As it stands, the module can only rotate the following object types about their centers:

Lines
Polygons
Rectangles (if rectToPoly(1) is called)
Ovals (if ovalToPoly(1) is called)
All other object types (bitmap, image, arc, text, && window) can only be rotated about another point. A warning is issued if the user tries to rotate one of these object types about their center. Hopefully, more types will be able to center-rotate in the future.