BitBlt 函数 详解， StretchBlt、SetStretchBltMode、SetBrushOrgEx 按句柄截图、直接截取缩略图

    public static classImageHelper
    {
        public static Bitmap CaptureWindow(IntPtr handle, int width, intheight)
        {
            try
            {
                //get the hDC of the target window
                IntPtr hdcSrc =User32.GetWindowDC(handle);
                //create a device context we can copy to
                IntPtr hdcDest =GDI32.CreateCompatibleDC(hdcSrc);
                //create a bitmap we can copy it to,
                //using GetDeviceCaps to get the width/height
                IntPtr hBitmap =GDI32.CreateCompatibleBitmap(hdcSrc, width, height);
                //select the bitmap object
                IntPtr hOld =GDI32.SelectObject(hdcDest, hBitmap);
                //bitblt over
                GDI32.BitBlt(hdcDest, 0, 0, width, height, hdcSrc, 0, 0, GDI32.SRCCOPY);
                //restore selection
GDI32.SelectObject(hdcDest, hOld);
                //clean up 
GDI32.DeleteDC(hdcDest);
                User32.ReleaseDC(handle, hdcSrc);
                //get a .NET image object for it
                Bitmap img =Image.FromHbitmap(hBitmap);
                //free up the Bitmap object
GDI32.DeleteObject(hBitmap);
                returnimg;
            }
            catch(Exception ex)
            {
                LogHelper.Execption(ex, nameof(ImageHelper));
            }
            return null;
        }
        public static Bitmap CaptureWindow(IntPtr handle, int widthSrc, int heightSrc, int widthDest, intheightDest)
        {
            try
            {
                //get the hDC of the target window
                IntPtr hdcSrc =User32.GetWindowDC(handle);
                //create a device context we can copy to
                IntPtr hdcDest =GDI32.CreateCompatibleDC(hdcSrc);
                //create a bitmap we can copy it to,
                //using GetDeviceCaps to get the width/height
                IntPtr hBitmap =GDI32.CreateCompatibleBitmap(hdcSrc, widthDest, heightDest);
                //select the bitmap object
                IntPtr hOld =GDI32.SelectObject(hdcDest, hBitmap);
                GDI32.SetStretchBltMode(hdcDest, GDI32.STRETCH_HALFTONE);
                GDI32.POINTAPI point;
                GDI32.SetBrushOrgEx(hdcDest, 0, 0, outpoint);
                //bitblt over
                GDI32.StretchBlt(hdcDest, 0, 0, widthDest, heightDest, hdcSrc, 0, 0, widthSrc, heightSrc, GDI32.SRCCOPY);
                //restore selection
GDI32.SelectObject(hdcDest, hOld);
                //clean up 
GDI32.DeleteDC(hdcDest);
                User32.ReleaseDC(handle, hdcSrc);
                //get a .NET image object for it
                Bitmap img =Image.FromHbitmap(hBitmap);
                //free up the Bitmap object
GDI32.DeleteObject(hBitmap);
                returnimg;
            }
            catch(Exception ex)
            {
                LogHelper.Execption(ex, nameof(ImageHelper));
            }
            return null;
        }
        /// <summary>  
        ///Helper class containing Gdi32 API functions  
        /// </summary>  
        public classGDI32
        {
            public const int CAPTUREBLT = 1073741824;
            public const int SRCCOPY = 0x00CC0020; //BitBlt dwRop parameter  
            [DllImport("gdi32.dll")]
            public static extern bool BitBlt(IntPtr hObject, int nXDest, intnYDest,
                int nWidth, intnHeight, IntPtr hObjectSource,
                int nXSrc, int nYSrc, intdwRop);
            [DllImport("gdi32.dll")]
            public static extern IntPtr CreateCompatibleBitmap(IntPtr hDC, intnWidth,
                intnHeight);
            [DllImport("gdi32.dll")]
            public static externIntPtr CreateCompatibleDC(IntPtr hDC);
            [DllImport("gdi32.dll")]
            public static extern boolDeleteDC(IntPtr hDC);
