On 30-10-2018 4:58, Robert Munyer wrote:
> The documentation explains the rendering problem that happens when one
> of the surfaces of the minuend in a difference operation is coincident
> with one of the surfaces of the subtrahend.
> 
> I've been encountering a similar-looking rendering problem even when
> there is no such coincidence.  In the scene attached below, I expected
> the center of the image to be a green solid surface, not a speckled
> "window" into the object's interior.
> 
> Question 1:  Is this a bug?

No. It is not imho.

> 
> Question 2:  If this is not a bug but a problem in the scene file...
> Suppose that Bar and Baz were written by different authors; which one of
> them is responsible?  Was the author of Bar supposed to avoid coincident
> surfaces, even though he was just unioning some untextured solid objects?
> Or conversely, was the author of Baz supposed to perform an audit of the
> structural details of the objects that he was differencing, just in case
> one of them might have its own subcomponents that have coincidences?
> 

Bar is the offensive element with a coincident surface at z=0. 
Obviously, Baz is unable to difference that coincident surface from Foo, 
leaving a /hole/ (/not/ a difference surface you may have noticed). My 
experience has always been to avoid coincident surfaces wherever 
possible, especially in complex situations. I leave the technical 
background to my betters. ;-)

-- 
Thomas

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