Preventing deformation in XAML Grid's background when resizing - wpf

Question

I am writing a brush in XAML that I can use to paint the background of a Grid to create a banner. It looks like this:
I want the brush to "stretch" with the Grid when the Window resizes, but I do not want the center angles to deform.
I only need to be able to draw the shapes in the background of a Grid. How can I avoid the deformation?
The code I've written looks like this:
<Window x:Class="WpfApplication.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Height="60" Width="300">
<Window.Resources>
<DrawingBrush x:Key="GridBackground">
<DrawingBrush.Drawing>
<DrawingGroup>
<DrawingGroup.Children>
<GeometryDrawing Geometry="M0,1 0,0 0.4,0 0.45,0.5 0.4,1Z" Brush="#FF6A00" />
<GeometryDrawing Geometry="M0.6,1 0.55,0.5 0.6,0 1,0 1,1Z" Brush="#FF0000" />
</DrawingGroup.Children>
</DrawingGroup>
</DrawingBrush.Drawing>
</DrawingBrush>
</Window.Resources>
<Grid Background="{StaticResource GridBackground}">
<TextBlock Foreground="White" VerticalAlignment="Center">Some text</TextBlock>
</Grid>
</Window>

Answer 1

I would make it two brushes, one anchored to the right, and one anchored to the left. Something like this:
<Grid>
<GeometryXXX Geometry="M0,1 0,0 0.4,0 0.45,0.5 0.4,1Z" Width="300" HorizontalAlignment="Left" Brush="#FF6A00">
<GeometryXXX Geometry="M0,1 0,0 0.4,0 0.45,0.5 0.4,1Z" Width="300" HorizontalAlignment="Right" Brush="#FF0000">
<TextBlock Foreground="White" VerticalAlignment="Center">Some text</TextBlock>
</Grid>
I don't have my compiler open, and I don't remember the name of the Geometry drawing object.
The other way of doing it would be to create a valueconverter, and do something like:
...
<GeometryDrawing Geometry="{Binding Width, ValueConverter=LeftAngledThing}" Brush="#FF6A00" />
<GeometryDrawing Geometry="{Binding Width, ValueConverter=LeftAngledThing}" Brush="#FF0000" />
...
You would need to look up the exact syntax for how to do this though, as I don't remember it right now.