cairo/canvas.go
func (v *Context) Arc(xc, yc, radius, angle1, angle2 float64) {
	C.cairo_arc(v.native(), C.double(xc), C.double(yc), C.double(radius), C.double(angle1), C.double(angle2))
}
func (v *Context) Arc(xc, yc, radius, angle1, angle2 float64) {
	C.cairo_arc(v.native(), C.double(xc), C.double(yc), C.double(radius), C.double(angle1), C.double(angle2))
}
// Arc is a wrapper around cairo_arc().