Hi,

I understand now that my question was really not about libfive: thanks for pointing me in the right direction. I ended up reading a lot more than expected about what makes a distance function exact, what functions are usually exact, etc. For the record, this article was an eye opener to help me understand why a lot of functions are not exact.

One related question: is there a specific reason why the libfive cylinder_z function is not exact ?

There's no specific reason, other than a vague intuition that bounded functions can be faster than exact ones (although as IQ points out, exact functions may end up doing less work because they provide tighter approximations; I'm not sure if that's as true for interval arithmetic as it is for raycasting).

The historical reason is that the libfive standard shapes library was inherited through several generations of software (see this blog post), and the exact-vs-bounded distinction wasn't a consideration during early development.

Hi @omgitsraven,

I apologize for this very late followup but it took me a while to ponder this topic more seriously. I believe I understand what you explained and more generally, I understand that the "simple" boolean operations defined via min/max functions are not exact either.

The following example illustrates this: the resulting intersection object cannot be offset to obtain rounded corners for the intersection boundary between two simple objects:

from libfive.stdlib import shapes, transforms, csg, text
import libfive.shape
import studio

s = shapes.sphere(1)
b = shapes.box_exact_centered((1.8, 1.8, 1.8))
i = csg.intersection(b, s)
csg.offset(i, 0.1)


studio.set_quality(8)
studio.set_resolution(60)
studio.set_bounds([-10, -10, -10], [10, 10, 10])

So, my question is: how do those who use such frep systems manage rounded corners in general? Do they use different definitions of boolean operations?

Unfortunately it's not something I have much experience with; my impression is that it's used on exact shape definitions alone, before any boolean operations. One of the fun things about SDFs is that there's lots of different ways you can transform them, but unfortunately, many of those transformations, even the simplest ones, break some of the assumptions about what it's possible to do with a "pure" SDF.