Set a clip on an existing viewport
igc_clip(x, clip)viewport or grob with a viewport
One of "on", "inherit", or "off", indicating whether to clip to the extent of this viewport, inherit the clipping region from the parent viewport, or turn clipping off altogether. For back-compatibility, a logical value of TRUE corresponds to "on" and FALSE corresponds to "inherit". May also be a grob (or a gTree) that describes a clipping path.