[C#]スクリーンキャプチャで非クライアント領域のみ重なってキャプチャされる。

    public partial class Form1 : Form
    {
        private const int SRCCOPY = 13369376;
        private const int DWMWA_EXTENDED_FRAME_BOUNDS = 9;
        [StructLayout(LayoutKind.Sequential)]
        private struct Rect
        {
            public int left;
            public int top;
            public int right;
            public int bottom;
        }

        [DllImport("user32.dll")]
        static extern IntPtr GetWindowRect(IntPtr hWnd, out Rect rect);

        [DllImport("user32.dll")]
        private static extern IntPtr GetDC(IntPtr hwnd);

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

        [DllImport("dwmapi.dll")]
        extern static int DwmGetWindowAttribute(IntPtr hWnd, int dwAttribute, out Rect rect, int cbAttribute);

        [DllImport("user32.dll")]
        static extern IntPtr GetWindowDC(IntPtr hWnd);

        [DllImport("gdi32.dll")]
        static extern int BitBlt(IntPtr hDestDC, int x, int y, int nWidth, int nHeight, IntPtr hSrcDC, int xSrc, int ySrc, int dwRop);

        [DllImport("user32.dll")]
        static extern IntPtr ReleaseDC(IntPtr hWnd, IntPtr hdc);

        [DllImport("user32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        private static extern bool SetForegroundWindow(IntPtr hWnd);
        IntPtr hWnd;

        public Form1()
        {
            InitializeComponent();
            this.AutoScroll = true;
            button2.Text = "false";
        }

        private void Button1_Click(object sender, EventArgs e)
        {
            if (timer1.Enabled)
            {
                timer1.Enabled = false;
                button2.Text = "false";
            }
            else
            {
                // キャプチャの対象とするwindowのハンドルを取得する。
                System.Diagnostics.Process[] TargetP = GetMainProcess("TestBench");
                if (TargetP.Length != 1) return;
                hWnd = TargetP[0].MainWindowHandle;

                timer1.Enabled = true;
                button2.Text = "true";
            }
        }

        public Bitmap CaptureWindow(IntPtr hWnd)
        {
            // SetForegroundWindow(hWnd);
            // 対象のウィンドウをフォアグランドにしてからCaptureすれば問題は起こらないが、
            // 別のウィンドウの表示が隠れてしまうので、出来ればフォアグランドにしたくない。

            Rect bounds, rect;
            IntPtr winDC = GetWindowDC(hWnd);
            DwmGetWindowAttribute(hWnd, DWMWA_EXTENDED_FRAME_BOUNDS, out bounds, Marshal.SizeOf(typeof(Rect)));
            GetWindowRect(hWnd, out rect);
            var offsetX = bounds.left - rect.left;
            var offsetY = bounds.top - rect.top;
            Bitmap bitmap = new Bitmap(bounds.right - bounds.left, bounds.bottom - bounds.top);
            Graphics graphics = Graphics.FromImage(bitmap);
            IntPtr hDC = graphics.GetHdc();
            BitBlt(hDC, 0, 0, bitmap.Width, bitmap.Height, winDC, offsetX, offsetY, SRCCOPY);
            graphics.ReleaseHdc(hDC);
            graphics.Dispose();
            ReleaseDC(hWnd, winDC);
            return bitmap;
        }


        private void timer1_Tick(object sender, EventArgs e)
        {
            pictureBox1.Image = CaptureWindow(hWnd);

        }


        public static System.Diagnostics.Process[] GetMainProcess(string TargetTitle)
        {
            List<System.Diagnostics.Process> TargetP = new List<System.Diagnostics.Process>();

            /* 現在稼働中のプロセスを取得 */
            foreach (System.Diagnostics.Process p in System.Diagnostics.Process.GetProcesses())
            {
                if (p.ProcessName.Contains(TargetTitle))
                {
                    TargetP.Add(p);
                }
            }
            System.Diagnostics.Process[] ret = new System.Diagnostics.Process[TargetP.Count];
            int i = 0;
            foreach (System.Diagnostics.Process p in TargetP)
            {
                ret[i] = p;
                i++;
            }
            return ret;
        }


    }