Question

I’ve got an app that turns some XAML Usercontrols into PNGs – this has worked really well up to now, unfortunately I now need to double the size of the images.

My method (that doesn’t work!) was to add a ScaleTransform to the visual element after I’ve loaded it …

This line is the new line at the top of the SaveUsingEncoder method.

visual.RenderTransform = GetScaleTransform(2);

The PNG is the new size (3000 x 2000) – but the XAML is Rendered at 1500×1000 in the centre of the image.

Can anyone assist please?

    private void Load(string filename)
    {
        var stream = new FileStream(filename), FileMode.Open);
        var frameworkElement = (FrameworkElement)(XamlReader.Load(stream));

        var scale = 2;

        var encoder = new PngBitmapEncoder();
        var availableSize = new Size(1500 * scale, 1000 * scale);

        frameworkElement.Measure(availableSize);
        frameworkElement.Arrange(new Rect(availableSize));
        name = name.Replace(" ", "-");
        SaveUsingEncoder(frameworkElement, string.Format(@"{0}.png", name), encoder, availableSize);
    }

    private TransformGroup GetScaleTransform(int scale)
    {
        var myScaleTransform = new ScaleTransform {ScaleY = scale, ScaleX = scale};
        var myTransformGroup = new TransformGroup();
        myTransformGroup.Children.Add(myScaleTransform);
        return myTransformGroup;
    }

    private void SaveUsingEncoder(FrameworkElement visual, string fileName, BitmapEncoder encoder, Size size)
    {
        visual.RenderTransform = GetScaleTransform(2);
        var bitmap = new RenderTargetBitmap(
            (int) size.Width,
            (int) size.Height,
            96,
            96,
            PixelFormats.Pbgra32);
        bitmap.Render(visual);

        var frame = BitmapFrame.Create(bitmap);
        encoder.Frames.Add(frame);

        using (var stream = File.Create(fileName))
        {
            encoder.Save(stream);
        }
    }

Answer 1

Called visual.UpdateLayout before rendering into the RenderTargetBitmap

(Thanks to Clemens for this answer – but he put it as a comment!)