[cairo] gradient

[young]

Hi all,
    I want to draw an arc on the window by cairo ,the arc is requested 
color gradient.I see some cairo's example,and only finding  the  line 
and the  circle's color gradient.Then I see the API and find 
cairo_pattern_creat_linear()
cairo_pattern_creat_radial()
But there's no API for drawing arc's gradient.
Thanks for any ideas

Young