Chart Add-Ins

From OpenOffice.org Wiki

Chart types can also be created by developing components that serve as chart types. Existing chart types can be extended by adding additional shapes or modifying the existing shapes. Alternatively, a chart can be created from scratch. If drawing from scratch, it is an empty canvas and all shapes would have to be drawn from scratch.

Chart Add-Ins are actually UNO components, thus, you should be familiar with the chapter Writing UNO Components.