Native window decorations: initial implementation in C++ using JNI

flatlaf-natives/flatlaf-natives-windows/src/main/cpp/Registry.cpp

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+/*
+ * Copyright 2021 FormDev Software GmbH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <windows.h>
+#include <winreg.h>
+#include <winerror.h>
+#include <jni.h>
+#include "com_formdev_flatlaf_ui_FlatWindowsNativeWindowBorder.h"
+
+/**
+ * @author Karl Tauber
+ */
+
+//---- JNI methods ------------------------------------------------------------
+
+extern "C"
+JNIEXPORT jint JNICALL Java_com_formdev_flatlaf_ui_FlatWindowsNativeWindowBorder_registryGetIntValue
+	( JNIEnv* env, jclass cls, jstring key, jstring valueName, jint defaultValue )
+{
+	const char* skey = env->GetStringUTFChars( key, NULL );
+	const char* svalueName = env->GetStringUTFChars( valueName, NULL );
+
+	DWORD data = 0;
+	DWORD cbData = sizeof( data );
+	int rc = ::RegGetValueA( HKEY_CURRENT_USER, skey, svalueName, RRF_RT_DWORD, NULL, &data, &cbData );
+
+	env->ReleaseStringUTFChars( key, skey );
+	env->ReleaseStringUTFChars( valueName, svalueName );
+
+	return (rc == ERROR_SUCCESS) ? data : defaultValue;
+}