ContentControl + RenderTargetBitmap + empty image

Question

Im trying to create some chart images without ever displaying those charts on the screen. I'v been at this for quite a while and tried a lot of different things but nothing seems to work. The code works perfectly if I display the chart in a window first, but if I don't display it in a window, the bitmap is just white with a black border (no idea why).

I have tried adding the chart to a border before rendering and giving the border a green borderBrush. In the bitmap, I see the green borderBrush then the black border and white background but no chart. The Chart is not contained in a black boarder so I don't know where that is coming from.

I have tried adding the chart to a window without calling window.Show() and again I just get the black boarder and white background. However if I call window.Show() the bitmap contains the chart.

I have tried using a drawingVisual as explained here, same result.

Here is the code (not including adding the element to a border or window):

private static BitmapSource CreateElementScreenshot(FrameworkElement element, int dpi)
{
    if (!element.IsMeasureValid)
    {
        Size size = new Size(element.Width, element.Height);
        element.Measure(size);
        element.Arrange(new Rect(size));
    }

    element.UpdateLayout();

    var scale = dpi/96.0;

    var renderTargetBitmap = new RenderTargetBitmap
        (
            (int)(scale * element.RenderSize.Width),(int)(scale * element.RenderSize.Height),dpi,dpi,PixelFormats.Default
        );

    // this is waiting for dispatcher to perform measure, arrange and render passes
    element.Dispatcher.Invoke(((Action)(() => renderTargetBitmap.Render(element))), DispatcherPriority.Render);

    return renderTargetBitmap;
}

Note: The chart is a ContentControl.

Is there anyway I can get the chart to render without displaying it in a window first?

Answer 1

Calling element.ApplyTemplate() did the trick.