def analyze(self, laparams):
     LTTextGroup.analyze(self, laparams)
     # reorder the objects from top-right to bottom-left.
     self._objs = csort(self._objs, key=lambda obj:
                        -(1+laparams.boxes_flow)*(obj.x0+obj.x1)
                        -(1-laparams.boxes_flow)*(obj.y1))
     return

    def group_textboxes(self, laparams, boxes):
        assert boxes

        def dist(obj1, obj2):
            """A distance function between two TextBoxes.

            Consider the bounding rectangle for obj1 and obj2.
            Return its area less the areas of obj1 and obj2,
            shown as 'www' below. This value may be negative.
                    +------+..........+ (x1, y1)
                    | obj1 |wwwwwwwwww:
                    +------+www+------+
                    :wwwwwwwwww| obj2 |
            (x0, y0) +..........+------+
            """
            x0 = min(obj1.x0, obj2.x0)
            y0 = min(obj1.y0, obj2.y0)
            x1 = max(obj1.x1, obj2.x1)
            y1 = max(obj1.y1, obj2.y1)
            return ((x1-x0)*(y1-y0) - obj1.width*obj1.height - obj2.width*obj2.height)

        def isany(obj1, obj2):
            """Check if there's any other object between obj1 and obj2.
            """
            x0 = min(obj1.x0, obj2.x0)
            y0 = min(obj1.y0, obj2.y0)
            x1 = max(obj1.x1, obj2.x1)
            y1 = max(obj1.y1, obj2.y1)
            objs = set(plane.find((x0, y0, x1, y1)))
            return objs.difference((obj1, obj2))
        
        # XXX this still takes O(n^2)  :(
        dists = []
        for i in xrange(len(boxes)):
            obj1 = boxes[i]
            for j in xrange(i+1, len(boxes)):
                obj2 = boxes[j]
                dists.append((0, dist(obj1, obj2), obj1, obj2))
        # We could use dists.sort(), but it would randomize the test result.
        dists = csort(dists)
        plane = Plane(self.bbox)
        plane.extend(boxes)
        while dists:
            (c, d, obj1, obj2) = dists.pop(0)
            if c == 0 and isany(obj1, obj2):
                dists.append((1, d, obj1, obj2))
                continue
            if (isinstance(obj1, (LTTextBoxVertical, LTTextGroupTBRL)) or
                isinstance(obj2, (LTTextBoxVertical, LTTextGroupTBRL))):
                group = LTTextGroupTBRL([obj1, obj2])
            else:
                group = LTTextGroupLRTB([obj1, obj2])
            plane.remove(obj1)
            plane.remove(obj2)
            dists = [ n for n in dists if (n[2] in plane and n[3] in plane) ]
            for other in plane:
                dists.append((0, dist(group, other), group, other))
            dists = csort(dists)
            plane.add(group)
        assert len(plane) == 1
        return list(plane)