FocusVolumeControlPlugin/src/FocusVolumeControl/Native.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;

namespace FocusVolumeControl
{
	public class Native
	{
		public 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")]
		public static extern bool UnhookWinEvent(IntPtr hWinEventHook);


		private const uint WINEVENT_OUTOFCONTEXT = 0;
		private const uint EVENT_SYSTEM_FOREGROUND = 3;

		public static IntPtr RegisterForForegroundWindowChangedEvent(WinEventDelegate dele) => SetWinEventHook(EVENT_SYSTEM_FOREGROUND, EVENT_SYSTEM_FOREGROUND, IntPtr.Zero, dele, 0, 0, WINEVENT_OUTOFCONTEXT);


		[DllImport("user32.dll")]
		public static extern IntPtr GetForegroundWindow();

		[DllImport("user32.dll", SetLastError = true)]
		public static extern uint GetWindowThreadProcessId(IntPtr hWnd, out int processId);

		
		private delegate bool EnumWindowProc(IntPtr hwnd, IntPtr lParam);

		[DllImport("user32")]
		[return: MarshalAs(UnmanagedType.Bool)]
		private static extern bool EnumChildWindows(IntPtr window, EnumWindowProc callback, IntPtr lParam);


		public static List<int> GetProcessesOfChildWindows(IntPtr windowHandle)
		{
			var ids = new List<int>();

			if(windowHandle != IntPtr.Zero)
			{

			EnumChildWindows(windowHandle,
					(hWnd, lParam) => 
					{
						Native.GetWindowThreadProcessId(hWnd, out var pid);
						ids.Add(pid);

					return true;

				}, IntPtr.Zero);
			}

			return ids;
		}


	}
}