"quickfur" <qui### [at] quickfurathcx> wrote:
> Hi all, I'm making a simple model of a creature for my scene using CSG, and
> I'm having some trouble modelling the creature's eyelids. Basically, I'm
> using a sphere_sweep object to model the eyelids, and I want the eyelids to
> lie on the surface of a sphere. I have 5 spheres in the sweep, 3 of which
> lie on the sphere and the first and last are adjusted by a macro that
> models (or tries to) different eye expressions, interpolated by
> cubic_spline. How do I mathematically ensure that these two "control
> points" are placed so that the resulting sphere_sweep object always lies on
> the surface of a sphere? (Well, actually, half sunken into the sphere since
> all I'm doing is modelling the bulge along the edge of the eyelids.)

I would suggest looking up the trace command (yes it can be a bit tricky at
first but look at the povray posts about trace if you get completely
bewildered).  You would need to use this once for every element in your
sphere sweep unless the area where your eyebrows meet the face is
relatively flat - in that case you could use it once for the entire sphere
sweep object after you have created it.  Doing it this way, I imagine that
you could get your curve correct in the y-direction (looking directly at
the face) and then use the trace function on the individual array elements
to set the z-location (where eyebrow touches face) of each point.
I have never tried this so I'm not sure if moving the points in the
z-direction will throw the whole curve out..but it's worth a try.
If this idea is feasible, hopefully someone can expand on it or explain it a
bit clearer.

> I can
> hand-adjust specific cases of the eyelids to make this happen, but I'm
> making a little animation and want this to be automatically handled by a
> macro.
>
> Also, there is the harder question of how to create the right shape (given
> the parameters that specify the sphere sweep) to subtract from the sphere
> to make the eye socket so that the eyeball inside is visible. Any help
> would be appreciated. Thanks!

As far as the eye sockets are concerned - I'm not why you need a
sphere-sweep here but I may have misunderstood the problem.  Can you not
simply CSG-Difference two sphere shapes out of the main sphere?

All the best for your animation!

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