"Fractracer" <lg.### [at] gmailcom> wrote:

> Who better than an eagle could help me for the feathers ;)
Ha!  It often gets amusing around here.
I still remember your help with circumscribing spheres around triangles  :)
I might want to try a variation of that using geometric inversion...

> Thank you for your help, I have a quick look at the code, complicated, but whith
> tima and patience I think I can adapt or modified the code, maybe using
> sphere_sweep for a curved rachis...

I've had a chance to edit it for clarity, and I added 2 (crude) blocks of code
to restrict the asin argument to between -1 and 1.  As I'm sure you've noticed
it throws a "domain error in asin" error - probably due to small rounding
errors.
Maybe soon I'll decipher the meaning and function of the calculations - it seems
at first glance to be some repetitive sphere-cylinder sweeps that move up and
then down the rachis.
I think the rachis could be redefined with a spline or array, and then the rest
of code could be adjusted to make the rest of the feather using those variable
points rather than a fixed x-coordinate.

It looks like _sym probably needs to be limited to between 0 and 1 (I haven't
extensively tested this yet)
but _fun is a variable that is used to calculate a probability which seems to
control the appearance of imperfections - the peeling and separation.  I've only
varied that from 0.5 to 1.3 in my last test, and it was fine.

> Also I will add the possibility of changing the textures (easy).

Yes, I was wondering how to get something other than a banded pattern, and more
of a realistic pattern.  Possibly as another parameter for the macro so that the
pattern can be defined in the scene and passed to the macro.

There also seems to be some unnecessary calculations, and "magic numbers" - it
would be great to simplify a lot of that, move the equations out into some
descriptive #declare or #local statements, and then use those meaningful
variable names in the calculations so that it's easier to follow what's going
on.

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