MCPE-106860Ghast fireball damage goes through cobblestone bottom slabs
A ghast fireball that hits a roof made of (bottom) cobblestone slabs can do damage on the other side of the slab, even though it does no damage to the slabs themselves. That is, if a ghast fireball impacts such a roof, the contents of the room beneath it can sustain blast damage even if the roof is left intact.
This has been confirmed with cobblestone slabs (stone_slab), andesite slabs (stone_slab3) and stone slabs (stone_slab4), so presumably the bug affects every kind of stone bottom slab.
Top slabs (upper slabs) do not manifest this bug. Neither do full-size stone blocks.
Other sources of explosions also apparently do not manifest this bug (tested with TNT, beds in the Nether, and end crystals).
Steps to reproduce:
- Import and open the updated attached world MCPE-106860.mcworld. You will find yourself in front of a button labeled Start with a stairway to its left and a room to the left of that with a ceiling consisting of cobblestone bottom slabs and a layer of orange stained glass below that.
- Press the Start button. This repairs the ceiling (in case it is damaged from a previous test) and applies strong, long-lasting Regeneration and Fire Resistance effects to you.
- Go up the stairs and out onto the roof. You will see two ghasts above you. Note: If either of the ghasts is missing, there is a button at the top of the stairs that will respawn it.
- Move around the roof, especially into the corners, for 10–20 seconds while the ghasts shoot fireballs at you.
- Go back inside, down the stairs and into the room. Examine the ceiling for missing glass blocks. If there are none the first time, repeat from step 2.
Expected result:
There are no glass blocks missing under the ceiling because cobblestone blocks are resistant to blast damage from ghast fireballs.
Actual result:
Some of the glass blocks were destroyed by fireballs even though the slabs are all intact.
Original Description:
I have a netherrack cooking facility and a collocated netherwort farm in the nether. The building is made of netherbrick and is fully enclosed. It is roofed with cobblestone slabs. I often hunt ghasts from the roof while cooking netherrack and waiting for a new crop of netherwort to grow. Ghasts are firing at me, hitting the roof and tearing up the netherwort that is 4 blocks below.
Linked Issues
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Created Issue:
Ghasts aree shooting through slabs
I have a netherrack cooking facility and a collocated netherwort farm in the nether. The building is made of netherbrick and is fully enclosed. It is roofed with cobblestone slabs. I often hunt ghasts from the roof while cooking netherrack and waiting for a new crop of netherwort to grow. Ghasts are firing at me, hitting the roof and tearing up the netherwort that is 4 blocks below.
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![[Bot] Arisa](../../../data/avatars/users/43007.png){kind=small}
MCPE-106860.mcworld
Original Description:
I have a netherrack cooking facility and a collocated netherwort farm in the nether. The building is made of netherbrick and is fully enclosed. It is roofed with cobblestone slabs. I often hunt ghasts from the roof while cooking netherrack and waiting for a new crop of netherwort to grow. Ghasts are firing at me, hitting the roof and tearing up the netherwort that is 4 blocks below.
Ghasts aree shooting throughslabsGhast fireball damage goes through stone bottom slabs
Original Description:
I have a netherrack cooking facility and a collocated netherwort farm in the nether. The building is made of netherbrick and is fully enclosed. It is roofed with cobblestone slabs. I often hunt ghasts from the roof while cooking netherrack and waiting for a new crop of netherwort to grow. Ghasts are firing at me, hitting the roof and tearing up the netherwort that is 4 blocks below.
A ghast fireball that hits a roof made of (bottom) stone slabs can do damage on the other side of the slab, even if it does no damage to the slabs themselves. That is, if a ghast fireball impacts such a roof, the contents of the room beneath it can sustain blast damage even if the roof is left intact.
This has been confirmed with cobblestone slabs (stone_slab), andesite slabs (stone_slab3) and stone slabs (stone_slab4), so presumably the bug affects every kind of stone bottom slab.
Top slabs (upper slabs) do not manifest this bug. Neither do full-size stone blocks.
Other sources of explosions also apparently do not manifest this bug (tested with TNT, beds in the Nether, and end crystals).
Steps to reproduce:
(A demo world is attached.)
- In the Nether, build a structure with blast resistant walls and give it a roof of cobblestone bottom slabs.
- Fill the layer below the roof with blocks that have low to moderate blast resistance.
- Go onto the roof in survival mode and lure a ghast to shoot a fireball at you. Step aside to allow it to strike the roof instead.
- Examine the low-resistance layer in the room.
