func (v *Context) SetDash(dashes []float64, offset float64) {
	header := (*reflect.SliceHeader)(unsafe.Pointer(&dashes))
	cdashes := (*C.double)(unsafe.Pointer(header.Data))
	C.cairo_set_dash(v.native(), cdashes, C.int(header.Len),
		C.double(offset))
}
func (v *Context) SetDash(dashes []float64, offset float64) {
	header := (*reflect.SliceHeader)(unsafe.Pointer(&dashes))
	cdashes := (*C.double)(unsafe.Pointer(header.Data))
	C.cairo_set_dash(v.native(), cdashes, C.int(header.Len),
		C.double(offset))
}
// SetDash is a wrapper around cairo_set_dash().