Question

How do I bind something to a fraction of a Path value? Path=ActualPath/2 does not seem to work.

Height="{Binding RelativeSource={RelativeSource AncestorType={x:Type UserControl}}, 
                   Path=ActualHeight / 2}">

Answer 1

You can do that using a ValueConverter, for example:

class MakeHalfConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return ((double)value)/2;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return ((double)value)*2;
    }
}