using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace ThumbnailViewer
{
    public partial class Form1 : Form
    {
        // DWM Structs.
        [StructLayout(LayoutKind.Sequential)]
        internal struct PSIZE
        {
            public int x;
            public int y;
        }

        [StructLayout(LayoutKind.Sequential)]
        internal struct Rect
        {
            internal Rect(int left, int top, int right, int bottom)
            {
                Left = left;
                Top = top;
                Right = right;
                Bottom = bottom;
            }
            public int Left;
            public int Top;
            public int Right;
            public int Bottom;
        }

        [StructLayout(LayoutKind.Sequential)]
        internal struct DWM_THUMBNAIL_PROPERTIES
        {
            public int dwFlags;
            public Rect rcDestination;
            public Rect rcSource;
            public byte opacity;
            public bool fVisible;
            public bool fSourceClientAreaOnly;
        }

        // DWM APIs.
        [DllImport("dwmapi.dll")]
        static extern int DwmRegisterThumbnail(IntPtr dest, IntPtr src, out IntPtr thumb);

        [DllImport("dwmapi.dll")]
        static extern int DwmUnregisterThumbnail(IntPtr thumb);

        [DllImport("dwmapi.dll")]
        static extern int DwmQueryThumbnailSourceSize(IntPtr thumb, out PSIZE size);

        [DllImport("dwmapi.dll")]
        static extern int DwmUpdateThumbnailProperties(IntPtr hThumb, ref DWM_THUMBNAIL_PROPERTIES props);

        static readonly int DWM_TNP_VISIBLE = 0x8;
        static readonly int DWM_TNP_OPACITY = 0x4;
        static readonly int DWM_TNP_RECTDESTINATION = 0x1;

        // Thumbnail Handle.
        private IntPtr thumb;

        // Running ProcessList.
        private Process[] processList;

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            // Create processList to ComboBox.
            processList = Process.GetProcesses();
            foreach (Process process in processList)
            {
                comboBox1.Items.Add(process.ProcessName);
            }
        }

        private void Form1_FormClosed(object sender, FormClosedEventArgs e)
        {
            ReleaseThumb();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            // Release Exist Thumbnail.
            ReleaseThumb();

            // Regist New Thumbnail.
            foreach (Process process in processList)
            {
                String processName = process.ProcessName;
                int pid = process.Id;

                if (processName.Equals(this.comboBox1.SelectedItem))
                {
                    IntPtr hWnd = process.MainWindowHandle;
                    int i = DwmRegisterThumbnail(this.Handle, hWnd, out thumb);
                    UpdateThumb();
                    break;
                }
            }
        }

        private void UpdateThumb()
        {
            if (thumb != IntPtr.Zero)
            {
                PSIZE size;
                DwmQueryThumbnailSourceSize(thumb, out size);

                DWM_THUMBNAIL_PROPERTIES props = new DWM_THUMBNAIL_PROPERTIES();

                props.fVisible = true;
                props.dwFlags = DWM_TNP_VISIBLE | DWM_TNP_RECTDESTINATION | DWM_TNP_OPACITY;
                props.opacity = 255;
                props.rcDestination = new Rect(pictureBox1.Left, pictureBox1.Top, pictureBox1.Right, pictureBox1.Bottom);

                DwmUpdateThumbnailProperties(thumb, ref props);
            }
        }

        private void ReleaseThumb()
        {
            if (thumb != IntPtr.Zero)
            {
                DwmUnregisterThumbnail(thumb);
                thumb = IntPtr.Zero;
            }
        }


    }   // End of ThumbnailViewer Class.
}