[MC-120010] Zombified piglin and wither skeleton avoid walking through fire or over magma blocks

The bug

Zombified piglins and wither skeleton avoid walking through fire or over magma blocks if there is an alternative (not much longer) path, even though these blocks aren't hazardous to them.

Note: In previous versions these mobs would never walk over these blocks, even if there was no alternative.

Exceptions

It appears under certain circumstances they do walk over these blocks, so make sure to avoid them when trying to reproduce the bug.

In general mobs apparently walk through fire and over magma blocks if this is the only available path.
Wither skeletons walk over magma blocks if there is only one, however when two are placed next to each other, they won't walk over them.
If the alternative path is much longer (or they are already in fire or on magma blocks?) they walk through fire / over magma blocks.

How to reproduce

Code analysis

See this comment

Linked issues

is duplicated by 2

MC-103366 Zombie pigman and wither skeletons don't walk in magma blocks Resolved

MC-259988 Zombified Piglins avoid fire even though they are immune to it Resolved

relates to 2

MC-13497 Wither skeletons and zombie pigmen won't go through lava to get to enemies, even though they can't burn Resolved

MC-102278 Non-fire resistant hostile or neutral mobs pathfinding do not avoid the magma blocks Resolved

Attachments

Wither skeleton avoiding magma blocks (1.16.2).mp4

Zombified piglin avoiding magma blocks (1.16.2).mp4

Comments 24

Fritz Meyer 2017-08-07T03:07:18Z

Just noticed that they are also avoiding magma blocks.

bemoty 2017-08-13T18:02:08Z

Can confirm. They indeed try to avoid fire, sometimes a Pigman decides to go through though.

Fritz Meyer 2017-08-13T22:55:14Z

@Bemoty
I think sometimes they get pushed in by other pigmen and once they are in they walk the rest of the way. But I've never seen one enter fire on it's own.

pokechu22 2017-08-13T23:01:47Z

Take a look at the image from 16w14a and 16w15a, which shows the pathfinding debug renderer (not usable in normal gameplay, but documented here). You can see that the path has DANGER_FIRE and DAMAGE_FIRE indications on the fire, even though it's pigmen that are pathfinding. So, yes, the pathfinder definitely sees that there's fire and tries to avoid it, even though there's no real reason.

I checked the code, and it seems like blazes set the priority for both of those to 0 (normally it's 8 as you can just barely make out in the picture), meaning that their pathfinder is willing to enter them. The same thing could probably be done for pigmen and they would then happily run through fire.

bemoty 2017-08-14T00:49:51Z

@unknown I already checked the code for pathfinding and even got them to walk through fire by returning PathNodeType.WALKABLE for EVERY mob when they see fire in the method net.minecraft.pathfinding.WalkNodeProcessor.getPathNodeTypeRaw(). I didn't realize that mobs could have different danger/pathfindig-priorities. Not 100% familiar with Minecraft's code, yet. 😛

Thanks! Also, that debug path plugin channel is super cool! Didn't know something like that existed.

Yep! This bug can be fixed by setting the path priority for both DAMAGE_FIRE and DANGER_FIRE and maybe LAVA to 0.0F. Setting the path priority can be done by using the method setPathPriority. After that, Zombie Pigmen will also run through fire to kill you if you are mean to them.

net.minecraft.entity.monster.EntityPigZombie

public EntityPigZombie(World worldIn)
{
	super(worldIn);
	this.setPathPriority(PathNodeType.DANGER_FIRE, 0.0F);
	this.setPathPriority(PathNodeType.DAMAGE_FIRE, 0.0F);
	this.isImmuneToFire = true;
}

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