From Synfig Studio :: Documentation
About Twirl Layers
"Twirl" is the layer which deforms lower layers so that it seem as the vortex. The intensity of the vortex is set over the rotation angle - higher, the more intense.
Size of vortex is determinated by the radius of a circle, and distortion can be activate separately for both the sides – inner and outer.
Parameters of Twirl Layers
The parameters of the twirl layers are: