[From the 3.4.1 release notes]
Trigger notification events for trigger-trigger pairs have been deprecated and will be omitted by default. See the 3.4 migration guide for more information.
[From the 3.4 migration guide]
Trigger shapes will no longer send notification events for interactions with other trigger shapes. For PhysX 3.4 there is the option to re-enable the reports by raising PxSceneFlag::eDEPRECATED_TRIGGER_TRIGGER_REPORTS but this option will no longer be available in PhysX 3.5. It is recommended to not make use of eDEPRECATED_TRIGGER_TRIGGER_REPORTS and instead use a trigger and a non-trigger shape, both with the same geometry and local pose, to emulate getting notifications for overlaps between trigger shapes.
I have an entire projectile system built on this idea, where energy projectiles (particle systems, non-physical in the graphical sense) are fired in the game, and various shots can contact/touch and pass through each other without affecting the physical path of the shot. But notifications of their contact with each other is essential to changing shot game play attributes.
I feel there is a real need for collision detection without a collision response/reaction, and losing this feature ends that. I fail to see how creating two overlapping shapes of the same size, orientation, (where one is solid and one is a trigger, call them “solid-triggers”) replaces this situation. Exactly how would “solid-triggers” ever be able to penetrate each other the way classic trigger-triggers did?
If anything it makes everything more complicated as now there is a redundant non-trigger shape in the mix, that does not have the ability to pass through other objects (solid-triggers) in a ghost like way.
From a performance point of view, I can see it being, one less thing, contact scenario to worry about, but in my opinion leaves a giant hole where a once useful feature existed.
Is it possible for this feature to remain? I can think of many situations where it is/could be used.