Each node has a Position Panel whose Panel.itemArray is data bound to the "slices" property of the node data. That "slices" property is an Array of data objects; for each item the Panel.itemTemplate produces a Shape whose Shape.geometry is computed using a conversion function to generate a pie-shaped slice given a start angle and a sweep angle from the item data. Note that Shape.isGeometryPositioned is true to make sure all of the Shapes are positioned by their computed geometries, independent of any stroke width. Each slice Panel also has a tooltip showing some information.
For more sophisticated charts within nodes, see the Canvas Charts sample.