The way synfig works is a bit special.
Synfig defines its layers using vectors but when a layer is passed to other layer to perform a transformation it is passed on a raster form. It is good and bad at the same time. It is good because it allows transformations for the rendered results of the layers and a great set of effects can be done this way. It is bad because the time to perform the effect increases a lot because the data is in a raster form, not in a vector form.
When you use the rotate layer to rotate something, you effectively rotate the raster output and each layer is still rendered on its own local system.
Although you see the origin of the circle rotate (as well as the radius duck) it is made by an internal transformation (rotate, scale, translate) via the Transform Stack call. It is not accessible using the information in the sif file because it is done internally.
There are transformations that are not possible to be translated to ducks. For example the noise distort layer can’t pass its transformation to the ducks of the transformed layers.
On the other hand, Synfig has a very powerful value node system that allows to you perform complex movements using the Value Node Convert feature.
For instance if you want to see the origin of the layer effectively have the rotated value you have to do this:
- Convert the Origin to Composite. It would give you the x and y components of the Origin.
- Convert the X (Y) component to Cosine (Sine) type.
- Link the provided Angle sub parameter to a angle duck (for instance a star layer)
More complex convert types can be done and they can perform lots of geometrical transformations. See ‘Convert’ at the wiki (ugh, it is down now!).
This won’t give you the numbers of the X and Y positions of the circle’s origin on the sif file because Synfig will only store the formula on the sif file.
In the future, it could be coded another output format for the animation that can be called “raw data”. It could be the current frame vs value for each exported value node, so the Synfig engine can be used as input for other applications.
If you are very interested on this and I have time I could try to code that kind of special export format. It is not a two lines patch but it might be interesting for Synfig’s integration in the animator / game creator tool-chain.