// Draw text with a border of segments.
private void DrawTextWithBorder(string text,
Point3D ll, Point3D lr, Point3D ur, Point3D ul,
Brush bgBrush, Brush fgBrush,
TextAlignment textAlign, FontFamily fontFamily = null)
{
MeshGeometry3D mesh1 = new MeshGeometry3D();
MainGroup.Children.Add(mesh1.AddFittedText(text,
ll, lr, ur, ul,
bgBrush, fgBrush, textAlign, fontFamily));
MeshGeometry3D mesh2 = new MeshGeometry3D();
HashSet <Edge> edges = new HashSet <Edge>();
mesh2.AddPolygon(edges, 0.01, ll, lr, ur, ul);
MainGroup.Children.Add(mesh2.MakeModel(Brushes.Red));
}