Expected result:
Wherever the roof was left intact, the fragile layer below it is also intact.Actual result:
Sometimes the fragile layer is damaged even though the roof above it isn't.Note:
MCPE-29200fixed a bug whereby ghast fireballs could destroy cobblestone slabs and walls. It's possible that the fix was incomplete in that it prevented the damage to the cobblestone but didn't stop the logic that follows the propagation of blast damage through it.Original Description:
I have a netherrack cooking facility and a collocated netherwort farm in the nether. The building is made of netherbrick and is fully enclosed. It is roofed with cobblestone slabs. I often hunt ghasts from the roof while cooking netherrack and waiting for a new crop of netherwort to grow. Ghasts are firing at me, hitting the roof and tearing up the netherwort that is 4 blocks below.
![[MCQA] Kinga Izdebska](../../../data/avatars/users/18949.svg){kind=small}
relates to
relates to
Ghast fireball damage goes through cobblestone bottom slabs
A ghast fireball that hits a roof made of (bottom) stone slabs can do damage on the other side of the slab, even
ifit does no damage to the slabs themselves. That is, if a ghast fireball impacts such a roof, the contents of the room beneath it can sustain blast damage even if the roof is left intact.This has been confirmed with cobblestone slabs (stone_slab), andesite slabs (stone_slab3) and stone slabs (stone_slab4), so presumably the bug affects every kind of stone bottom slab.
Top slabs (upper slabs) do not manifest this bug. Neither do full-size stone blocks.
Other sources of explosions also apparently do not manifest this bug (tested with TNT, beds in the Nether, and end crystals).
Steps to reproduce:
(A demo world is attached.)
- In the Nether, build a structure with blast resistant walls and give it a roof of cobblestone bottom slabs.
- Fill the layer below the roof with blocks that have low to moderate blast resistance.
- Go onto the roof in survival mode and lure a ghast to shoot a fireball at you. Step aside to allow it to strike the roof instead.
Examine the low-resistance layer in the room.Expected result:
Wherever the roof was left intact, the fragile layerbelow it is also intact.Actual result:
Sometimes the fragile layer is damaged even though the roof above it isn't.Note:
MCPE-29200fixed a bug wherebyghast fireballs could destroy cobblestone slabs and walls. It's possible that the fix was incomplete in that it prevented the damage to the cobblestone but didn't stop the logic that follows the propagation of blast damage through it.Original Description:
I have a netherrack cooking facility and a collocated netherwort farm in the nether. The building is made of netherbrick and is fully enclosed. It is roofed with cobblestone slabs. I often hunt ghasts from the roof while cooking netherrack and waiting for a new crop of netherwort to grow. Ghasts are firing at me, hitting the roof and tearing up the netherwort that is 4 blocks below.
A ghast fireball that hits a roof made of (bottom) cobblestone slabs can do damage on the other side of the slab, even though it does no damage to the slabs themselves. That is, if a ghast fireball impacts such a roof, the contents of the room beneath it can sustain blast damage even if the roof is left intact.
This has been confirmed with cobblestone slabs (stone_slab), andesite slabs (stone_slab3) and stone slabs (stone_slab4), so presumably the bug affects every kind of stone bottom slab.
Top slabs (upper slabs) do not manifest this bug. Neither do full-size stone blocks.
Other sources of explosions also apparently do not manifest this bug (tested with TNT, beds in the Nether, and end crystals).
Steps to reproduce:
- Import and open the updated attached world MCPE-106860.mcworld. You will find yourself in front of a button labeled Start with a stairway to its left and a room to the left of that with a ceiling consisting of cobblestone bottom slabs and a layer of orange stained glass below that.
- Press the Start button. This repairs the ceiling (in case it is damaged from a previous test) and applies strong, long-lasting Regeneration and Fire Resistance effects to you.
- Go up the stairs and out onto the roof. You will see two ghasts above you.
- Move around the roof, especially into the corners, for 10–20 seconds while the ghasts shoot fireballs at you.
- Go back inside, down the stairs and into the room. Examine the ceiling for missing glass blocks. If there are none the first time, repeat from step 2.
Expected result:
There are no glass blocks missing under the ceiling because cobblestone blocks are resistant to blast damage from ghast fireballs.Actual result:
Some of the glass blocks were destroyed by fireballs even though the slabs are all intact.Original Description:
I have a netherrack cooking facility and a collocated netherwort farm in the nether. The building is made of netherbrick and is fully enclosed. It is roofed with cobblestone slabs. I often hunt ghasts from the roof while cooking netherrack and waiting for a new crop of netherwort to grow. Ghasts are firing at me, hitting the roof and tearing up the netherwort that is 4 blocks below.
