Render individual arc.

        x_start (int): X-coordinate of arrow start point.
        y (int): Y-coordinate of arrow start and end point.
        y_curve (int): Y-corrdinate of Cubic Bézier y_curve point.
        x_end (int): X-coordinate of arrow end point.
        RETURNS (unicode): Definition of the arc path ('d' attribute).

def get_arc(self, x_start, y, y_curve, x_end):
        """Render individual arc.

        x_start (int): X-coordinate of arrow start point.
        y (int): Y-coordinate of arrow start and end point.
        y_curve (int): Y-corrdinate of Cubic Bézier y_curve point.
        x_end (int): X-coordinate of arrow end point.
        RETURNS (unicode): Definition of the arc path ('d' attribute).
        """
        template = "M{x},{y} C{x},{c} {e},{c} {e},{y}"
        if self.compact:
            template = "M{x},{y} {x},{c} {e},{c} {e},{y}"
        return template.format(x=x_start, y=y, c=y_curve, e=x_end)