Force rendering of a WPF control in memory

Question

I have the following code:

void Test()
{
    currentImage.Source = GetBitmap();
    RenderTargetBitmap rtb = new RenderTargetBitmap(100, 100, 96.0, 96.0, PixelFormats.Default);
    rtb.Render(currentImage);
}

This code is supposed to render currentImage, which is an Image control in my xaml to a RenderTargetBitmap.

It doesn't work, rtb returns a blank image, the problem is currentImage didn't render itself yet and so this behavior is expected, I think...

To workaround this problem, I wrote this code:

void Test()
{
    currentImage.Source = GetBitmap();

    this.Dispatcher.BeginInvoke((Action)delegate()
    {
        RenderTargetBitmap rtb = new RenderTargetBitmap(100, 100, 96.0, 96.0, PixelFormats.Default);
        rtb.Render(currentImage);
    }, System.Windows.Threading.DispatcherPriority.Render, null);

}

Basically, I wait for currentImage to be rendered and then I can get it properly rendered to my RenderTargetBitmap.

Is there any way to make it work without using this workaround? Force the Image control to render in memory maybe?

thanks!

Answer 1

use a ViewBox to render in memory

Grid grid = new System.Windows.Controls.Grid() { Background = Brushes.Blue, Width = 200, Height = 200 };
Viewbox viewbox = new Viewbox();
viewbox.Child = grid; //control to render
viewbox.Measure(new System.Windows.Size(200, 200));
viewbox.Arrange(new Rect(0, 0, 200, 200));
viewbox.UpdateLayout();
RenderTargetBitmap render = new RenderTargetBitmap(200, 200, 150, 150, PixelFormats.Pbgra32);
render.Render(viewbox);