Basher Walks into Terrain

[Simon]

A basher oddity found by Icho during multiplayer in Lix 0.10.5. Thanks! Here's a reduced example level.

Rule 1: Bashers walk forward during some frames in their cycle. This forward movement is allowed to enter terrain, i.e., the basher's foot is allowed to move into and through terrain.

Reasoning behind rule 1: Either the basher's swing removed all terrain here, therefore we won't walk into earth anyway. Or the basher hit steel, immediately stopped bashing, and won't walk forward.

Rule 2: During the walk forward, bashers lower themselves into holes. Bashers never gain height.

Reasoning behind rule 2: We removed all terrain onto which we might step upwards, or cancelled on steel in the way. Either way, there is no need for the basher to ever rise. But the basher may try to walk over holes, and the basher should certainly fall into such holes if they're deep enough. If the holes are shallow, it's okay for the basher to continue; shallow holes shouldn't break mental pathfinding.

As a result of rules 1 and 2 combined, the attached level Basher Walks into Terrain is solvable (saves 1 of 2, using 1 cuber, 1 basher, and a few jumpers to position the cuber and basher). The thin white line is steel.



The most noticeable effect here is that we can clip through a particular arrangement of steel.

The second effect is that a basher falls through an arrangement through which a following crowd would not fall. The non-falling crowd alerted Icho in the first place.

I don't have a good solution.

• Basher source on github
  
• github #47: Basher/Miner Interact with Blocker, Passes Through Wall, a closely related bug that comes from the same two rules.
  
• geoo's post from 2015: basher/miner❤blocker interaction, desired behavior? -- the same bug as #47, but on Lemmings Forums instead of on github.
  

-- Simon