This clipping is interpreted in the view coordinate systems,
i.e. subject to the view transform before mapping to the
device coordinate space.
Specifying an empty interface denotes no clipping,
i.e. everything rendered to the canvas will be visible
(subject to device-dependent constraints, of
course). Specifying an empty XPolyPolygon2D, i.e. a
poly-polygon containing zero polygons, or an XPolyPolygon2D
with any number of empty sub-polygons, denotes the NULL
clip. That means, nothing rendered to the canvas will be
visible.
