将控件保存为图片

                                        将控件保存为图片

                                                 周银辉

这里分别提供win form 和 wpf 两种方式

对于.net 2.0 我们可以简单地利用 BitBlt 函数来实现，非常简单，代码如下：

    public static class ControlToImageConverter
    {
        private const Int32 SRCCOPY = 0xCC0020;

        [DllImport("gdi32.dll")]
        internal static extern bool BitBlt(
            IntPtr hdcDest, // handle to destination DC
            int nXDest, // x-coord of destination upper-left corner
            int nYDest, // y-coord of destination upper-left corner
            int nWidth, // width of destination rectangle
            int nHeight, // height of destination rectangle
            IntPtr hdcSrc, // handle to source DC
            int nXSrc, // x-coordinate of source upper-left corner
            int nYSrc, // y-coordinate of source upper-left corner
            Int32 dwRop // raster operation code
            );


        public static Bitmap GetImageOfControl(Control control)
        {

            var w = control.Size.Width;
            var h = control.Size.Height;

            Graphics gOfCtrl = control.CreateGraphics();
            var bmp = new Bitmap(w, h, gOfCtrl);

            Graphics gOfBmp = Graphics.FromImage(bmp);

            IntPtr dc1 = gOfCtrl.GetHdc();
            IntPtr dc2 = gOfBmp.GetHdc();

            BitBlt(dc2, 0, 0, w, h, dc1, 0, 0, SRCCOPY);

            gOfCtrl.ReleaseHdc(dc1);
            gOfBmp.ReleaseHdc(dc2);

            gOfCtrl.Dispose();
            gOfBmp.Dispose();


            return bmp;
        }

    }

其中 SRCCOPY = 0xCC0020， 表示将源直接拷贝到目标。

对于WPF，无法获得控件的hdc, 所以不能使用bitblt函数了，但幸运的是，其提供了一个RenderTargetBitmap的类型，可以将控件绘制到改类型的类型是示例上,比如：

var renderBitmap = 
         new RenderTargetBitmap(w, h, 96d,96d, PixelFormats.Pbgra32);

renderBitmap.Render(controlToConvert);

其可以直接作为Image控件的源以便显示，如果要将其保存下来（保存到流中），则需要用到BitmapEncoder, 将上面的位图添加到encoder的帧中，然后调用save方法便可。

包装好的代码如下：

    internal enum ImageType
    {
        Bmp,
        Gif,
        Jpeg,
        Png,
        Tiff,
        Wdp
    }

    internal static class ControlToImageConverter
    {

        /// <summary>
        /// Convert any control to a PngBitmapEncoder
        /// </summary>
        /// <param name="controlToConvert">The control to convert to an ImageSource</param>
        /// <param name="imageType">The image type will indicate the type of return bitmap encoder</param>
        /// <returns>The returned ImageSource of the controlToConvert</returns>
        private static BitmapEncoder GetImageFromControl(FrameworkElement controlToConvert, ImageType imageType)
        {

            var bounds = controlToConvert.GetBounds(controlToConvert.Parent as Visual);

            var renderBitmap = new RenderTargetBitmap((Int32)bounds.Width, (Int32)bounds.Height, 96d,
                                                      96d, PixelFormats.Pbgra32);
            renderBitmap.Render(controlToConvert);

            BitmapEncoder encoder = GetBitmapEncoderByImageType(imageType);

            // puch rendered bitmap into it
            encoder.Frames.Add(BitmapFrame.Create(renderBitmap));

            return encoder;
        }

        private static Rect GetBounds(this FrameworkElement element, Visual from)
        {
            Rect rect = Rect.Empty;

            try
            {
                GeneralTransform transform = element.TransformToVisual(from);
                rect = transform.TransformBounds(new Rect(0, 0, element.ActualWidth, element.ActualHeight));
                // ReSharper disable EmptyGeneralCatchClause
            }
            catch
            // ReSharper restore EmptyGeneralCatchClause
            {

