How to save Canvas-Control at specific position (in a viewbox) to a png in c# wpf?

Question

I want to develope a .NET application with WPF.

In the end there should be a Viewbox or something similar, this Viewbox should contain a canvas and in this canvas there could be various things like filled rectangles, ellipses etc. ( like a drawing application eg. paint).

Now I want to implement the functionallity to save the content of the Canvas to a PNG. I tried rendering the Canvas to a RenderTargetBitmap and then saving it.

The problem here is that I am not able to set specific coordinates, the only thing I can set is the Size (Canvas width & height) of the RenderTargetBitmap, but it will start rendering the Size starting from (0|0) where my Canvas element starts somewhere else. Is there some work arround for that??

The next Problem is, there should be the posibilty to add pictures as sub-element of the root-Canvas, but how could I care about quality and that everything in the Viewbox is printed?

Thank you very much!



------ EDIT ------

I think I've got a Solution:

void SaveUsingEncoder(Canvas myCanvas, string fileName)
    {
        PngBitmapEncoder encoder = new PngBitmapEncoder();
        RenderTargetBitmap bitmap = new RenderTargetBitmap(
            (int)myCanvas.ActualWidth,
            (int)myCanvas.ActualHeight,
            96,
            96,
            PixelFormats.Pbgra32);

        Rect bounds = VisualTreeHelper.GetDescendantBounds(myCanvas);
        Console.WriteLine(bounds.X + "|" + bounds.Y + "  " + bounds.Width + "|" + bounds.Height);
        DrawingVisual dv = new DrawingVisual();
        using (DrawingContext ctx = dv.RenderOpen())
        {
            VisualBrush vb = new VisualBrush(myCanvas);
            ctx.DrawRectangle(vb, null, new Rect(bounds.Location, bounds.Size));
        }
        bitmap.Render(dv);
        BitmapFrame frame = BitmapFrame.Create(bitmap);
        encoder.Frames.Add(frame);
        using (var stream = File.Create(fileName))
        {
            encoder.Save(stream);
        }
    }

This saves the complete canvas for me

Answer 1

at specific position -

I think in your case use Margins.