class Arrow(Polygon):
    """
    An arrow patch
    """
    def __init__( self, x, y, dx, dy, width=1.0, arrowstyle='solid', **kwargs ):
        """Draws an arrow, starting at (x,y), direction and length
        given by (dx,dy) the width of the arrow is scaled by width.
        arrowstyle may be 'solid' or 'barbed'
        """
        L = math.hypot(dx,dy) or 1 # account for div by zero
        tL = L*0.9
        #~ if width > 5*L:
            #~ width = tL = width/5
        #~ elif width > L:
        if width > L:
            width = tL = L
        v = tL-width
        w = tL-width*0.3
        arrow = {'barbed': array([[0.0, 0.1], [0.0, -0.1], [w, -0.1],
                        [v, -0.7], [tL, 0.0], [v, 0.7], [w, 0.1]]),
                 'solid': array([[-width*0.05, 0.1], [-width*0.05, -0.1], [v, -0.1],
                        [v, -0.5], [tL, 0.0], [v, 0.5], [v, 0.1]])
                }[arrowstyle]
        arrow[:,1] *= width

        cx = float(dx)/L
        sx = float(dy)/L
        M = array( [ [ cx, sx],[ -sx, cx ] ] )
        verts = matrixmultiply( arrow, M )+ [x,y]
        Polygon.__init__( self, [ tuple(t) for t in verts ], **kwargs )