[MC-268716] Magma Cubes spawn even if there's only 2 blocks in height

Magma Cubes shouldn't spawn when there's only 2 blocks in height. This gets ignored and slows down almost every gold farm that uses magma blocks since they will now be able to spawn in them. Overtime, if you're afking at such gold farm the magma cubes will take up a large portion of the mob cap.

What I expected to happen was...:{*}{*}

They shouldn't be able to spawn when there's only 2 blocks in height,

What actually happened was...:

They spawn even though there's only 2 blocks in height.

Steps to Reproduce:
1. Build a huge magma block platform in a nether wastes biome.
2. Build a glass platform 2 blocks above it that completely covers it. (This should now in theory prevent ghasts and magma cubes from spawning. Ghasts do not spawn, but magma cubes do.)
3. Place a chain chommand block which kills Zombified Piglins and activate it.

4. Fly a decent bit above the farm and watch the magma cubes spawn. Since we are using a transparent block as top layer they will clip through it when they spawn.

Linked issues

is duplicated by 1

MC-268983 Magma Cubes spawn in too small spaces (smaller than 3 x 2.1 x 3 block) Resolved

relates to 1

MC-268627 Slime spawns are incorrect Resolved

Attachments

Comments 5

[Mod] Jingy 2024-03-01T19:37:31Z

Can confirm in 24w09a. I've written easier steps to follow to reproduce and confirm this:

Run the following command to enter the nether (if in the overworld)
```
/setblock ~ ~ ~ minecraft:nether_portal
```
Locate a nether wastes biome, teleport to it
```
/locate biome minecraft:nether_wastes
```
Starting flying, run the following command
```
/tp ~ 190 ~
```

Build spawning platforms

/fill ~30 ~ ~30 ~-30 ~ ~-30 glass
/fill ~30 ~-3 ~30 ~-30 ~-3 ~-30 minecraft:magma_block

Fly above the farm to allow for magma cubes to spawn

capfan 2024-03-13T15:52:00Z

I can still duplicate the issue in 24w10a

Edit: Still happening in 24w11a

Arisa Bot 2024-03-20T13:32:20Z

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Kerwin 2024-03-27T10:05:31Z

@panda4994 💪🏼

NandyCippi 2024-06-06T04:39:53Z

Issue persists in 1.21 Pre-Release 3 and it manifests in the behavior of both Magma Cubes and Slimes. When adequate space is available for a size 0 slime to spawn, all naturally occurring slimes of varying sizes will instead spawn at that location.

Here's a step-by-step guide to reproduce the undesired behavior:

Launch a super flat world in Minecraft version 1.21 Pre-release 3.
Locate a designated slime chunk within the world.
Summon end crystals in the designated area, positioning them precisely 0.52 blocks above the ground.
Move between 24 and 128 blocks away from the slime chunk.
Observe the spawning of slimes of sizes 0, 1, and 3 within the specified area

For further investigation, repeat the process with the end crystals positioned 0.5 blocks above the terrain surface. Note the absence of slime spawns within the designated region when the end crystals are placed at this height.

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