Brief note
As of 24w19b the command to repro is:
/summon minecraft:wither_skull ~ ~2 ~ {Motion:[0.0,0.0,0.5],acceleration_power:0.3}I will update the rest of this description later.
The bug
Wither skulls and small/dragon fireballs will stutter during flight if their power tag does not have a magnitude of either 0 or 0.1. Wind charges will do this as well, but this is less of an issue since they do not experience drag so a power of magnitude 0 is sufficient for most applications.
/summon minecraft:wither_skull ~ ~2 ~ {Motion:[0.0,0.0,0.5],power:[0.2d,0d,0d]}Details
The client assumes that wither skulls, wind charges and small/dragon fireballs have a power of magnitude 0.1 when calculating their acceleration, while on the server the value is stored properly. The only exception to this is when the magnitude is 0, in which case the entity behaves properly according it its Motion; I assume the acceleration calculation is either being skipped or doing nothing (as in Unity when Transform.LookAt receives the executor) in this case. The game will re-sync the entity's position every second or so, creating jerky movement for any affected entity whose power magnitude is not equal to 0 or 0.1.
Reloading the projectile will update power's direction on the client (if it has been modified with /data), but its magnitude will still be interpreted as 0.1 (unless it is 0). I imagine (and would hope that) any fix to the previous paragraph would fix this as well, although if not the devs are within their rights to call it WF and make me sad.
So to summarize, due to this bug, for a summoned projectile of this type to move smoothly it must be summoned with a power magnitude of either:
0, in which case it will experience drag (unless it is a wind charge) but can be redirected easily by modifying its
Motiontag (although the client will not receive this update until the next sync, which could be up to 1 second away, due to MC-139548).0.1, in which case it will quickly accelerate/decelerate (depending on its
Motion) to its (fixed) terminal velocity and can only redirected buglessly by having itspowermodified and then being reloaded.
Thoughts on a fix
It seems likely that when blaze fireballs were added to the game, they experienced drag, and that instead of disabling this drag whoever implemented them decided to add an acceleration field that would counteract it. This seems like a rather lazy solution, and I'm not surprised that its implementation is imperfect. A proper fix would get rid of the drag these projectiles naturally experience and do away with the power field; any in-flight trajectory changes can be accomplished through direct modification of the Motion tag, and should be communicated to the client immediately, as they are when a player punches a ghast fireball.
Linked issues
is duplicated by 2
relates to 3
Comments 19
Confirmed for
1.8.4
WitherSkulls and SmallFireballs with a direction tag like *direction:[0.5,0.0,0.0]* move very raggedly.
I don't know what you mean by "blue wither skulls".
Example command
/summon WitherSkull ~ ~2 ~ {direction:[0.0,0.0,0.5]}The wither can shoot two kinds of wither skulls- fast moving black ones and slow moving blue ones. The black ones cannot break cobblestone or harder blocks, while blue ones can.
Oh didn't knew that
However can you please add SmallFireballs as well in your text because they are also affected by the raggedly movement
Could you please change this report to "SmallFireballs and WitherSkulls move ragedly when summoned"? I put the fact that these blue WitherSkulls exist but can't be detected in MC-81656
Note: This does not affect Fireballs
A few more notes on this:
The example commands should be updated to use
Motioninstead ofdirectionsince that tag was removed some time ago.From what I'm able to tell, the client assumes all non-Ghast fireballs (including both types of wither skulls) have a
powerof magnitude 0.1 when calculating their acceleration, while on the server the value is stored properly. (If the magnitude is 0, the entity behaves properly according it itsMotion, so I assume the acceleration calculation is either being skipped or doing nothing (as in Unity when Transform.LookAt receives the executor) in this case.) The game will re-sync the entity's position every second or so, creating jerky movement for any affected entity whosepowermagnitude is not equal to 0 or 0.1.Reloading the projectile will update
power's direction on the client (if it has been modified with /data), but its magnitude will still be interpreted as 0.1 (unless it is 0). I imagine (and would hope that) any fix to bullet point 2 would fix this as well, although if not the devs are within their rights to call it WF and make me sad.
So to summarize, due to this bug, for a summoned non-Ghast fireball to move smoothly it must be summoned with a power magnitude of either:
0, in which case it will experience drag but can be redirected easily by modifying its Motion tag.
0.1, in which case it will quickly accelerate/decelerate (depending on its
Motion) to its (fixed) terminal velocity and can only redirected buglessly by having itspowermodified and then being reloaded.
Affects 22w07a. Here are some commands which use power instead of direction:
/summon minecraft:small_fireball ~ ~2 ~ {power:[0.2d,0d,0d]}
/summon minecraft:wither_skull ~ ~2 ~ {power:[0.2d,0d,0d]}Notice how changing 0.2 to 0.1 will fix the movement as per the above comment.
This was not fixed in 24w14a; only certain cases of wind charge stuttering (primarily covered by other tickets) were fixed. This ticket covers the stuttering that these projectiles experience one second after creation during normal gameplay, as well as stuttering that can only be reproduced through commands.
Please post your suggestions on reddit.