On 4/10/23 10:49, kurtz le pirate wrote:
> The same macro but using the "disc" object show the issue
> (image on the right)

I believe what your are seeing is the fact the disc, like the plane, is 
defined in the code as having and inside (as being a 'basic object' 
rather than a 'patch object') so it can be used in CSG.

Neither the disc or plane have an actual finite inside. But, with the 
plane especially it's convenient to use it when defining many objects 
via csg - though the bounding of the result is often bad (infinite in 
some aspect or in total).

The disc being set up in a similar manner to the plane is questionable 
in my opinion. Perhaps when it got done 30 plus years ago it made more 
sense to do it. There have long been scenes where the disc 'is' getting 
used in csg & it's been left as is rather than treating it a pure, 
finite patch object.

Aside: The documentation says the disc's inside is no different than a 
plane's, but your image makes me wonder if it's not constrained to the 
radius of the disc in at least some aspects. Maybe due the 
inside/outside csg status flips somehow? There is not a completely, 
surface bounded inside region in your example, but it kinda looks like 
there is(a).

(a) - Maybe rays are constrained to the disc if they travel through the 
plane in which the disc sits though the insided-ness is still like the 
plane's when that inside test is run...

Don't know. I've never gone through the disc code in detail & never used 
it myself, IIRC, unless it was in code I picked up somewhere. Kinda want 
to play a little with it as I wonder, but, have not the time now.

Bill P.

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