Get a bitmap from a WPF unshown control

Question

I'd like to create a bitmap from a WPF control. I see some examples in this forum (one above all: Render a "not visible" WPF controls to an bitmap image ), but they can render well only if the WPF control is already shown on the screen.

I have to create a control in a model to associate the bitmap result into an his internal bitmap field.

I followed the example into the above thread, but the result was a bitmap with only a part of the content of the control (as if it was not completely rendered).

How perform a complete render before the image render aquisition?

This is my source code:

if( spChart == null){
    String s = "<SparrowChart xmlns=\"http://sparrowtoolkit.codeplex.com/wpf\">" +
                          "    <SparrowChart.XAxis>" +
                          "        <LinearXAxis/>" +
                          "    </SparrowChart.XAxis>" +
                          "    <SparrowChart.YAxis>" +
                          "        <LinearYAxis/>" +
                          "    </SparrowChart.YAxis>" +
                          "</SparrowChart>";
    System.IO.StringReader stringReader = new System.IO.StringReader(s);
    System.Xml.XmlReader xmlReader;
                xmlReader = System.Xml.XmlReader.Create(stringReader);
    spChart = (Sparrow.Chart.SparrowChart)System.Windows.Markup.XamlReader.Load(xmlReader);
    spChart.XAxes[0].MinValue = 0;
    spChart.XAxes[0].MaxValue = 10;
    spChart.YAxes[0].MinValue = 0;
    spChart.YAxes[0].MaxValue = 10;
    spChart.Series.Clear();
} else {
    spChart.Series.Clear();
}

List<System.Drawing.PointF> points = new List<System.Drawing.PointF> {new System.Drawing.PointF(3, 7),
                                                                      new System.Drawing.PointF(5, 2),
                                                                      new System.Drawing.PointF(8, 4),
                                                                      new System.Drawing.PointF(4, 6)};
Sparrow.Chart.SeriesBase LS = new Sparrow.Chart.SplineSeries();
foreach(System.Drawing.PointF x in points) {
    Sparrow.Chart.DoublePoint newPoint = new Sparrow.Chart.DoublePoint();
    newPoint.Data=x.X;
    newPoint.Value=x.Y;
}
spChart.Series.Add(LS);
LS = new Sparrow.Chart.ScatterSeries();
foreach(System.Drawing.PointF x in points) {
    Sparrow.Chart.DoublePoint newPoint = new Sparrow.Chart.DoublePoint();
    newPoint.Data=x.X;
    newPoint.Value=x.Y;
}
spChart.Series.Add(LS);
spChart.Measure(new System.Windows.Size(Double.PositiveInfinity, Double.PositiveInfinity));
spChart.Arrange(new System.Windows.Rect(new System.Windows.Size(1000, 1000)));
spChart.UpdateLayout();

RenderTargetBitmap rtb = new RenderTargetBitmap((int)SpChart.ActualWidth, (int)SpChart.ActualHeight, 96, 96, Windows.Media.PixelFormats.Pbgra32);
rtb.Render(spChart);
PngBitmapEncoder png = new PngBitmapEncoder();
png.Frames.Add(BitmapFrame.Create(rtb));
MemoryStream stream = New MemoryStream();
png.Save(stream);
Bitmap tmpBitmap = new Bitmap(Image.FromStream(stream));
bitmapToRender = MyBitmap.Clone();
MyBitmap.Dispose();

Thank you

Lucio

Answer 1

For me, this one works:

Size size = new Size(432, 460);
frameworkElement.Measure(size);
frameworkElement.Arrange(new Rect(new Point(), size));
frameworkElement.UpdateLayout();

RenderTargetBitmap renderTargetBitmap = new RenderTargetBitmap((int)frameworkElement.ActualWidth, (int)frameworkElement.ActualHeight, 96, 96, PixelFormats.Pbgra32);
renderTargetBitmap.Render(frameworkElement);

FormatConvertedBitmap monoBitmap = new FormatConvertedBitmap(renderTargetBitmap, PixelFormats.BlackWhite, null, 0);

BmpBitmapEncoder bmpImage = new BmpBitmapEncoder();
bmpImage.Frames.Add(BitmapFrame.Create(monoBitmap));

byte[] bmpData;

using (MemoryStream buffer = new MemoryStream())
{
    bmpImage.Save(buffer);
    bmpData = buffer.ToArray();
}

Sorry for resulting in monochrome bitmap, that's just what I used. This can simply be converted to any bitmap type as a result.