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The key word you're missing there is attempt.
Before this change, if there were 2 projectiles and 5 targets, this could happen:
- P1 hits A, P2 hits B
- P1 and P2 both chain to C
- P1 hits C, P2 fizzles since it cannot hit target C.
- P1 chains to D
- P1 chains to E
P2 lost damage on D and E by targeting C. With the changes above, P2 will always target D. Then one will hit E and the other won't. Now:
- P1 hits A, P2 hits B
- P1 chains B, P2 chains D
- P1 hits C, P2 hits D
- P1 chains E, P2 randomly chains to A or C.
- P1 hits E, P2 fizzles since it can't hit A or C.
This is entirely correct.
The quoted section of the wiki has at some times been true of arc, but not of projectiles. A set of projectiles that are fired together can only hit each possible target once - the prevention of "shotgunning". Chain does not and never has removed that mechanic. The "Indended Behaviour" in the posted image is neither intended, nor has it been possible for projectiles since the removal of shotgunning. They would chain towards an enemy that's already been hit by one of those projectiles if there were no targets in chaining range that hadn't, but just like every other case of projectiles not being able to hit something if one of the same set of projectiles already had, they would be unable to hit that target, and would pass through with no collision being possible.
This was the case before 3.8.0 (and has been for a long time) and is still the case after 3.8.0. There were no changes to the anti-shotgunning code.
The only thing that changed was that when one projectile from the set chains towards a target, it notes that as an intended (but not hit) target, and other projectiles from the same set will prefer other targets to chain towards, if possible. This reduces the specific case /u/TL-PuLSe describes, where two projectiles would chain towards the same target, becaues both saw it as not being hit yet, but the second one to reach it would then be unable to collide with it. Now this will only happen in cases where there are no targets in chain range that don't have other projectiles already aiming at them.
The QA team did extensive testing on this change against various monster layouts, and showed it resulted in a substantial improvement in total damage output for most skills, with that improvement being greatest in cases where monsters were close enough to chain between without being super densely packed.
Monsters were tested at three levels of "packing": Medium, Dense
, and Superdense
, with several skills, and the number of hits recorded.
This table shows the results of initial testing. For each skill/packing combo, the left column shows the number of hits using the old behaviour, and the right column shows the number after the change, for several tests. At the bottom of each column is the mean number of hits over all those tests, and the combined cell below that shows the effective multiplier to the number of hits provided by the change.
As you can see, most skills tested with 3 chains dealt between 25% and 30% more hits as a result of this change against Mediumly packed enemies, with that dropping off but remaining a buff as they got more densely packed (with more targets in range, the chance of two projectiles chaining to the same thing goes down, and the chance that if they do, they'll hit something else after passing through goes up). Cobra Lash, with 6 chains, hits roughly 75% more times in the medium test.
There's a clear issue there in there with Ethereal Knives, which lost hits in these initial tests. That turned out to be because of the way those projectiles fade out - they lose their ability to hit things after a time, but they still exist to finish their fading animation completely for a time after that - if a projectile chained towards a target, then lost it's collidability, it was still "holding on" to that target and getting other projectiles to prefer not to hit it, where under the previous system, having multiple projectiles chain towards the same target was actually beneficial for EK, not because they could both hit, but because if one of them died before getting there, the other still could. As a result of that test, further changes were made to this system to account for the lifetimes of projectiles like EK, allowing them to "forget" their chained-at targets and free them up as soon as they couldn't hit them any more, and to improve the way the various layers of tests interacted and allow skills more broad scope to extend the base behaviour with their own extra tests.
I don't have a full second table, but after those changes were implemented, EK showed a similar improvement to the other skills, at roughly 30% more hits in the new chain system against medium packed targets.
Yes, the behaviour will be visually different, but this is because they are less commonly aiming at targets they won't end up being able to hit, and chain is actually a significantly better choice for projectile skills in general after the change.
tl;dr: this is a buff.
It was changed when shotgunning was removed.
The wiki is incorrect if it says a chaining projectile can hit a target more than once.
Arc can hit a target a second time, if if it wasn't one of the two targets the arc just came from, which means you need four targets for arc to continue back to the first target, but arc isn't a projectile so it works differently anyway.
As usual, /u/taggedjc is correct.