De yellow line is going to rotate around its origin, like the radius of a circle. The idea is that red line is attached to the end of the yellow line (like in the picture), but remains horizontal as it follows the yellow line through its rotation.
How do I do this? I already tried linking the origin of the red line layer to the vertex point of the yellow line, but Synfig says they cannot be linked (because of different types).
Excuse Bazza, he isn’t very good with English (so am I), but I guess he meant that you should put every line in a separate group and then counter-rotate the second one.
Please examine the attached example.
It simply counter-rotates the second line, so if you set ‘ROTATE’ layer to 90, the ‘COUNTER-ROTATION’ will become -90 and that will correct the difference. Check ‘Origin’ parameters of rotate layers, it’s important. This technique uses export functionality of Synfig, you can read about here: https://wiki.synfig.org/Export