            [DllImport("gdi32.dll")]
            public static extern boolDeleteObject(IntPtr hObject);
            [DllImport("gdi32.dll")]
            public static externIntPtr SelectObject(IntPtr hDC, IntPtr hObject);
            /// <summary>
            ///缩放截图
            /// </summary>
            /// <param name="hdcDest"></param>
            /// <param name="nXOriginDest"></param>
            /// <param name="nYOriginDest"></param>
            /// <param name="nWidthDest"></param>
            /// <param name="nHeightDest"></param>
            /// <param name="hdcSrc"></param>
            /// <param name="nXOriginSrc"></param>
            /// <param name="nYOriginSrc"></param>
            /// <param name="nWidthSrc"></param>
            /// <param name="nHeightSrc"></param>
            /// <param name="dwRop"></param>
            /// <returns></returns>
            [DllImport("gdi32.dll")]
            public static extern bool StretchBlt(IntPtr hdcDest, int nXOriginDest, int nYOriginDest, int nWidthDest, intnHeightDest,
                IntPtr hdcSrc, int nXOriginSrc, int nYOriginSrc, int nWidthSrc, int nHeightSrc, intdwRop);
            public const int STRETCH_ANDSCANS = 0x01;
            public const int STRETCH_ORSCANS = 0x02;
            public const int STRETCH_DELETESCANS = 0x03;
            public const int STRETCH_HALFTONE = 0x04;
            /// <summary>
            ///设置缩放模式
            /// </summary>
            /// <param name="hdc"></param>
            /// <param name="iStretchMode"></param>
            /// <returns>失败返回0</returns>
            [DllImport("gdi32.dll")]
            public static extern int SetStretchBltMode(IntPtr hdc, intiStretchMode);
            [StructLayout(LayoutKind.Sequential)]
            public structPOINTAPI
            {
                public intx;
                public inty;
            }
            [DllImport("gdi32.dll")]
            public static extern bool SetBrushOrgEx(IntPtr hdc, int nXOrg, int nYOrg, outPOINTAPI lppt);
        }
        /// <summary>  
        ///Helper class containing User32 API functions  
        /// </summary>  
        public classUser32
        {
            [StructLayout(LayoutKind.Sequential)]
            public structRECT
            {
                public intleft;
                public inttop;
                public intright;
                public intbottom;
            }
            [DllImport("user32.dll")]
            public static externIntPtr GetDesktopWindow();
            [DllImport("user32.dll")]
            public static externIntPtr GetWindowDC(IntPtr hWnd);
            [DllImport("user32.dll")]
            public static externIntPtr ReleaseDC(IntPtr hWnd, IntPtr hDC);
            [DllImport("user32.dll")]
            public static extern IntPtr GetWindowRect(IntPtr hWnd, refRECT rect);
            public const int WM_PAINT = 0x000F;
            [DllImport("user32.dll", EntryPoint = "SendMessageA")]
            public static extern uint SendMessage(IntPtr hWnd, intwMsg, IntPtr wParam, IntPtr lParam);
            [DllImport("user32.dll")]
            public static extern boolPrintWindow(
                IntPtr hwnd,                //Window to copy,Handle to the window that will be copied.
                IntPtr hdcBlt,              //HDC to print into,Handle to the device context.
                UInt32 nFlags               //Optional flags,Specifies the drawing options. It can be one of the following values.
);
            [DllImport("user32.dll", CharSet = CharSet.Auto, ExactSpelling = true)]
            public static extern int ShowWindow(IntPtr hwnd, intnCmdShow);
            #region  窗口关联
            //nCmdShow的含义
            //0 关闭窗口
            //1 正常大小显示窗口
            //2 最小化窗口
            //3 最大化窗口
            //使用实例: ShowWindow(myPtr, 0);
            #endregion
        }
    }