Returns visible area

        Format is a tuple of the top left tuple and the lower right tuple

def get_visible_area(self):
        """Returns visible area

        Format is a tuple of the top left tuple and the lower right tuple

        """

        grid = self.grid

        top = grid.YToRow(grid.GetViewStart()[1] * grid.ScrollLineX)
        left = grid.XToCol(grid.GetViewStart()[0] * grid.ScrollLineY)

        # Now start at top left for determining the bottom right visible cell

        bottom, right = top, left

        while grid.IsVisible(bottom, left, wholeCellVisible=False):
            bottom += 1

        while grid.IsVisible(top, right, wholeCellVisible=False):
            right += 1

        # The derived lower right cell is *NOT* visible

        bottom -= 1
        right -= 1

        return (top, left), (bottom, right)