WPF Visualbrush to Imagesource

WPF Visualbrush to Imagesource

I would like to save a VisualBrush to a file. I've tried many different
solutions but nothing worked. I've tried to write a simple Converter:
public class BrushToImageSourceConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter,
System.Globalization.CultureInfo culture)
{
if (value is Brush)
{
var brush = (Brush)value;
Size size = new Size(1000, 1000);
if (parameter is Size)
size = (Size)parameter;
RenderTargetBitmap bitmap = new
RenderTargetBitmap((int)size.Width, (int)size.Height, 96, 96,
PixelFormats.Pbgra32);
if (brush is VisualBrush)
{
bitmap.Render(((VisualBrush)brush).Visual);
}
else
{
var drawingVisual = new DrawingVisual();
using (DrawingContext context = drawingVisual.RenderOpen())
{
context.DrawRectangle(brush, null, new Rect(0, 0,
bitmap.Width, bitmap.Height));
}
bitmap.Render(drawingVisual);
}
PngBitmapEncoder encoder = new PngBitmapEncoder();
encoder.Frames.Add(BitmapFrame.Create(bitmap));
encoder.Save(File.OpenWrite(ViewModel.MainViewModel.Random.Next().ToString()
+ ".png"));
return (ImageSource)bitmap;
}
return null;
}
public object ConvertBack(object value, Type targetType, object
parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
All in all the result is a black image. But if I change the source brush
to something like Brushes.Red, the result is a red image. So I would guess
that the rendering to the bitmap fails, but the saveing to a file works.
Does anyone has an idea what I am doing wrong?