Say I create an object in Inkscape. I then move the vertices and so on until I come up with a new object. Is there a way then to bring both objects into Synfig and tween between them?
Simple answer: No and never can be automatic.
Answer to understand why:
To change one object to other you must explicitly tell to the program what part of the start shape morphs to what part of the end shape. The reason is easy. Give a start and end shapes to two persons and ask them to draw an intermediate shape for their morphing. It is 100% sure that the intermediate shape would be different from the one person to other. Why should the computer would do the way you want to do it?
The solution, morph it yourself. Do you your animation!
I have done this, but it’s very fiddly.
It involves importing both of the shapes, creating two keyframes, exporting the vertices from the first shape and then linking these exported vertices to the vertices of the second shape at the first keyframe, making sure before you do this that you’ve nudged all the vertices of the second shape at both keyframes in Animate Mode to create waypoints so you can get a tween between the two.
You also have to deal with things like having an equal number of vertices in both shapes.
It’s much quicker to only draw the first shape in Inkscape and move the vertices to create the second shape on a new key frame in Synfig itself (or vice versa). This method also means you can do things like switch off vertices you don’t need, so is much more flexible.
Just to show it’s possible, I drew two rectangles in Synfig Studio (“first” and “second”) and then used the corners of “first” as the start point of a tween to that ends with “second”. You can see the exported corners in the Children panel. You should try and create a similar example from scratch before you try doing this with shapes imported from Inkscape.
When I have time I can write a wiki page that details how to do this but it’s usually much faster to only draw either the start or end shape in Inkscape and then animate it into the other shape in Synfig.
tween.sifz (704 Bytes)
This is something that is very commonly done in tools like Flash using the shape hints to tell Flash which vertices should end up where so it’s something that people coming to Synfig from tools like Flash will want to try and do.
You’re right that it’s better not to do things this way but a lot of people will want to try!
In addition, you often get commissions where you have to do things like morph between two logos that are already drawn and because the logos are already drawn the client will be mean and won’t pay for/allow time for one of the logos to be drawn again.
And, of course, some people will always be more comfortable drawing their keyframes in Inkscape rather than Synfig as they know Inkscape better and will assume there’s a workflow available where they can get Synfig to tween between their Inkscape keyframes.
Personally, for animation projects I’d always recommend using Synfig Studio as your drawing tool as well as your animation tool - I’ve found it’s always the best way.