func (self *Surface) RelLineTo(dx, dy float64) {
C.cairo_rel_line_to(self.context, C.double(dx), C.double(dy))
}
//RelLineTo is a relative-coordinate version of LineTo.
//The point v is considered a vector with the origin at the current point.
//
//If there is no current point, c is now in an error state.
//
//It is equivalent to
// if p, ok := c.CurrentPoint(); ok {
// c.LineTo(p.Add(v))
// } else {
// // c is broken now
// }
//
//Originally cairo_rel_line_to.
func (c *Context) RelLineTo(v Point) *Context {
x, y := v.c()
C.cairo_rel_line_to(c.c, x, y)
return c
}