最终效果如下：

Xaml代码如下：

<Window x:Class="wpf_win_1.Window3"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="动态文反转" Height="300" Width="300">
<Grid x:Name="gd">

</Grid>
</Window>

后台代码如下：

public Window3()
{
InitializeComponent();
Init();
}

void Init()
{
TextBox txtBox = new TextBox()
{
Margin = new Thickness(50,10,49,0),
Height = 50,
Width = 180,
FontSize = 30
};

ScaleTransform st = new ScaleTransform() { ScaleX = 1,ScaleY = -1 };
TranslateTransform tt = new TranslateTransform() { Y = 1 };
TransformGroup tg = new TransformGroup();
tg.Children.Add(st);
tg.Children.Add(tt);

VisualBrush vb = new VisualBrush() { RelativeTransform = tg };
vb.Visual = txtBox;

Rectangle rectangle = new Rectangle()
{
Margin = new Thickness(50,110,
Width = 180
};

rectangle.Fill = vb;

this.gd.Children.Add(txtBox); this.gd.Children.Add(rectangle); }