using System;
using System.Collections.Generic;
using System.Windows.Forms;
using System.ComponentModel;
using System.Drawing;
using System.Runtime.InteropServices;

namespace Experiment_VS_Graphics_FromHwnd
{
    public class Form1 : Form
    {
        private IContainer components = null;
        private Timer timer1;
        System.Diagnostics.Process visualStudio;
        HashSet<IntPtr> windowHandles = new HashSet<IntPtr>();

        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        private void InitializeComponent()
        {
            this.components = new System.ComponentModel.Container();
            this.timer1 = new System.Windows.Forms.Timer(this.components);
            this.SuspendLayout();
            //
            // timer1
            //
            this.timer1.Enabled = true;
            this.timer1.Interval = 5000;
            this.timer1.Tick += new System.EventHandler(this.timer1_Tick);
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(284, 262);
            this.Name = "Form1";
            this.Text = "Form1";
            this.ResumeLayout(false);

        }

        public Form1()
        {
            InitializeComponent();
            visualStudio = System.Diagnostics.Process.GetProcessesByName("devenv")[0];
            EnumWindows(WindowReceiver, IntPtr.Zero); //populate windowHandles with top level windows
        }

        void EnumerateWindowsRecursivelyImpl(IntPtr hWnd)
        {
            if (hWnd == IntPtr.Zero || !windowHandles.Add(hWnd)) return;
            EnumerateWindowsRecursivelyImpl(GetWindow(hWnd, (uint)GetWindow_Cmd.GW_CHILD));
            EnumerateWindowsRecursivelyImpl(GetWindow(hWnd, (uint)GetWindow_Cmd.GW_HWNDNEXT));
        }

        bool WindowReceiver(IntPtr hWnd, IntPtr dontCare)
        {
            uint pid;
            GetWindowThreadProcessId(hWnd, out pid);
            if (pid == (uint)visualStudio.Id)
            {
                windowHandles.Add(hWnd);
                EnumerateWindowsRecursivelyImpl(GetWindow(hWnd, (uint)GetWindow_Cmd.GW_CHILD));
            }
            return true;
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            windowHandles.Clear();
            EnumWindows(WindowReceiver, IntPtr.Zero); //populate windowHandles with top level windows
            foreach (var window in windowHandles)
            {
                var gfx = Graphics.FromHwnd(window);
                gfx.DrawString("Have fun!", Font, Brushes.Black, 10, 10);
                gfx.Dispose();
            }
        }

        private delegate bool EnumWindowsProc(IntPtr hWnd, IntPtr lParam);

        [DllImport("user32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        static extern bool EnumWindows(EnumWindowsProc lpEnumFunc, IntPtr lParam);

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

        [DllImport("user32.dll", SetLastError = true)]
        static extern IntPtr GetWindow(IntPtr hWnd, uint uCmd);

        enum GetWindow_Cmd : uint
        {
            GW_HWNDFIRST = 0,
            GW_HWNDLAST = 1,
            GW_HWNDNEXT = 2,
            GW_HWNDPREV = 3,
            GW_OWNER = 4,
            GW_CHILD = 5,
            GW_ENABLEDPOPUP = 6
        }


    }

    static class Program
    {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }
}