Calculate the ConstantPointCoordinates features for the case of
           a single (callapesed) stroke with pen_down features.

def _features_without_strokes(self, hwr_obj):
        """Calculate the ConstantPointCoordinates features for the case of
           a single (callapesed) stroke with pen_down features."""
        x = []
        for point in hwr_obj.get_pointlist()[0]:
            if len(x) >= 3*self.points_per_stroke or \
               (len(x) >= 2*self.points_per_stroke and not self.pen_down):
                break
            x.append(point['x'])
            x.append(point['y'])
            if self.pen_down:
                if 'pen_down' not in point:
                    logging.error("The "
                                  "ConstantPointCoordinates(strokes=0) "
                                  "feature should only be used after "
                                  "SpaceEvenly preprocessing step.")
                else:
                    x.append(int(point['pen_down']))
        if self.pen_down:
            while len(x) != 3*self.points_per_stroke:
                x.append(self.fill_empty_with)
        else:
            while len(x) != 2*self.points_per_stroke:
                x.append(self.fill_empty_with)
        return x