            }

            return rect;
        }

        /// <summary>
        /// Get an encoder by a specify image type
        /// </summary>
        /// <param name="type">the image type</param>
        /// <returns>return an eccoder</returns>
        private static BitmapEncoder GetBitmapEncoderByImageType(ImageType type)
        {
            switch (type)
            {
                case ImageType.Bmp:
                    return new BmpBitmapEncoder();
                case ImageType.Gif:
                    return new GifBitmapEncoder();
                case ImageType.Jpeg:
                    return new JpegBitmapEncoder();
                case ImageType.Png:
                    return new PngBitmapEncoder();
                case ImageType.Tiff:
                    return new TiffBitmapEncoder();
                case ImageType.Wdp:
                    return new WmpBitmapEncoder();
                default:
                    return new PngBitmapEncoder();
            }
        }

        /// <summary>
        /// Get the iamge type by image file name
        /// </summary>
        /// <param name="fileName">the file name of an image</param>
        /// <returns>the iamge type</returns>
        private static ImageType GetImageTypeByFileName(string fileName)
        {
            ImageType returnType = ImageType.Png;

            var extension = Path.GetExtension(fileName);
            if (!String.IsNullOrEmpty(extension))
            {
                switch (extension.ToLower())
                {
                    case ".bmp":
                        returnType = ImageType.Bmp;
                        break;
                    case ".gif":
                        returnType = ImageType.Gif;
                        break;
                    case ".jpeg":
                    case ".jpg":
                    case ".jpe":
                    case "jfif":
                        returnType = ImageType.Jpeg;
                        break;
                    case ".png":
                        returnType = ImageType.Png;
                        break;
                    case ".tiff":
                    case ".tif":
                        returnType = ImageType.Tiff;
                        break;
                    case ".wdp":
                        returnType = ImageType.Wdp;
                        break;
                    default:
                        returnType = ImageType.Png;
                        break;
                }
            }

            return returnType;
        }

        /// <summary>
        /// Get an ImageSource of a control
        /// </summary>
        /// <param name="controlToConvert">The control to convert to an ImageSource</param>
        /// <param name="imageType">the image type</param>
        /// <returns>The returned ImageSource of the controlToConvert</returns>
        public static BitmapSource GetImageOfControl(FrameworkElement controlToConvert, ImageType imageType)
        {
            // return first frame of image 
            var encoder = GetImageFromControl(controlToConvert, imageType);
            if (encoder != null && encoder.Frames != null && encoder.Frames.Count > 0)
            {
                return encoder.Frames[0];
            }

            return new BitmapImage();
        }

        /// <summary>
        /// Get an ImageSource of a control(Jpeg as default type)
        /// </summary>
        /// <param name="controlToConvert">The control to convert to an ImageSource</param>
        /// <returns>The returned ImageSource of the controlToConvert</returns>
        public static BitmapSource GetImageOfControl(FrameworkElement controlToConvert)
        {
            return GetImageOfControl(controlToConvert, ImageType.Jpeg);
        }

        /// <summary>
        /// Save an image of a control
        /// </summary>
        /// <param name="controlToConvert">The control to convert to an ImageSource</param>
        /// <param name="fileName">The location to save the image to</param>
        /// <returns>The returned ImageSource of the controlToConvert</returns>
        public static Boolean SaveImageOfControl(FrameworkElement controlToConvert, String fileName)
        {
            try
            {
                var imageType = GetImageTypeByFileName(fileName);

                using (var outStream = new FileStream(fileName, FileMode.Create))
                {
                    var encoder = GetImageFromControl(controlToConvert, imageType);
                    encoder.Save(outStream);
                }
            }
            catch (Exception e)
            {
#if DEBUG
                Console.WriteLine("Exception caught saving stream: {0}", e.Message);
#endif
                return false;
            }

            return true;
        }

    }

注意到上面的GetImageOfControl方法返回的实际是BitmapFrame, 其是BitmapSource的一种，如果你更习惯使用BitmapImage的话，免费赠送如下方法：

        public static BitmapImage ToBitmapImage(this BitmapSource bitmapSource)
        {
            var encoder = new JpegBitmapEncoder();
            var memoryStream = new MemoryStream();

            encoder.Frames.Add(BitmapFrame.Create(bitmapSource));
            encoder.Save(memoryStream);

            var bmp = new BitmapImage();

            bmp.BeginInit();
            bmp.StreamSource = new MemoryStream(memoryStream.ToArray());
            bmp.EndInit();

            memoryStream.Flush();
            memoryStream.Close();

            return bmp;
        }