False positives in culling test: btDbvt::collideKDOP

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youle
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Joined: Sun Mar 26, 2017 12:17 pm

False positives in culling test: btDbvt::collideKDOP

Post by youle »

Hello, I work on upbge (a fork of Blender game engine).

I noticed that bullet culling test returned false positives as described here: http://www.iquilezles.org/www/articles/ ... orrect.htm
This concerns big objects. I did a test file and a bug report here: https://github.com/UPBGE/blender/issues/443 (it needs to build upbge sources with the patch I shared applied to see the issue).

(This issue is in another function in game engine source code: KX_Camera::BoxInsideFrustum too)

I didn't check at new bullet sources if this has been fixed. We use the same version of bullet than Blender (2.83 iirc).

I wanted to have the opinion of Erwin Coumans about this issue. Is it intended to have a limited amount of false positives to alleviate the culling test or is it an issue?

Thanks for your answer!

EDIT: I can provide a build if you tell me your OS
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Erwin Coumans
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Re: False positives in culling test: btDbvt::collideKDOP

Post by Erwin Coumans »

It is best to create a small reproduction case that doesn't require any external source code, but only the Bullet souce tree from http://github.com/bulletphysics/bullet3. Then file it to the Bullet issue tracker.

You likely want to use double precision (BT_USE_DOUBLE_PRECISION) and see if that helps.
youle
Posts: 2
Joined: Sun Mar 26, 2017 12:17 pm

Re: False positives in culling test: btDbvt::collideKDOP

Post by youle »

I understand. Thanks very much for your answer. Unfortunately, this would be very complex to me to learn how to use bullet API, see how we create a GUI, draw camera frustum and AABB with different colors, set up the intersection check...

I think we'll fix the problem in bge sources (in gameengine folder without modifying bullet sources) using the solution I mentionned which works for parallelepiped rectangle intersection with camera frustum (for frustum vs frustum intersection we use this: http://www.yosoygames.com.ar/wp/2016/12 ... s-frustum/)

If some day we have the time, we'll try to make a bullet file to see and report in the issue tracker if there is a problem.

Thanks very much for all your works in Blender and bullet!

EDIT: Maybe we have an issue with our AABB, sorry. I'll edit if I have more infos
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