I'm using packed ice to help push mobs around. I've noticed that no mobs will spawn wherever I have the packed ice. To verify, I tested by expanding the sections to be giant rectangles of packed ice. Mobs spawn up to the edge of the ice but never on it. Legit?
I can confirm that this is not a Mojang thing; mobs can spawn on packed ice but cannot on regular ice. But it appears that there's more going on because I do recall seeing mobs spawn on areas of packed ice in cold (overworld) biomes. Just to rule out the obvious: you're sure that the conditions for mob spawning are met there?
Yep This area is a hunting ground and spawned plenty of mobs before I mucked with the floor. I've tested by running back into and out of mob range for about 30-minutes today. It's possible I was just unlucky but since mobs were spawning right along the edges of the ice on a one-block wide border the effect was a little comical. I can expand it further just to be really sure, but I hate to waste time if it's a bug.
You can change a part / patch within the packed ice surface to a different material and check if something will spawn. Try Netherrack and perhaps stone bricks at the same time.
I gave it another 15-minute try just now...when I logged in 3 pigman spawned on the ice, after that I saw one chicken and I think one other pigman spawned on it. (Can't be sure if that last just wandered on.) Blazes and wither skeletons spawned only on the nether brick next to the ice, and on the nether rack nearby. So maybe I've just been really unlucky? I'll put a little more time into it later on and see if I can isolate something.
put it into nether brick stuff doesn't spawn otherwise i learned this when made spawning platforms out of cobble
Gave it another 90-minutes. Nothing but a couple of pigmen have spawned on it. I believe M4ster_m1ner and crazy_X_gamer are right. The bug isn't that the floor is ice...it's that the floor is NOT nether brick. What this tells me is that the zoning for the fortress area sections is wrong. Fortress mobs can spawn: In fortress tile sections, made of any material. In a fortress area outside of tile sections, if they're made of nether brick. (e.g. Hand placed nether brick.) I believe that invalid tile section data would explain what I'm seeing: Blazes and wither skeletons spawning in the nether rack. (There is an invisible fortress tile there.) No blazes or wither skeletons spawning on the ice. (Doesn't count as fortress tile.) Blazes and wither skeletons spawn on nether brick. (But..because it's inside a fortress area, not a fortress tile.)
Bumping this because of the serious time impact to anyone building a nether fortress farm. Also going to request a title change I guess.
Are you building in an area that was likely generated pre 1.8? If so, those locations are known to of been "shifted" and no longer line up structure wise. Pre 1.8 (or was it 1.7 maybe) we had to turn off the 1.6 "Structure Saving" code due to serious performance problems with it, but those issues were resolved in one of the recent major updates. So anything uncovered before it got turned back on, relies on world generator config, which will not line up correctly. Only on more recent discovered fortresses, post the fix, will consistently behave.
Thanks for the response. Yeah. This includes everything visible in the LiveMap circle, right? (pre-quartz era) Would the tiles be completely different or just shifted? I have a nice location with multiple cross intersections and a double blaze spawn that I'd like to keep. I would even spend the time to write a mapper if the manner of the shifting was deterministic and didn't require the world seed. I have to think the mappings are pretty close because otherwise I'd see no fortress mobs.
Thanks for the leads. After some further research based on that, I found what I think is happening -- in 1.6.1 (13w18a) a bug caused the regeneration of tiles within the fortress bounding boxes. https://bugs.mojang.com/browse/MC-15547 I did some testing and it seems that yes, the bounding box is respected but some tiles were regenerated (or deleted) within the larger bounding box of the fortress. Mojang's addition of the spawn-on-nearby-nether-brick rule masks the effect. Ugh! Edit: The smoking gun? "When they added chests to nether fortresses, they used the same random object to stuff the chests as they used to generate the fortress. The result being that initially the fortress will generate the same as before... until it creates a chest, at which point the RNG will get thrown off, creating an entirely different fortress from that point on."
