Multiple transformations

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Posts: 1
Joined: Mon Jan 14, 2019 10:30 am

Multiple transformations

Post by DSx » Mon Jan 14, 2019 11:02 am


I have been experimenting with the collisions side of Bullet Physics. It worked fine initially. However I am trying to figure a strange behaviour I found recently.

I am working with RigidBody collisions without the physics simulations. The issue I am having happens after applying multiple transformations in some cases e.g. scaling after translation - if that happens then no collision gets detected. However, it works fine when applying a single transformation or when the first transformation is the same for both objects.

General layout of the process: create world and rig bodies, apply transformations to center of mass and updating aabb, perform contact tests.

Strangely if I set the initial shape size to the scaling I want and only apply translation the detection works. Even though the final vertices are the same as in the two-step transformation. I am getting the vertices by multiplying by the object world transform.

Any idea what might be the issue here - or what I am missing?

Thanks for your help.

Posts: 7
Joined: Sun Mar 11, 2018 9:34 am

Re: Multiple transformations

Post by niad » Tue Jan 15, 2019 9:17 am

If you are just using it for collision detection (everything is inactive) perhaps the broadphase doesn't see a need to update the AABB's after they are initially inserted.

Try calling btCollisionWorld::updateAabbs() after you have moved your bodys.

You probably need m_forceUpdateAllAabbs on if you aren't running simulation.

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