"""Widgets are placed on fixed position as specified in hints.

    Position can be relative to any side or center of parent widget.

        self._widget_hints = {}  # Widget : (left, top, right, bottom, xrel, yrel)

    def add(self, widget, left=None, top=None, right=None, bottom=None,

            center=None, fill=None):

        """Add widget to layout.

        Place hints:

        * left, right, top, bottom = None | <num> ; <num> >= 0

            - Fix Widget position to parent sides.

            - If both left and right (or top and bottom) are set, the widget

              will be stretched to fill full area minus specified space.

        * center, fill = None | 'x' | 'y' | 'xy'

            - Center widget in x, y or both axes.

            - Fill is shortcut for setting both positions in same axis.

        """

        # Internally, coordinate relation is marked as:

        # '+': from left or top

        # '-': from right or bottom

        # 'C': from center

        # 'F': from both sides (fill)

        xrel, yrel = '+', '+'

        fill, center = fill or '', center or ''

        if left is None and right is not None:

            xrel = '-'

        if top is None and bottom is not None:

            yrel = '-'

        if 'x' in center:

            xrel = 'C'

        if 'y' in center:

            yrel = 'C'

        if 'x' in fill:

            xrel = 'F'

        if 'y' in fill:

            yrel = 'F'

        self._widget_hints[widget] = (left or 0, top or 0,

                                      right or 0, bottom or 0,

                                      xrel, yrel)

            left, top, right, bottom, xrel, yrel = self._widget_hints[widget]

            ox, oy = 0, 0  # origin

            if xrel == '-':

                ox = w - sw

            if yrel == '-':

                oy = h - sh

            if xrel == 'C':

                ox = (w - sw) // 2

            if yrel == 'C':

                oy = (h - sh) // 2

            px = ox + left - right

            py = oy + top - bottom

            if xrel == 'F':

                px = left

                sw = w - left - right

            if yrel == 'F':

                py = top

                sh = h - top - bottom