On Mon, 19 Aug 2019 17:41:16 -0400, William F Pokorny wrote:

>On 8/19/19 4:28 PM, Andreas Kaiser wrote:
>> 
>> see CSG::Compute_BBox() in CSG.cpp and Quadric::Compute_BBox(Vector3d&
>> ClipMin, Vector3d& ClipMax) in Quadric.cpp:
>> ...
>>              Make_BBox_from_min_max(BBox, NewMin, NewMax);
>>   
>>              /* Beware of bounding boxes too large. */
>> 
>>              if((BBox.size[X] > CRITICAL_LENGTH) ||
>>                 (BBox.size[Y] > CRITICAL_LENGTH) ||
>>                 (BBox.size[Z] > CRITICAL_LENGTH))
>>                  Make_BBox(BBox, -BOUND_HUGE/2, -BOUND_HUGE/2,
>> -BOUND_HUGE/2, BOUND_HUGE, BOUND_HUGE, BOUND_HUGE);
>> 
>> CRITICAL_LENGTH is defined as 1.0e06, BOUND_HUGE/2 as 1.0e10 in both
>> cases.
>> 
>> This code will never shrink/limit the resulting BBox like the comment
>> above might suggest.
>> It will 'blow up' instead all dimensions of a BBox if just one of its
>> dimensions exceeds CRITICAL_LENGTH (which is still smaller than the
>> resulting dimension(s)).
>>   
>> I have no idea what the original intention might have been.
>>
>
>That bit of code came in with v3.0, but I have no idea why. I 'think' it 
>might be doing what's intended...
>
>The aim isn't to shrink the bounding box, but rather to make it so 
>large, if already >1e6 on any side, that it is seen as an infinite 
>object and not included in normal bounding. BOUND_HUGE is larger than 
>MAX_DISTANCE (1e7). I say this without verifying that this the real 
>behavior though.
>
>Bill P.

I don't remember anything in the code where it might help to set a big
but finite AABB to +/- infinity.
Actually this turns off BBox testing for the corresponding object.

What should be done (and is done most often) is to clip all
coordinates of a BBox to +/-BOUND_HUGE/2.
IMHO this should be done in Make_BBox(...) always, not in the caller's
code.

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