MC-64492Changes to mob spawning algorithm (Mobs don't require 'Air'-block for spawning cycle)
Previously, mobs did not spawn if there were no air blocks above the solid block chosen as the initial part of the spawn algorithm.
As of 14w25b snapshot, this is no longer the case. There is no obvious mention of such a change in the notes, hence filing this as a bug.
Creating a flat world with rail as the top surface results in no mobs spawning pre 14w25. From 14w25 and onwards, mobs will spawn despite the lack of completely clear spaces previously required to "seed" spawning.
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Changes to mob spawning algorithm
Previously, mobs did not spawn if there were no air blocks above the solid block chosen as the initial part of the spawn algorithm.
As of 14w25b snapshot, this is no longer the case. There is no obvious mention of such a change in the notes, hence filing this as a bug.
Creating a flat world with rail as the top surface results in no mobs spawning pre 14w25. From 14w25 and onwards, mobs will spawn despite the lack of completely clear spaces previously required to "seed" spawning.
Environment
Any
Changes to mob spawning algorithm (Mobs don't require 'Air'-block for spawning cycle)
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![[Mojang] Grum (Erik Broes)](../../../data/assets/gravatar/grum.png){kind=small}
![[Mojang] Jeb (Jens Bergensten)](../../../data/assets/gravatar/jeb.jpeg){kind=small}
[Mojang] Jeb (Jens Bergensten)A comment with security level 'global-moderators' was removed.
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![[Mod] Sonicwave](../../../data/avatars/users/94627.png){kind=small}
Duplicate of MC-64492 (occurs to all mobs, not just slimes).
Duplicate of MC-64492.
Probably duplicate (or related) to MC-64492.
Maybe duplicate/related to MC-64492.
Don't see a duplication of MC-64492, Slime blocks are solid, so the collision algorithm should work.
![[Mod] CubeTheThird](../../../data/assets/gravatar/cubethethird.jpeg){kind=small}
This is a direct result of the fix for MC-64492.
Sigh. Given the fact that MC-64492 as filed doesn't say anything about where mobs actually spawn (it's about where the pack can start trying to spawn) and the fix for it introduced new, different spawn restrictions without correcting the situation described in the report itself without any statement as to what was intended to be changed, I find it impossible to determine what is an intentional result of the fix for that bug and what is accidental. If you heard that it was intended from a Mojangsta you should say so, otherwise let's let a Mojangsta say whether it's "works as intended".
As I originally explained, it's entirely plausible that the intended result was to change "isOpaque" to "blocksMovement" (to prevent spawning within leaves, grass, cactus, and so on) and to add rails (the real new logic is more like !(!isSolidFullCube() && !canProvidePower() && !isLiquid() && !isAnyKindOfRail()) but I didn't want to get into all the extra detail to avoid confusing people), and the change to prevent spawning within a large number of redstone components was an unintentional "direct result" due to a mistake in refactoring the code.
I would also like to see confirmation from Mojang that it is intended that mobs no longer spawn on pressure plates. The fix for MC-64492 seems to be trying to revert to previous spawning behavior, whereas not spawning on pressure plates is new behavior, and breaks many popular farm designs. Mojang can of course change the game any way necessary, including breaking mob farms, but let it at least be intentional?
![[Mod] Torabi](../../../data/assets/gravatar/torabi.png){kind=small}
Was this fixed as a result of MC-64492 being fixed?
Confirmed for 1.8 (due to
MC-71518andMC-71008).This probably happend with the introduction of the Guardian. Hostile mobs now must be able to spawn inside water. So maybe the check for an Air-Block was simply removed and only the collision with objects remains.
if so, than it's sadly not a bug.
In 1.7, mobs could not spawn on a superflat world that had tallgrass (or any non-solid non-air block at the top). In 1.8 this changed, and they could.
The fix here in 15w46a appears to be that now 'rail' (and variants like golden_rail) do not allow mobs to spawn, but other non-solid blocks (like tallgrass and snow_layer) do. This is based on simple experiments in 15w46a with superflat worlds of varying top-layer blocks.
Further experiments show that on a world with a golden_rail top, a small patch of air will cause mobs to spawn only on the blocks without rail. So it's not just the air-seeding, it seems mobs cannot spawn naturally on rail (even rail with nearby air). Mobs from spawners still can spawn on rail.