Use CanvasVirtualControl if:

• the image you are drawing is very large
• you don't want to spend time drawing non-visible parts of the image
• you don't want the entire image to be resident in memory
• or you want to control what thread the drawing happens on

From within the RegionsInvalidated event handler, use CreateDrawingSession(Rect) to redraw:

void OnRegionsInvalidated(CanvasVirtualControl sender, CanvasRegionsInvalidatedEventArgs args)
{
    foreach (var region in args.InvalidatedRegions)
    {
        using (var ds = sender.CreateDrawingSession(region))
        {
            // draw the region
        }
    }
}

CanvasVirtualControl works well when it is placed within a XAML ScrollViewer:

<ScrollViewer>
  <canvas:CanvasVirtualControl Width="10000" Height="10000" RegionsInvalidated="OnRegionsInvalidated" />
</ScrollViewer>

When a CanvasVirtualControl's size changes the current contents of the control is not invalidated. In order to make the contents invalidate on resize, add a SizeChanged event handler and call Invalidate() from it:

void VirtualControl_SizeChanged(object sender, SizeChangedEventArgs e)
{
    VirtualControl.Invalidate();
}

Reference