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F7 is not showing where mobs can spawn properly


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When F7 is pressed, it shows Xs on the ground to show where mobs are able to spawn, and getting rid of the X should make it so mobs can no longer spawn, except mobs are STILL spawning, and in the location where they do, the Block Light is 7, but no X has appeared. (I don't know what mod it is that gives this capability, but would updating it possibly fix the issue?)

I just watched a Zombie spawn next to the spawner, when there were no Yellow or Red Xs.

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Don't some mobs spawn in light 7 or less? Could the issue just be that 1 light level?

Most mobs spawn on that level. The issue is that the X is not showing they will spawn there, when it should.


I don't know which it is either.  I think it could be NEI... but I don't know.  You could probably report it anyway.

Yeah, I'll do just that.

I just posted here first, in case it wasn't a bug, and I was just crazy.

Edited by Tehcero
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Some quick poking around in creative suggests it's working just fine.


That said, spawner blocks are special. They skip a number of checks over ambient spawning; in particular, they don't check for a solid block beneath a potential spawn location. This can cause mobs to spawn in midair in a room that mobs wouldn't normally be able to spawn in; if they're not flyers such as bats, gravity will immediately take effect and bring them back down to the ground, making them appear to spawn in invalid locations.


For example, if all your torches are on the ground, and there is a block at floor level at light level 8 within range, then F7 will show no X; however, since all your torches are on the ground, the block immediately above that is at light level 7; if the block above that is open space, then that is a valid spawn location for a spawner block, but not ambient spawning (because of the solid ground check), and therefore no X is shown.


-E- Oh right, F3 shows the light level at EYE level, not floor level. You need to add or subtract 1 (depending on what direction the nearest light is in) to get the floor level light, which is what mob spawning checks.

Edited by roothorick
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