Request to developers about OpenSubdiv

Huge request to tune some coefficients in which the smoothed cube becomes an ideal sphere, and smoothed square becomes an ideal circle. It seems insignificant, but it is not.

For example, if you want to create a round hole, enough to remove one polygon.

[ATTACH=CONFIG]390418[/ATTACH]

Presently time the smoothing square becomes “almost” round. But angles of the hole is particularly noticeable when the axis is rotated in this.

[ATTACH=CONFIG]390417[/ATTACH] . [ATTACH=CONFIG]390416[/ATTACH]

To fix this we need to use a concave polygon, which often creates problems.



Or create loops through the whole model.




This greatly increases the number of polygons, and can cause problems in other parts of the model. For high poly models it creates a lot of difficulties, especially when a few holes.

This is just one example. Often, in order to achieve a beautiful smooth the need to make great efforts.

I have long been using Blender and have dreamed about this fix. Now, when OpenSubdiv not yet entered into Release, can make it. Alternatively, we can make a separate mode for this.

In https://developer.blender.org/rB3524676036c370822344f1c80b191d34644b3745 have been prompted to do so for the default SubDiv, but it was rejected because of backward compatibility.

EDIT: It is always possible to make a circle with angles using crease edges, converse is not possible

It’s not just a matter of tweaking some coefficients (There are no coefficients to tweak in fact. It works by putting points at vertex, face and edge barycenters and connecting them, then repeating it over and over). Catmull-Clark is a recursive subdivision algorithm that gives a particular limit surface, and that surface is not perfectly round for a 4-sided cylinder. It’s designed that way. Or perhaps you may consider it an imperfection. It doesn’t matter.

More importantly, the whole point of OpenSubdiv is that it works the exact same way and gives the exact same limit surface in all the 3d packages that use it. Changing it just for blender (if it were feasible, which it isn’t) would be a disservice, leaving it with yet another non-standard component.

  • it’s a non sense to make a cylindre from a cube. I see this often and I don’t understand why people do that.
    You want make a cylinder, the create a cylinder, we are not in 1995, we can use more polygons.

This is just an example. If the cylinder is part of the model, which wills subdivided, you can not do it from a large number of polygons.

The patch https://developer.blender.org/rB3524676036c370822344f1c80b191d34644b3745 is an example of what is possible. For compatibility, we can make it a separate modifier option.