# Talk:Link to BLine

By a discussion at the IRC channel it has been requested to be possible to:

1) Attach a vertex of a bline to another bline but without the need of create a new vertex over that bline. That allow simplify the animation of complex compositions due to it needs less vertices.

See Yoyoubae example:

In that example there are some vertices converted to Bline vertex and some tangents converted to Bline tangents. Manipulating the exported parameter that represent the position of the vertex along the curve it is possible to easily modify the shape of the composition allowing a better morphing of the shapes created.

2) Derived from that request it appears the need to be able to manipulate the ducks that have been converted to a composition. That is: inverse manipulation of valuenodes. For the moment there are some convert types that allow inverse manipulation and only for certain parameters. For example tangents allow inverse manipulation (you modify the x/y position and it calculates the r,theta values. It is know that inverse manipulation leads on some inconsistencies. If the the function that convert a type into other is not biunivocal then it can produce undesired results form the point of view of the final user. For example, the Scale convert type would not have any inconsistency due to it has a easy computable reverse function (the reciprocal)

Considering that and taking account that inverse calculation of valuenodes based on ducks position could need some extra computation, it would be good if some convert types can have inverse manipulation.

The proposal is that BLine Vertex converted types allow inverse manipulation. So, manipulating a vertex duck you move the attached vertex along the bline and also match the tangent of the attached vertex to the bline's tangent at that position.