how to do a twirl effect on a curve?

[RogerSWD]

Referring the light grey background of the attached. Thank you.

[GarryP]

What are you starting with before you make it ‘twirl’? An example image/document would help us to see what you have.

And do you need the result to be vector, or bitmap, or does it not matter?

[RogerSWD]

Let's consider a circle. Does not matter if it is vector or raster. I can switch to Affinity Photo, if required.

Thank you.

[joe_l]

10 minutes ago, RogerSWD said:

I can switch to Affinity Photo, if required.

Affinity Photo has a Live Filter / Filter for a twirl.

Looking at your example, I would use a star shape instead of a circle.

[RogerSWD]

twirl does not work on solid colours.

[walt.farrell]

23 minutes ago, RogerSWD said:

twirl does not work on solid colours.

Here's a Twirl Filter applied to a solid red star shape:

That may not be what you want, of course, but it does "work" with solid colors.

[Old Bruce]

To my eye that appears to be a semicircle with a brush applied to the stroke. You may need to make a brush but try with Inks or Oils. Here I doubled the stroke and reversed the direction of one of them.

[RogerSWD]

I was thinking a brush might be the way to go. Thank you.