Doubts about "link to a spline"


I’m writing a short introduction to Synfig for my students (in Spanish), but I want them to be able to make a PNG follow a path. What I have found in the Web is somehow good, but somehow a mess too. In the end, I have to link two properties of my imported PNG (well, of the Switch Layer that’s automatically created around it) to the spline path: Transformation Offset and Transformation Angle.

The simplest sequence that, through experimentation, I have found to accomplish this:

  1. Select both the SWITCH LAYER and the OUTLINE LAYER (in any order).
  2. Click ANY handle in the SWITCH LAYER.
  3. Right-click ANY point on the OUTLINE LAYER and choose LINK TO A SPLINE.

After that, if I look at the TOffset and TAngle SWITCH LAYER properties, I’ll find them CONNECTED to a Spline Vertex & a Spline Tangent respectively. Moreover, I can DISCONNECT the TAngle from the Spline Tangent & keep the positional link while freeing the PNG orientation.

My questions are:

  1. Do I need to use handles? Isn’t there a way to do it from the Parameters Panel?
  2. Can’t I directly link just the TOffset to a spline? Must I always link TAngle too, then disconnect it later?
  3. Why do additional ROTATE LAYERS appear in some tutorials about making an arrow follow a spline?
  4. Why is there a SWITCH LAYER around each IMPORT IMAGE LAYER instead of, for instance, a GROUP one?


Hello, I see you talk spanish. I’m going to write my opinion in spanish, because it’s easier for me to express what I think:

1.- Creo que es mas fácil hacerlo usando “handles”, que usando parámetros. En ciertas ocasiones, se tiene que hacer una transformación de tipo para poder enlazar parámetros en distintas capas

2.- Al momento de responderle, no tengo abierto synfig. Pero me parece que si es posible. Se puede ir acumulando la selección de “handles”, presionando CTRL y haciendo click derecho, si mal no me acuerdo. Pero cuando no se seleciona el ángulo, la imagen PNG no “girará” cuando el camino cambie de dirección.

3.- Eso a de ser porque se trata de tutoriales antiguos. Antes la Capa de Grupos no tenía parámetros de transformaciones geométricas (girar, escalar, etc). La capa “Switch” ni siquiera existía. Sin embargo, esos tutoriales aún pueden ser útiles. Tendría que verlos para poder tener mas alcances sobre eso.

4.- Fue una decisión de los desarrolladores. Pero me parece que el origen fue por el pedido de muchos usuarios de hacer una animación “cuadro por cuadro” o una animación “de diapositivas”. No estoy seguro, pero creo que se puede mover la capa imágen, a una capa grupo, pero se podría armar un desbarajuste :laughing: .

[size=85]Nisiquiera en español puedo evitar las faltas ortográficas, y expresarme como salvaje! [/size]


Hi, Hulf2012!

Thanks for your answer. I feel much more comfortable in Spanish too, but I’m going to try to keep on using English in order to get help from non-Spanish-speakers too, if possible.

  1. If the transformations are automatically carried out by Synfig Studio when handles are selected, it could carry them out too if the corresponding parameters were selected instead. I suppose.

  2. The PNG angle gets linked to the spline tangent no matter whether the rotation handle is selected or not. If you try it and conclude otherwise, please let me know.

3 & 4. Thanks for the historical info. :slight_smile:



1.- I don’t understand what is your point. When I say transformation, maybe it’s better to say change, or casting… of type of variables :question: . In Programming is similar to change a “string” variable to a “integer” variable, or a “boolean” variable. And it’s not easy for a computer to guess what kind of “type” cast the user wants…, it’s not so easy to program. Synfig can do this transformation as an special feature, as a help for users. It seems that there is no other “simple” way. I could say it’s a defect: there is no obvious way to do it. Your students will have to memorize it. I’m talking only about the “object which follows a path” command … well, It’s my opinion. I’m also here to learn.

2.- I’ve tried and you are right. But Other users could know how to do it.

Let’s see what other users have to say


Well, more about 1:
1.- I’ve done some tests with a circle layer, and a outline layer as a pathway
2.- I’ve selected the center of the circle parameter, which is a vector
3.- I’ve made the “cast” from vector to spline vertex
4.- Now, I export the list of points parameter, from the oultine layer. I put a name, ovbiously
5.- Then I connect (or link?) the exported list to the center of the circle, which now has a spline vertex type.

Now the circle follows the path

Please do the tests with a Group layer, or with a Switch layer. Your Image layer have to be inside of them. I advise to locate the image and the group layers at the center of the canvas, without any move transformation, or anything.

Yes, you can do it from the parameters panel. If you do so, then you have to select the parameter you want to link to spline (or the sub parameter) and right click and choose Tangent of Spline or Vertex Of spline (one or other depending of the use you’re doing). In that case the spline it is linked to, is a empty spline, so in order to make it work properly, you have to connect that empty spline to the spline you really want to be linked to. Usually you need to export the spline you want to link to, before connect the dummy empty one to it.

No, you can just do it for the TOffset but necessarily need to do it form the parameters panel and doing the steps above explained. The operation made using the handles in the canvas is automatically made for the angle and offset together. That’s the way it has been coded.


Hi, Hulf2012 & Genete!

OK, thanks to you both! So there’s a way for making the links from the Parameters Panel, with detailed control of exactly what things you want to connect (I have checked what you have answered, with an imported PNG & a spline outline), and a shortcut using handles that links both position & angle at once.

Understood! :slight_smile:

Thanks again.