>  Their problem is that automatically creating rounded corners for any
> given object:
>
> 1) is impossible in the general case,
> 2) in many cases where it's possible it results in extremely slow renders,

Those first two are not really problems though - ie we shouldn't say not to 
include a feature because it won't work with all possible objects and might 
result in extremely slow renders sometimes.

> 3) would require tesselating the object and rendering the resulting mesh
>   (with the corner modifications).

That's not the only way to do it.

>  POV-Ray, however, handles mathematical primitives (such as boxes and
> planes) and their CSG. Rounding their corners is a problem which is
> several orders of magnitude harder.

But not impossible, look at any CAD software that manages it with 
mathematically defined CSG.  The problem I see with POV, is how to specify 
which edges you want to be rounded, so far we have no way of specifying 
edges in the SDL.

I have no idea how CSG objects are stored internally in CAD software, but at 
each stage of the CSG you can somehow specify edges and faces etc to apply 
rounds and chamfers to.  I don't know how you would attempt to replicate 
this in a text-based way.

Internally, the POV engine would need to see what faces were connected to 
the specified edge, and remove/generate the correct geometry to round that 
edge.

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