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Frustum Box Intersection (again i know)


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#1 derKai   Members   -  Reputation: 227

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Posted 04 November 2013 - 09:42 AM

hi,

im currently working on frustum culling and looked for frustum-box intersection tests.

i found a tutorial appearing all the time: http://www.lighthouse3d.com/tutorials/view-frustum-culling/geometric-approach-testing-boxes-ii/

even here in the forum: http://www.gamedev.net/topic/512123-fast--and-correct-frustum---aabb-intersection/

 

during debugging some objects that should be culled were rendered so i looked deeper into it..

i made a picture to visiualize my problem..

 

FrustumBoxTest.png

 

is it possible that the algorithm misses that case?

what is the common solution to address this? I'm fine with AABBs ;)

 

thanks

- Kai



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#2 raigan   Members   -  Reputation: 619

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Posted 04 November 2013 - 11:57 AM

Here's a pretty great -- and succinct -- article on doing this right: http://www.iquilezles.org/www/articles/frustumcorrect/frustumcorrect.htm



#3 eppo   Crossbones+   -  Reputation: 2298

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Posted 04 November 2013 - 12:14 PM

Yes, this special case will not be culled. A box needs to be outside one of the clipping planes/lines in its entirety to be able to be culled.

The reason this is not such a big deal is the further away the box from the camera is the larger it needs to be to satisfy the above "unclipable" conditions. 

Likely, in practice only a few objects will fail this way, so it's often not worth it to write a more expensive test.

 

If you do want 100% correct results, the test would essentially become a convex overlap test. A separating-axis test can solve this. 


Edited by eppo, 04 November 2013 - 12:43 PM.


#4 derKai   Members   -  Reputation: 227

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Posted 06 November 2013 - 03:29 AM

Thanks for the confirmation, eppo ;)

to not increase the computation costs i decided to fit a bounding sphere around the frustum and test agist this first.

 

@raigan these are a lot of tests per box.. maybe there is a more optimized version of that method (i'll look into it if there is time and keep you posted)


Edited by derKai, 06 November 2013 - 03:29 AM.





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