idupree/Lasercake — comment on commit 862c1d44fe50653186f7a5a849c9fcfcc7898b5e
File:  line 0
By elidupree:

In fact, this change might be good for the opposite reason...!

The relation needs to be symmetric, or everything blows up. But what about reflexivity and transitivity? Right now the code relies on them, but does the physics rely on them?

Reflexivity: If something was non-self-related then a whole mass of it would always show up in the collision detection - every tile would be independent. I don't see a reason we'd want that, but I also don't see a reason-based-on-principles that that's an impossible thing.

Transitivity: Without transitivity, you'd have situations where there are three masses of stuff - imagine them as three equal slices of a pie graph - where two of the borders between them don't have collidable interfaces, but the third does. Weird situation? Yeah, but I don't see anything wrong with it - and it could make sense if, for instance, those two materials have special properties at the interface between them, while the third is inert with both.