'Configure polygonitem polyitem according to provided
arguments:
coordlist is sequence of coordinates
fill is filling color
outline is outline color
top is a boolean value, which specifies if polyitem
will be put on top of the canvas\' displaylist so it
will not be covered by other items.'

def _drawpoly(self, polyitem, coordlist, fill=None, outline=None, width=None, top=False):

    cl = []
    for (x, y) in coordlist:
        cl.append((x * self.xscale))
        cl.append(((- y) * self.yscale))
    self.cv.coords(polyitem, *cl)
    if (fill is not None):
        self.cv.itemconfigure(polyitem, fill=fill)
    if (outline is not None):
        self.cv.itemconfigure(polyitem, outline=outline)
    if (width is not None):
        self.cv.itemconfigure(polyitem, width=width)
    if top:
        self.cv.tag_raise(polyitem)
