Support superquadrics in sdf actor

[Garyfallidis]

SDF stands for signed distance functions. Currently, our sdf actor manages sphere, torus, and ellipsoid.

We would like to add the support of the superquadrics. Check fury.actor.sdf for more info.

[haran2001]

Hi @Garyfallidis, I would like to work on this issue.

[haran2001]

Hi @Garyfallidis , I'm trying to add an sdf for superellipsoids (SE) under sdf_dec.frag
So far I've added an appropriate sdf for locating points, but only patches of the actor are being rendered on screen.
I suspect that some points inside the SE are producing a positive value by the sdf so it appears like the surrounding itself.

The sdf I'm using assumes the origin as center, but it's possible that fury applies a transformation to the co-ordinate system at some point and changes that, because of which the sdf produces wrong values, however I am not sure about this.

[haran2001]

I am expecting the following result

[haran2001]

But it's rendering this

[haran2001]

Any help or guidance regarding this issue will be much appreciated :)

P.S : This SE is the result of taking, epsilon1 = epsilon2 = 0.1 (square form of SE)