A ghast fireball that hits a roof made of (bottom) cobblestone slabs can do damage on the other side of the slab, even though it does no damage to the slabs themselves. That is, if a ghast fireball impacts such a roof, the contents of the room beneath it can sustain blast damage even if the roof is left intact.
This has been confirmed with cobblestone slabs (stone_slab), andesite slabs (stone_slab3) and stone slabs (stone_slab4), so presumably the bug affects every kind of stone bottom slab.
Top slabs (upper slabs) do not manifest this bug. Neither do full-size stone blocks.
Other sources of explosions also apparently do not manifest this bug (tested with TNT, beds in the Nether, and end crystals).
Steps to reproduce:
- Import and open the updated attached world MCPE-106860.mcworld. You will find yourself in front of a button labeled Start with a stairway to its left and a room to the left of that with a ceiling consisting of cobblestone bottom slabs and a layer of orange stained glass below that.
- Press the Start button. This repairs the ceiling (in case it is damaged from a previous test) and applies strong, long-lasting Regeneration and Fire Resistance effects to you.
- Go up the stairs and out onto the roof. You will see two ghasts above you. Note: If either of the ghasts is missing, there is a button at the top of the stairs that will respawn it.
- Move around the roof, especially into the corners, for 10–20 seconds while the ghasts shoot fireballs at you.
- Go back inside, down the stairs and into the room. Examine the ceiling for missing glass blocks. If there are none the first time, repeat from step 2.
Expected result:
There are no glass blocks missing under the ceiling because cobblestone blocks are resistant to blast damage from ghast fireballs.Actual result:
Some of the glass blocks were destroyed by fireballs even though the slabs are all intact.Original Description:
I have a netherrack cooking facility and a collocated netherwort farm in the nether. The building is made of netherbrick and is fully enclosed. It is roofed with cobblestone slabs. I often hunt ghasts from the roof while cooking netherrack and waiting for a new crop of netherwort to grow. Ghasts are firing at me, hitting the roof and tearing up the netherwort that is 4 blocks below.
![[Mod] Jarl-Penguin](../../../data/avatars/users/92849.png){kind=small}
A ghast fireball that hits a roof made of (bottom) cobblestone slabs can do damage on the other side of the slab, even though it does no damage to the slabs themselves. That is, if a ghast fireball impacts such a roof, the contents of the room beneath it can sustain blast damage even if the roof is left intact.
This has been confirmed with cobblestone slabs (stone_slab), andesite slabs (stone_slab3) and stone slabs (stone_slab4), so presumably the bug affects every kind of stone bottom slab.
Top slabs (upper slabs) do not manifest this bug. Neither do full-size stone blocks.
Other sources of explosions also apparently do not manifest this bug (tested with TNT, beds in the Nether, and end crystals).
Steps to reproduce:
- Import and open the updated attached world MCPE-106860.mcworld. You will find yourself in front of a button labeled Start with a stairway to its left and a room to the left of that with a ceiling consisting of cobblestone bottom slabs and a layer of orange stained glass below that.
- Press the Start button. This repairs the ceiling (in case it is damaged from a previous test) and applies strong, long-lasting Regeneration and Fire Resistance effects to you.
- Go up the stairs and out onto the roof. You will see two ghasts above you. Note: If either of the ghasts is missing, there is a button at the top of the stairs that will respawn it.
- Move around the roof, especially into the corners, for 10–20 seconds while the ghasts shoot fireballs at you.
- Go back inside, down the stairs and into the room. Examine the ceiling for missing glass blocks. If there are none the first time, repeat from step 2.
Expected result:
There are no glass blocks missing under the ceiling because cobblestone blocks are resistant to blast damage from ghast fireballs.
Actual result:
Some of the glass blocks were destroyed by fireballs even though the slabs are all intact.
Original Description:
I have a netherrack cooking facility and a collocated netherwort farm in the nether. The building is made of netherbrick and is fully enclosed. It is roofed with cobblestone slabs. I often hunt ghasts from the roof while cooking netherrack and waiting for a new crop of netherwort to grow. Ghasts are firing at me, hitting the roof and tearing up the netherwort that is 4 blocks below.
I was mistaken, this is not related to MCPE-31896. Indeed drowned do not even shoot tridents when within 3 blocks of their target.
