Procedural collision filtering... is it possible in Unity?

When using physics layers are too limited and calling Physics.IgnoreCollision is not robust enough (because that causes the objects to ignore *all* collisions with eachother), is there any way at all to procedurally filter just a specific would-be collision from happening at all at the time it is about to otherwise occur?

 

There is no collision-without-response (yet?) but you can do sweep tests. Also triggers are a horrible hack you can look into (on/off)

 

Using triggers and coding all of your own collisions is the best I have come across so far. Its a pretty nasty hack, especially as we don't have all of the implementation details on how Unity actually handles collisions internally.

 

Sweep tests on OnUpdate are too expensive (asymptotic to O(n^2)) and coding collision response myself in a trigger handler would result in having to manually compute all of the details that are already otherwise conveniently stored in a Collision class with normal collision processing, and would certainly be a lot slower than Unity's collision response system. Worse, if I wanted my collisions to look consistent, I would have to fall back on using such a system for every collision even if I otherwise did not require a custom filter for a given object, because otherwise some collisions would be processed by Unity, and some by me, and the results would be unlikely to look the same.

I have just made a feature request for this, because it would be most useful.