MC-113981All mobs require two non-full cube blocks to be spawned even if the mob is not two blocks tall
The bug
All mobs require two non-full blocks to be spawned naturally even if the mob is only one block tall.
How to reproduce
- Create a Superflat world with the following preset
minecraft:stone,minecraft:air,minecraft:stone,minecraft:stone_slab
- Use for example the /say command to list all entities
/say @e[type=!player]
→ No entity is listed
- Replace some blocks with non-full cube blocks like slabs
/fill ~ ~-1 ~ ~170 ~-1 ~170 stone_slab
Note how the available space is still one air block, but now the block above it is a non-full block (stone slab) - Use the /say command again
/say @e[type=!player]
→ Bats and spiders are listed
Code analysis
Based on 1.11.2 decompiled using MCP 9.35 rc1
The method net.minecraft.world.WorldEntitySpawner.canCreatureTypeSpawnAtLocation(SpawnPlacementType, World, BlockPos) tests for all mobs for two non-full cube blocks, regardless of the mob size. The same applies to water mobs in this method as well.
Attachments1
Created Issue:
All mobs require two non-full cube blocks to be spawned even if the mob is not two blocks tall
The bug
All mobs require two non-full blocks to be spawned naturally even if the mob is only one block tall.
How to reproduce
- Create a Superflat world with the following preset
3;minecraft:stone,minecraft:air,minecraft:stone,minecraft:stone_slab;1;- Use for example the /say command to list all entities
/say @e[type=!player]→ No entity is listed
- Replace some blocks with non-full cube blocks like slabs
/fill ~ ~-2 ~ ~170 ~-2 ~170 stone_slab- Use the /say command again
/say @e[type=!player]→ Bats and spiders are listed
Code analysis
Based on 1.11.2 decompiled using MCP 9.35 rc1
The method net.minecraft.world.WorldEntitySpawner.canCreatureTypeSpawnAtLocation(SpawnPlacementType, World, BlockPos) tests for all mobs for two non-full cube blocks, regardless of the mob size. The same applies to water mobs in this method as well.
![[Mod] Michael Wobst](../../../data/avatars/users/37868.png){kind=small}
![[Mojang] Nathan Adams](../../../data/assets/gravatar/dinnerbone.png){kind=small}
![[Helper] gaspoweredpick](../../../data/avatars/users/80904.png){kind=small}
![[Mod] LateLag](../../../data/avatars/users/92884.png){kind=small}
The bug
All mobs require two non-full blocks to be spawned naturally even if the mob is only one block tall.
How to reproduce
- Create a Superflat world with the following preset
3;minecraft:stone,minecraft:air,minecraft:stone,minecraft:stone_slab;1;- Use for example the /say command to list all entities
/say @e[type=!player]→ No entity is listed
- Replace some blocks with non-full cube blocks like slabs
/fill ~ ~-2~ ~170 ~-2~170 stone_slab- Use the /say command again
/say @e[type=!player]→ Bats and spiders are listed
Code analysis
Based on 1.11.2 decompiled using MCP 9.35 rc1
The method net.minecraft.world.WorldEntitySpawner.canCreatureTypeSpawnAtLocation(SpawnPlacementType, World, BlockPos) tests for all mobs for two non-full cube blocks, regardless of the mob size. The same applies to water mobs in this method as well.
The bug
All mobs require two non-full blocks to be spawned naturally even if the mob is only one block tall.
How to reproduce
- Create a Superflat world with the following preset
minecraft:stone,minecraft:air,minecraft:stone,minecraft:stone_slab- Use for example the /say command to list all entities
/say @e[type=!player]→ No entity is listed
- Replace some blocks with non-full cube blocks like slabs
/fill ~ ~-1 ~ ~170 ~-1 ~170 stone_slab
- Use the /say command again
/say @e[type=!player]→ Bats and spiders are listed
Code analysis
Based on 1.11.2 decompiled using MCP 9.35 rc1
The method net.minecraft.world.WorldEntitySpawner.canCreatureTypeSpawnAtLocation(SpawnPlacementType, World, BlockPos) tests for all mobs for two non-full cube blocks, regardless of the mob size. The same applies to water mobs in this method as well.
![[Mod] Jiingy](../../../data/avatars/users/91802.png){kind=small}
At first I thought this was related to MC-113981, but it looks like it isn't since that ticket states that mobs will spawn with slabs/etc set as the second block above a block of air. Other than that I haven't been able to locate any tickets that resemble my issue
Sadly there is no easy way to test this, as Superflat "minecraft:bedrock,2*minecraft:dirt,minecraft:grass_block,minecraft:air,minecraft:oak_trapdoor[half=top],minecraft:stone;minecraft:plains;village" doesn't seem to work (you can't specify which half) and the default position is bottom half.
However, you can fill a large area with top-half trapdoors of any type, which should allow for proper testing. This is what I did, and then I killed all non-player entities to check for spawns. Nothing, not even the spiders would spawn, despite the height being enough to allow for the spawn.
The test:
Create a superflat world
Settings: minecraft:bedrock,2*minecraft:dirt,minecraft:grass_block,2*minecraft:air,minecraft:stone;minecraft:plains;village
Once in the world, use the /fill command to place a bunch of top-half trapdoors in the headspace, which should allow for just over 1 3/4 blockspace for mobs to spawn. The larger the area the better.
use /kill @e[type=!player] to kill all the mobs, then again to kill the items.
Walk around, and look for any signs of mobs. They will only be present where you have two full blocks of airspace.
(Optional: Give yourself night vision like I did.)
this is a shame, as this used to be the only effective way to get only creepers to spawn (you'd limit the spawn location sizes via carpet to stop spiders).
EDIT
I loaded the world in the 1.13.1 Pre1, and it still holds true, except for bats (although they have a highly suppressed spawn rate still, compared to having 2 vertical air blocks.
Would MC-113981 describe your issue? While the glass is transparent, it is considered "full cube" unlike the slab.
Cannot reproduce for 1.13.1, seems to be fixed. Can anyone else reproduce?
Just tested the 1.13.1 preset, still seems to be an issue.
This also happens for bats, which doesn't make sense at all.
Can't reproduce in 1.18.1Can still reproduce this, however one of the reproduction steps was incorrect; I have fixed it now.