The bug instead seems to be that the slab collision is not calculated correctly from certain angles. Both drowned and players can shoot tridents through upper slabs from underwater, and players can also break blocks behind upper slabs. Here are demonstrations:
Trident goes through slab.mp4
Player kills through slab 1.mp4
Player kills through slab 2.mp4
Drowned kills through slab.mp4
Break block behind slab while sinking.mp4
To interpret these videos it is important to note that the tridents that hit the mobs appear to hit well below the slabs and fall down below the slabs only because of MCPE-109423. That bug apparently extends their projectile hitbox in the direction of movement such that the hit registers while the center of the trident is still below the slab. However, that is not the cause of this bug. This bug is that the game allows the trajectory, not just the hitbox, of the projectile (or the player's block-breaking reach) to pass through the slab. The fact that tridents can pass through the slabs and lodge in the chest above the slab proves this. (If there are no blocks on the other side the trident flies through on a normal trajectory; while testing I launched one dozens of blocks past the chamber.)
EDIT: the crossed-out text above was based on an incorrect explanation of MCPE-109423. That bug is caused by the fact that when the game calculates a projectile hitting a mob, it keeps the projectile's position as its last ticked position instead of updating its position to the edge of the hit entity's collision box. Tridents move 4 blocks/tick, so they can "hit" and fall up to 4 blocks away from a mob.
Breaking blocks behind slabs is interesting because if there are no blocks within reach behind the slab then the slab can be broken as expected. This suggests that the game is offsetting the position of the slab's collision box.
The bug may only occur while moving upward or downward in water. I only had problems breaking slabs while allow myself to float instead of using flying to stand still.
I am not sure if this bug can be reproduced without waterlogging the slabs, or without the shooter being in water, as I only tested the reported scenario. However, I think this bug may have the same underlying cause as MCPE-106860, where ghast projectiles can pass through bottom slabs when shot from above. And snowballs fired by snow golems have reportedly exhibited some form of this behavior: MCPE-125598.
It's unclear from your description what you think the problem is. Please review the Issue Guidelines and provide us the steps to reproduce the issue, together with what the result was and what you expected.
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?? The issue is ghasts shooting through slabs. I have a building, it has a roof (cobblestone slabs), netherwort is growing inside the building. I have my bow out and make a sideline of potting at the gasbags while waiting for another crop to grow. The ghasts don't like me. They shoot back. I dodge and the fireball hits the roof.
What I would expect: The slabs would stop the fireball
What happens: At least part of the fireball is penetrating the slabs and tearing up my netherwort.
I hope this is clearer.
Ok, my mistake. I forgot for the moment that cobblestone is supposed to be blast resistant and I was imagining the fireballs were breaking the slabs, therefore penetrating to the interior, so I wasn't clear about what was wrong.
I need to try to reproduce this, but it might be sensitive to details like how the slabs are arranged and whether they're top or bottom slabs. It would be very helpful if you could provide a screenshot from which I could build something like what you have. Even better if you could upload a small world in which you can reproduce it yourself. Meanwhile, I'll play with it a little in case it's simply that cobblestone slabs aren't blast resistant at all (I think they ought to be, though).
I can confirm that the roof is indeed bottom slabs and is not itself being harmed by the fireballs but they or at least part of their damage is going through and damaging things below.
Thank you. This was submitted to the developers back in February after I found a way to reproduce it. I should have mentioned it in a comment at the time, but apparently I forgot.
This bug may have the same underlying cause as MCPE-155956. It seems that the calculation of slab collision allows certain trajectories or vectors that should be blocked to pass through. Here is one example from that report:
https://bugs.mojang.com/secure/attachment/492083/Trident%20goes%20through%20slab.mp4
I retested in 1.19.22 using the demo world. The demo world has two ghasts, one that shoots at a high angle to the surface, and one that shoots at a lower angle. The fireballs from either of them can, but don't always, break the glass below the slabs, so it would seem the trajectory angle isn't that important, but I can't rule out that some other property of the trajectory makes the difference, perhaps its length or direction.
Using a particle command in a repeating command block to mark the fireball's position, I have found that this issue occurs when the fireball gets ticked inside the top of the bottom slab's block space (the part that would be filled by a top slab). When this happens, the fireball gets ticked one more time on the the opposite side of the bottom slab, as if it had passed through, and the explosion center is set to that location. This happens even if there is only air on the other side of the slab, which implies that the game correctly identifies the slab as the impacted block. The bug is only that the location of the explosion is on the other side of the block. This issue is closely related to MCPE-160494: in both cases the expected behavior is that the position of the explosion would be at the leading edge of the block that the fireball impacts.