Rebuilds the item based on the current points.

def rebuild( self ):
        """
        Rebuilds the item based on the current points.
        """
        scene       = self.scene()
        if not scene:
            return
        
        self._subpaths = []
        
        grid        = scene.gridRect()
        typ         = self.chartType()
        
        hruler      = scene.horizontalRuler()
        vruler      = scene.verticalRuler()
        
        path        = QPainterPath()
        area        = QPainterPath()
        
        self._buildData.clear()
        self._buildData['path_area'] = area
        
        self.setPos(0, 0)
        
        # draw a line item
        if typ == XChartScene.Type.Line:
            first = True
            pos   = None
            home  = None
            self._ellipses = []
            
            points = self.points()
            if ( self.orientation() == Qt.Horizontal ):
                points.sort(hruler.compareValues, key = lambda x: x[0])
            else:
                points.sort(vruler.compareValues, key = lambda y: y[1])
                points.reverse()
            
            for x, y in self.points():
                pos = scene.mapFromChart(x, y)
                if first:
                    home = QPointF(pos.x(), grid.bottom())
                    area.moveTo(home)
                    area.lineTo(pos)
                    path.moveTo(pos)
                    
                    self._ellipses.append(pos)
                    
                    first = False
                else:
                    path.lineTo(pos)
                    area.lineTo(pos)
                    
                    self._ellipses.append(pos)
            
            if pos and home:
                area.lineTo(pos.x(), grid.bottom())
                area.lineTo(home)
        
        # draw a bar item
        elif typ == XChartScene.Type.Bar:
            barsize = self.barSize()
            horiz   = self.orientation() == Qt.Horizontal
            
            for x, y in self.points():
                pos = scene.mapFromChart(x, y)
                subpath = QPainterPath()
                if horiz:
                    r = min(grid.bottom() - pos.y(), 8)
                    
                    subpath.moveTo(pos.x() - barsize / 2.0, grid.bottom())
                    subpath.lineTo(pos.x() - barsize / 2.0, pos.y() + r)
                    subpath.quadTo(pos.x() - barsize / 2.0, pos.y(),
                                   pos.x() - barsize / 2.0 + r, pos.y())
                    
                    subpath.lineTo(pos.x() + barsize / 2.0 - r, pos.y())
                    subpath.quadTo(pos.x() + barsize / 2.0, pos.y(),
                                   pos.x() + barsize / 2.0, pos.y() + r)
                    
                    subpath.lineTo(pos.x() + barsize / 2.0, grid.bottom())
                    subpath.lineTo(pos.x() - barsize / 2.0, grid.bottom())
                else:
                    subpath.moveTo(grid.left(), pos.y() - barsize / 2.0)
                    subpath.lineTo(pos.x(),     pos.y() - barsize / 2.0)
                    subpath.lineTo(pos.x(),     pos.y() + barsize / 2.0)
                    subpath.lineTo(grid.left(), pos.y() + barsize / 2.0)
                    subpath.lineTo(grid.left(), pos.y() - barsize / 2.0)
                
                path.addPath(subpath)
                self._subpaths.append((x, y, subpath))
        
        # draw a pie chart
        elif typ == XChartScene.Type.Pie:
            if self.orientation() == Qt.Horizontal:
                key_index   = 0
                value_index = 1
                value_ruler = self.verticalRuler()
            else:
                key_index   = 1
                value_index = 0
                value_ruler = self.horizontalRuler()
        
            pie_values = {}
            
            for point in self.points():
                key     = point[key_index]
                value   = point[value_index]
                
                pie_values.setdefault(key, [])
                pie_values[key].append(value)
        
            for key, values in pie_values.items():
                pie_values[key] = value_ruler.calcTotal(values)
            
            total = max(1, value_ruler.calcTotal(pie_values.values()))
            
            # calculate drawing parameters
            center   = self.pieCenter()
            radius   = self.radius()
            diameter = radius * 2
            angle    = 0
            bound    = QRectF(-radius, -radius, diameter, diameter)
            
            for key, value in sorted(pie_values.items(), key = lambda x: x[1]):
                # calculate the percentage
                perc  = float(value) / total
                
                # calculate the angle as the perc * 360
                item_angle = perc * 360
                self.setPos(center)
                
                sub_path = QPainterPath()
                sub_path.arcTo(bound, angle, item_angle)
                sub_path.lineTo(0, 0)
                
                path.addPath(sub_path)
                self._subpaths.append((key, value, sub_path))
                
                angle += item_angle
                
        self.setPath(path)
        self._dirty = False