grid package, except that
they do not call 'L_gridDirty'. This is to enable
mixing base and grid graphics in aheatmap. tryViewportIt uses grid.ls and
not seekViewport as the latter would reset
the graphic device.
grid.Call.graphics(fnname, ...) grid.Call(fnname, ...)
current.vpPath()
tryViewport(name, verbose = FALSE)
grid function name.