Programming WPF, 2nd Edition

Shapes

The System.Windows.Shapes namespace defines drawing primitives that act as elements in the user interface tree. WPF supports a variety of different shapes, and provides element types for each of them, which are shown in Table 13-1. These integrate with framework-level functionality such as layout, styling, and data binding. These services are not without their costs, so it's useful to be aware that the shape classes provide a layer of abstraction on top of a lower-level set of services. See the "Shape Objects Versus Geometries" sidebar for details.

Table 13-1. Shapes

Shape Type	Usage
Ellipse	An ellipse
Line	A single straight line
Path	A shape using any mixture of straight lines and curves
Polygon	A closed shape made from straight lines
Polyline	An open shape made from straight lines
Rectangle	A rectangle, optionally with rounded corners

Shape Objects Versus Geometries

A common source of confusion for people learning WPF is that it appears to have two sets of graphical classes. For example, as well as Rectangle, there is RectangleGeometry, and we have Path as well as PathGeometry. Most of the shape classes in the System.Windows.Shapes namespace have corresponding geometry classes in the System.Windows.Media namespace. Although this may seem redundant, the two kinds of classes serve different purposes.

Geometries are just descriptions of shapes. For example, a LineGeometry defines a StartPoint and an EndPoint. A LineGeometry does not know what color it should be. It cannot raise ...