WPF - How can I make a brush that paints graph-paper-like squares?

from http://msdn.microsoft.com/en-us/library/aa480159.aspx

<DrawingBrush Viewport="0,0,10,10"               ViewportUnits="Absolute"              TileMode="Tile">  <DrawingBrush.Drawing>    <DrawingGroup>      <GeometryDrawing Geometry="M0,0 L1,0 1,0.1, 0,0.1Z" Brush="Green" />      <GeometryDrawing Geometry="M0,0 L0,1 0.1,1, 0.1,0Z" Brush="Green" />    </DrawingGroup>  </DrawingBrush.Drawing></DrawingBrush>

Use a DrawingBrush. A Drawing can contain shapes, images, text, and media.

The following example uses a DrawingBrush to paint the Fill of a Rectangle.

Rectangle exampleRectangle = new Rectangle();exampleRectangle.Width = 75;exampleRectangle.Height = 75;// Create a DrawingBrush and use it to// paint the rectangle.DrawingBrush myBrush = new DrawingBrush();GeometryDrawing backgroundSquare =    new GeometryDrawing(        Brushes.White,        null,        new RectangleGeometry(new Rect(0, 0, 100, 100)));GeometryGroup aGeometryGroup = new GeometryGroup();aGeometryGroup.Children.Add(new RectangleGeometry(new Rect(0, 0, 50, 50)));aGeometryGroup.Children.Add(new RectangleGeometry(new Rect(50, 50, 50, 50)));LinearGradientBrush checkerBrush = new LinearGradientBrush();checkerBrush.GradientStops.Add(new GradientStop(Colors.Black, 0.0));checkerBrush.GradientStops.Add(new GradientStop(Colors.Gray, 1.0));GeometryDrawing checkers = new GeometryDrawing(checkerBrush, null, aGeometryGroup);DrawingGroup checkersDrawingGroup = new DrawingGroup();checkersDrawingGroup.Children.Add(backgroundSquare);checkersDrawingGroup.Children.Add(checkers);myBrush.Drawing = checkersDrawingGroup;myBrush.Viewport = new Rect(0, 0, 0.25, 0.25);myBrush.TileMode = TileMode.Tile;exampleRectangle.Fill = myBrush;

Source: MSDN: WPF Brushes Overview

You can do this in XAML using a VisualBrush. As a sample to give you a starting point, here is a blog post that uses VisualBrush to create a hatched brush. It's very close to a grid - and would be fairly easy to convert across.