> I think the last lil screenshot in that posted forum link IS what he
> is talking about. It's a hole, trimmed in a subdiv surface, nurbs-style.
> Both the subd surface, and the hole boundary are editable.

I see now - I think that got edited in later. That is interesting that Maya has that feature, I don't think that there is any other sub-d modeler that can handle it like this. But most of the time trimming or booleans in a sub-d modeler does mean dicing polygons into smaller polygon slivers.

I wouldn't be surprised if Maya was actually converting the Sub-d surface internally into a NURBS equivalent for that trimming operation. It is one of the few things out there that has a function to do this kind of a conversion. Note that this is the opposite direction conversion (Sub-d to NURBS) from the one mentioned at the start of the thread (NURBS to Sub-d).


> There are many papers on applying nurbs style trimming to subd surfaces,
> and I'd kill to see such a modeler built ( Other than one real expensive
> high-end cad package ).

It is cool that there is different research happening on trimming subd surfaces, but there is one big problem with implementing any of these, which is data exchange.

There is no common file format that currently exists that can contain subd surfaces with trimming information. If you were to create a modeler using something completely new like this, you would only be able to use your full fidelity geometry within that one environment. That's a pretty significant problem.

On the other hand, there are several common file formats that can hold trimmed NURBS surfaces.

So because of this what I think you will see happening in the longer term, is that NURBS modelers will offer Sub-d type tools as an alternative way of constructing a NURBS surface patchwork. Like instead of doing a sweep to create a surface, you could have a polygon cage that created a set of surfaces from it. But the resulting surfaces will be all NURBS surfaces joined together. Because the result is all NURBS surfaces, they could be trimmed and booleaned, etc.. just like any other NURBS surface. This will then preserve the trimmed surface information for data exchange.

So I wouldn't be too surprised if you see Sub-d trimming appear really mostly inside of NURBS modelers eventually and not really inside of current Sub-d modeling environments.

- Michael