StreamGeometry is a light-weight alternative to the PathGeometry class for
creating complex geometric shapes. You can use StreamGeometry when you
need to describe a complex geometry but don’t want the overhead of supporting
data binding, animation, and modification.
There are two classes in WPF that provide the mini-language for describing
geometric paths: StreamGeometry, and PathFigureCollection. You need to use
the StreamGeometry mini-language when you set a property of the Geometry
type, such as the Data property of a Path element.
<path stroke="Blue" data="M 100 120 L 200 120 L 200 220 L 100 170">
This path uses a sequence of four commands. The first command, M, creates the
PathFigure and sets the starting point to (100, 120). The following three
commands (L) create line segments.
See also Mini-Language in MSDN
From the book of Practical WPF Graphics Programming
L endPoint : The end point of the line.
H x : The x-coordinate of the end point of the line.
V y : The y-coordinate of the end point of the line.
F0 specifies the EvenOdd fill rule.
F1 specifies the Nonzero fill rule.
An uppercase M indicates that startPoint is an absolute value; a lowercase m indicates that startPoint is an offset to the previous point
C controlPoint1 controlPoint2 endPoint : Cubic Bezier Curve Command
A size rotationAngle isLargeArcFlag sweepDirectionFlag endPoint : Creates an elliptical arc between the current point and the specified end point.
Z : Ends the current figure and creates a line that connects the current point to the starting point of the figure.