs>& vs)
+{
+    static jclass juArrayList   = ARRAYLIST(env);
+    static jmethodID m_create   = CONSTRUCTOR(env, juArrayList);
+    jmethodID m_add       = LIST_ADD(env, juArrayList);
+
+    static jclass jInteger = env->FindClass("java/lang/Integer");
+    static jmethodID m_create_Integer = env->GetMethodID(jInteger, "<init>", "(I)V");
+
+    jobject result = env->NewObject(juArrayList, m_create, vs.size());
+    for (size_t i = 0; i < vs.size(); ++i)
+    {
+        jobject element = env->NewObject(jInteger, m_create_Integer, vs[i]);
+        env->CallBooleanMethod(result, m_add, element);
+        env->DeleteLocalRef(element);
+    }
+    return result;
+}

modules/videoio/misc/java/src/cpp/videoio_converters.hpp

@@ -0,0 +1,25 @@
+#ifndef VIDEOIO_CONVERTERS_HPP
+#define VIDEOIO_CONVERTERS_HPP
+
+#include <jni.h>
+#include "opencv_java.hpp"
+#include "opencv2/core.hpp"
+#include "opencv2/videoio.hpp"
+
+class JavaStreamReader : public cv::IStreamReader
+{
+public:
+    JavaStreamReader(JNIEnv* env, jobject obj);
+    ~JavaStreamReader();
+    long long read(char* buffer, long long size) CV_OVERRIDE;
+    long long seek(long long offset, int way) CV_OVERRIDE;
+
+private:
+    JavaVM* vm;
+    jobject obj;
+    jmethodID m_read, m_seek;
+};
+
+jobject vector_VideoCaptureAPIs_to_List(JNIEnv* env, std::vector<cv::VideoCaptureAPIs>& vs);
+
+#endif