[BubRoss]

> modeling pure polygon models, e.g., for games, is a different activity

It really isn't. I think you want to drive home some distinction, but the vast majority of work flows model straight polygons and the only difference is that they know they are going to be subdivided and smoothed later by the renderer.

You say that there are all sorts of different issues with subdiv surfaces, but it just isn't true. Modelers and texture artists might look at everything smoothed to make sure there aren't any surprises in the interpolation and distortion in the UVs, but everyone deals with the raw polygons.

[dahart]

Yes, exactly, knowing they’ll be smoothed is a big difference, it leads to different choices. Looking at a smoothed surface during the modeling process is an even bigger difference than looking a mesh all the way through. Knowing how they’ll be smoothed is important. What about creases? What if you want a creased edge smoothed and it’s part of two separate mesh groups?

You can subdivide polygons without smoothing them, and people still do polygonal modeling without planning for subdivision, and produce models that aren’t intended for smoothing and wouldn’t smooth nicely, so it is important to be clear in your language that you’re talking about a subdivision surface and not just polygons. Why the resistance to just saying subdivision surface, since that’s really what you’re talking about? I agree with a lot of your points if I replace “polygons” with “subdivision surface”.

My issue with what you said far above is the claim that smoothed surface representations require extra tooling, and you claimed that “polygons” don’t have these issues. The problem with that is that a subdivision surface is a curved surface representation, and it does come with extra tooling. Just because it’s easier than NURBS, and just because you get to use a lot of polygon tools, that does not mean a subdiv workflow is the same thing as a polygon workflow. Hey it’s great if the tools are getting so good that people confuse polygons with subdivs. Nonetheless, a pure polygon workflow can mean things that aren’t compatible with smoothing or subdivs.

[BubRoss]

> What about creases?

Creases are done by just making polygons/bevels/line loops close to the edge that needs to be sharpened.

> What if you want a creased edge smoothed and it’s part of two separate mesh groups?

Mesh groups don't have to mean their polygons don't share vertices and this is one of the reasons why - you need to be able to interpolate the attributes of the vertices, like normals.

> You can subdivide polygons without smoothing them, and people still do polygonal modeling without planning for subdivision, and produce models that aren’t intended for smoothing and wouldn’t smooth nicely, so it is important to be clear in your language that you’re talking about a subdivision surface and not just polygons.

I'm not concerned with what random people do. Professionals just say polygons in general and the workflow is all about working with the polygonal mesh directly. If two people are both making polygonal models and they will save them as .obj files, but one will be smoothed at render time , they don't say they are working with a different type of geometry. Technically there are actually many different ways to smooth polygons.

> My issue with what you said far above is the claim that smoothed surface representations require extra tooling,

No, I explained that nurbs require extra/different tools. Technically if someone (like pixar) were to use extra attributes like edge crease amounts on subdiv surfaces, some tools would need to address that, but that's not on the same level as the difficulty of working with nurbs.

> Nonetheless, a pure polygon workflow can mean things that aren’t compatible with smoothing or subdivs.

I think when you say things like this you are trying to salvage your confusion, but it really doesn't shake down like this. Any mesh can be smoothed and unless you have messed up meshes it works well and no one has an eye.

To recap: nurbs are a nightmare to work with, everyone works with regular polygons that could be saved as an .obj, they get smoothed at render time. Everyone calls them polygons because that is what they are working with and it has been this way literally for decades. Try not worry too much about it.

[dahart]

> No, I explained that nurbs require extra/different tools.

I’m sorry if you feel defensive. I was responding to your explicit inclusion of “other curved surface representations” besides NURBS here https://news.ycombinator.com/item?id=23043791 and here https://news.ycombinator.com/item?id=23044537

Really just pointing out that a subdivision surface is literally another curved surface representation, does have some conceptual differences from polygons, and can be ray traced without subdivision. Calling it polygons was confusing to me, but now that I understand what you mean, call it polygons if you want.