[0.18.26] Pathing edge case with artillary and biters
Posted: Fri May 22, 2020 7:33 pm
I've found an exploitable edge case relating to biter pathing and the use of artillery. I was somewhat conflicted about posting this, as I have a save that (ab)uses this extensively as a defense mode 
Summary
If you put an artillery cannon on an island, biters will aggro it, but be unable to path to it, so they stay stationary for ~10 seconds, and then run away to another nest. As a result, the artillery can fire with impunity and be completely safe from retaliation, even though the enemies could really get close enough to damage it and anything around it (especially the spitters).
The huge range of artillery means that it becomes a quick and easy way of defending enormous swaths of land, since any spawning groups that "set up" in the range of a cannon will be immediately destroyed. A border of overlapping turrets can require surprisingly few cannons and a very simple rail network to keep them supplied with the occasional ammo.
Even clearing out huge nests with artillery becomes trivial, as the massive waves of biters never arrive at the cannon, so no extra defense is needed.
Expected behavior
I'd expect that biters would run as close as possible to the turret when they aggro. If they still can't reach it, they could destroy anything within range before leaving.
Steps to reproduce
https://youtu.be/e7tQWp20PpY
Summary
If you put an artillery cannon on an island, biters will aggro it, but be unable to path to it, so they stay stationary for ~10 seconds, and then run away to another nest. As a result, the artillery can fire with impunity and be completely safe from retaliation, even though the enemies could really get close enough to damage it and anything around it (especially the spitters).
The huge range of artillery means that it becomes a quick and easy way of defending enormous swaths of land, since any spawning groups that "set up" in the range of a cannon will be immediately destroyed. A border of overlapping turrets can require surprisingly few cannons and a very simple rail network to keep them supplied with the occasional ammo.
Even clearing out huge nests with artillery becomes trivial, as the massive waves of biters never arrive at the cannon, so no extra defense is needed.
Expected behavior
I'd expect that biters would run as close as possible to the turret when they aggro. If they still can't reach it, they could destroy anything within range before leaving.
Steps to reproduce
- Find (or make) an island at least two squares of water away from land (one square used to work, but I'm not sure if it still does)
- Place a cannon on the island
- Optionally wire up some inserters/underground belts/trains to keep the turret packed with ammo
https://youtu.be/e7tQWp20PpY
