I've been playing around with WPF animation, and ended up wanting to take a snapshot of an animation at a specific place.

Specifically, I have a canvas that has some pictures on it that are moving, and I want to be able to save a bitmap of what it looks like at a specific time.

Getting the bitmap is pretty easy, using a RenderTargetBitmap and a VisualBrush.

private BitmapSource CaptureScreen(Visual target)
{

    Rect bounds = VisualTreeHelper.GetDescendantBounds(target);

    RenderTargetBitmap renderBitmap = new RenderTargetBitmap(800, 600, 96, 96, PixelFormats.Pbgra32);

    DrawingVisual dv = new DrawingVisual();
   
using (DrawingContext ctx = dv.RenderOpen())
    {
        
VisualBrush vb = new VisualBrush(target);

        ctx.DrawRectangle(vb, null, new Rect(new Point(), bounds.Size));
    }
    renderBitmap.Render(dv);

    return renderBitmap;
}

That gives you the state of the objects pre-animation, but what I really wanted was the state of the objects during the animation. I had some code to move the image around:

    DoubleAnimation anim = new DoubleAnimation(50, 400, TimeSpan.FromSeconds(10), FillBehavior.HoldEnd);
    AnimationClock clock = anim.CreateClock();
    m_imageLeft.ApplyAnimationClock(
Canvas.LeftProperty, clock);

After a bit of research, I settled on the following bit of code to set the animation to the point that I wanted:

    clock.Controller.SeekAlignedToLastTick(TimeSpan.FromSeconds(5.0), TimeSeekOrigin.BeginTime);

Which should have worked fine, but didn't. When I looked at the properties, I noticed that the Left property was changing, but it wasn't showing up. It was almost as if the Canvas didn't know that the object property had changed and a re-layout was necessary...

    m_canvas.UpdateLayout();

was the magic incantation to make that happen.

(Note that I'm a novice at WPF, and there may be a better way to do this...)