矩形几何与相对尺寸…如何?

你可以用一个 MultiBinding 和一个新的 IMultiValueConverter :

public class RectangleConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
        // you can pass in the value to divide by if you want
        return new Rect(0, 0, (double)values[0], (double)values[1] / 3.33);
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
    {
        throw new NotSupportedException();
    }
}

<lcl:RectangleConverter x:Key="rectConverter" />

...

<RectangleGeometry>
    <RectangleGeometry.Rect>
        <MultiBinding Converter="{StaticResource rectConverter}">
            <Binding Path="ActualWidth" RelativeSource="{RelativeSource AncestorType={x:Type Button}}" />
            <Binding Path="ActualHeight" RelativeSource="{RelativeSource AncestorType={x:Type Button}}" />
        </MultiBinding>
    </RectangleGeometry.Rect>
</RectangleGeometry>