The bug
Since 1.14, slimes in spawn chunks (and from spawners?) spawn less frequently if there are any blocks (even glass) above their spawning spaces.
To reproduce
Find a slime chunk
Clear it completely, down to level 4 (for example) and make sure the spawning platform is adequately lit
Count how many slimes spawn in a certain time frame
Fill layers 20 to 64 with blocks (for example, you can also choose another amount of layers)
Count again how many slimes spawn in the same amount of times
→ ❌ Significantly less slimes spawned
Original description
In my survival, I built a slime farm and I checked for slime chunks, and yet, slimes still aren't spawning. So I went to creative because I have cheats on and tried to spawn one with an egg but these slimes will just pop into existence and then pop out. I tried this in my farm and on the surface for about 10 minutes to no avail.
Linked issues
is duplicated by 9
Attachments
Comments 16
Slimes dosen't spawn on my singleplayer word in slime chunks. Tried in multiple chunks, multiple times, for a week now. Still not a single slime spawned. The world was generated in the early snapshots of Minecraft Java edition 1.14
In my testing I applied a glass roof and the rate appeared to have at least halved. Efficiency of a farm isn't the problem. I usually create a farm close to my base, passively generating slime and letting their own pathing algorithm remove them from the platforms. Now, to get any rates similar to 1.12 and 1.13, I have to create a hole, which I don't want near my base. Since its not near my base, i have to afk at it. As a casual player who wants to build a design using slime, but i am required to build a farm that would take 6 hrs compared to an hour, I am not inspired to play.
Efficiency isn't the problem when the spawning algorithm has changed, making spawn rates negligible unless you are trying to make a efficient design.
Alright, I have edited this ticket so that it actually includes that blocks above the spawning platform decrease the spawning frequency immensely, and I was able to confirm that.
While killing all other mobs that were spawning, in the slime chunk with no roof, 18707 slimes spawned, while in the one with a bunch of blocks above it, only 1369 spawned.
I repeated the experiment with glass instead of sandstone above the chunk with a roof, and here the numbers were similar (18082 without roof, and 1307 with glass above).
This is WAI. Since light went to its own thread, spawn algorithm uses a different heightmap to determine topmost spawnable block as the top block that is not air, rather than top block that is not transparent. There is no other heightmap that the spawning algorithm could currently use. That change was deliberate and intended. Just remove all the blocks above your farms and not worry about it.
Yes. The question is only, is it intentional that slimes have become way more rare than previously or is it an unintentional side effect of those changes? Of course the new behaviour can be explained with the new lighting engine from 1.14, but that doesn't mean that slimes underground were supposed to become rarer.
Cannot reproduce, slimes do spawn underground just fine for me