Save content of a visual Object as a image file in WPF? - wpf

Question

I need to save the content of a WPF Object as an Image file. In my application I have a chart drawn on a Canvas object. This is what I need to save. The Canvas with all child objects.

Answer 1

What you're looking for is the RenderTargetBitmap class. There's an example of its use on the MSDN page I linked, and there's another good example that includes saving to a file here:
RenderTargetBitmap by Eric Sinc

Answer 2

Here is the func which creates RenderTargetBitmap object, that will be used in further funcs.
public static RenderTargetBitmap ConvertToBitmap(UIElement uiElement, double resolution)
{
var scale = resolution / 96d;
uiElement.Measure(new Size(Double.PositiveInfinity, Double.PositiveInfinity));
var sz = uiElement.DesiredSize;
var rect = new Rect(sz);
uiElement.Arrange(rect);
var bmp = new RenderTargetBitmap((int)(scale * (rect.Width)), (int)(scale * (rect.Height)), scale * 96, scale * 96, PixelFormats.Default);
bmp.Render(uiElement);
return bmp;
}
This functionc creates JPEG string content of file and writes it to a file:
public static void ConvertToJpeg(UIElement uiElement, string path, double resolution)
{
var jpegString = CreateJpeg(ConvertToBitmap(uiElement, resolution));
if (path != null)
{
try
{
using (var fileStream = File.Create(path))
{
using (var streamWriter = new StreamWriter(fileStream, Encoding.Default))
{
streamWriter.Write(jpegString);
streamWriter.Close();
}
fileStream.Close();
}
}
catch (Exception ex)
{
//TODO: handle exception here
}
}
}
This function used above to create JPEG string representation of Image content:
public static string CreateJpeg(RenderTargetBitmap bitmap)
{
var jpeg = new JpegBitmapEncoder();
jpeg.Frames.Add(BitmapFrame.Create(bitmap));
string result;
using (var memoryStream = new MemoryStream())
{
jpeg.Save(memoryStream);
memoryStream.Seek(0, SeekOrigin.Begin);
using (var streamReader = new StreamReader(memoryStream, Encoding.Default))
{
result = streamReader.ReadToEnd();
streamReader.Close();
}
memoryStream.Close();
}
return result;
}
Hope this helps.

Answer 3

With the help of the Eric Sinc tutorial I came to the following solution:
It uses a win32 SaveDialog to choose where the file should go and a PngBitmapEncoder (many other BitmapEncoders available!) to convert it to something we can save.
Note that the element being saved in this example is "cnvClasses" and that the size of the output is, quite deliberately, the same as the control.
SaveFileDialog svDlg = new SaveFileDialog();
svDlg.Filter = "PNG files|*.png|All Files|*.*";
svDlg.Title = "Save diagram as PNG";
if (svDlg.ShowDialog().Value == true)
{
RenderTargetBitmap render = new RenderTargetBitmap((int)this.cnvClasses.ActualWidth, (int)this.cnvClasses.ActualHeight, 96, 96, PixelFormats.Pbgra32);
render.Render(cnvClasses);
PngBitmapEncoder encoder = new PngBitmapEncoder();
encoder.Frames.Add(BitmapFrame.Create(render));
using (FileStream fs = new FileStream(svDlg.FileName, FileMode.Create))
encoder.Save(fs);
}