Inital commit

src/FocusVolumeControl/Native.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace FocusVolumeControl
+{
+    internal class Native
+    {
+        internal delegate void WinEventDelegate(IntPtr hWinEventHook, uint eventType, IntPtr hwnd, int idObject, int idChild, uint dwEventThread, uint dwmsEventTime);
+
+        [DllImport("user32.dll")]
+        static extern IntPtr SetWinEventHook(uint eventMin, uint eventMax, IntPtr hmodWinEventProc, WinEventDelegate lpfnWinEventProc, uint idProcess, uint idThread, uint dwFlags);
+
+        [DllImport("user32.dll")]
+        internal static extern bool UnhookWinEvent(IntPtr hWinEventHook);
+
+
+        private const uint WINEVENT_OUTOFCONTEXT = 0;
+        private const uint EVENT_SYSTEM_FOREGROUND = 3;
+
+        internal static IntPtr RegisterForForegroundWindowChangedEvent(WinEventDelegate dele) => SetWinEventHook(EVENT_SYSTEM_FOREGROUND, EVENT_SYSTEM_FOREGROUND, IntPtr.Zero, dele, 0, 0, WINEVENT_OUTOFCONTEXT);
+
+
+        [DllImport("user32.dll")]
+        internal static extern IntPtr GetForegroundWindow();
+
+        [DllImport("user32.dll", SetLastError = true)]
+        internal static extern uint GetWindowThreadProcessId(IntPtr hWnd, out int processId);
+
+    }
+}