Talk:Link to BLine

In an IRC discussion it was suggested that it should to be possible to:

Provide an easy way for the user to attach a vertex of a bline to another bline

but without the need to create a new vertex over that bline. That allows the simplification of the animation of complex compositions due to the use of less vertices.

See Yoyobuae's example:

bline attached

In that example there are some vertices converted to "BLine Vertex" and some tangents converted to "BLine Tangent". Manipulating the exported parameter that represents 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.

Currently it is done through various export/connect manipulations.

Suggestion: It's desired that this attachment be achieved visually, by using the mouse and context menus. The current method requires the use of exported values and parameter linking, which is less intuitive and also is slower.

Possible realization way:

1. Select the duck you want to link to bline. It could be
   1. bline vertex duck
   2. bline tangent duck
   3. or real duck
2. Right click on the bline (not the bline vertex!)
3. Link
   1. Linking creating appropriate convert sequences.
   2. if selected vertex duck, it placed on bline at position where clicked
   3. if selected tangent duck, it links with bline tangent at click position
      1. Which one of two? Maybe both? --Zelgadis 12:27, 3 March 2008 (EST)
         1. Maybe we want to link our tangent to 90 degrees away from the bline's tangent at the clicked position. The "BLine Tangent" ValueNode can be extended to include an "Offset" parameter. -- dooglus 18:44, 5 March 2008 (EST)
      2. We need to scale tangents as in example above
         1. As of r1856 that is no longer necessary -- dooglus 18:44, 5 March 2008 (EST)
   4. if selected real duck, it links with bline width at click position
      1. currently width value at specific point of bline couldn't be easily retrieved via export/convert combinations --Zelgadis 12:27, 3 March 2008 (EST)
         1. Convert#BLine_Width -- dooglus 18:44, 5 March 2008 (EST)
4. If was more than one duck selected for linking (i.e. bline vertex duck and bline tangent duck) then the Amount values (in "Bline Vertex"/"Bline Tangent" converts) must be linked to ensure that they retrieved from the same position on a bline (if changed).

Inverse Duck Manipulation

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.