Translate object to the center despite rotation

Hi there,

sigh Not sure how am I gonna explain this…
You see, I am attempting to make a circle follow a ‘Stretch’ layer. In the attached example, you’ll see a black outline (resides in ‘PRO’ group) which is stretched according to ‘STRECH’ layer from 1u to 0u. The red ‘Circle’ layer (resides in ‘FAS’ group) should always translate to the center of ‘Stretch’ layer by axis X. Start the animation (0s- 2s) and you will understand what I mean.

The problem comes when you change angle (‘ROTATE’ layer), then the red circle will be off the ‘Stretch’ layer’s center. Is there a way to make the circle always end up in the ‘Stretch’ layer’s origin (X axis, Y should remain according to rotation) despite the change of angle?

Any help is greatly appreciated because I ran out of ideas. I tried using sine and radial composite conversions but seems I just do not understand some trigonometric (is that the right word?) basics…
StretchEx.sifz (1.72 KB)

What if you Group FAS and PRO into a new group an use the group transfromation widget of that new group to rotate instead of the rotation layer?

No-no, that’s the point why I made rotation scheme in such, well, more complicated way. Using your technique results in the red circle moving by the Y axis too and I need to avoid that.

I’ve attached a corrected example.
Look at the animation starting from 2s to 4s, I think now it clearly shows what I want to achieve. It was manually animated and I want it to be calculated automatically, depending on the current rotation.
StretchEx1.sifz (2.13 KB)

Spent a few hours on this problem but I can’t put my finger on it. Either the circle goes of center or the line does not what it is suppose to do or the circle stays on center but rotates alone the wrong axis together with the line. Guess it is far beyond my pay grade, of course I am not a mathematician nor a programmer. Where is Genete when you need him :smiley: ?

Thanks for trying! You spent hours to help some guy on the Internet. Well, that guy really appreciate that :wink:

Yeah, exactly what I was thinking too :slight_smile:
From the very beginning, I was hoping he will fly in wearing his blue costume with the letter ‘G’ on it and the day would be saved! Well, guess we’re on our own now…

You are welcome. When people post a sif file with a problem I usually have a look. In the first place because I am intrigued and second because I always reason that it could be a problem that I could come across too, so a solution is helpful to both parties and any problem solved helps me to dig deeper into the depths of Synfig. Besides that, I am a big fan of your fury creatures :smiley: