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[1.7.2] Changing Entity Motion


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I have a tile entity that is changing the motion of certain entities around it, like snowballs. If I change the motionX/Y/Z of the snowball, the movement is pretty strange. First it goes like it should, then goes hyperspeed in the middle of flight(almost teleports) and then returns back to normal.


Is this a bug in vanilla minecraft/forge, or am I changing the motion incorrectly? This is basically all I'm doing:

entity.motionX = someForceVariable;

Any help is appreciated.

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After some experimenting, I also discovered that when I only push the entity on the client side(worldObj.isRemote), it goes the first half of the flight, and the opposite for the server.


I guess that means that without an isRemote or !isRemote check, the two are combined into one, so the snowball has to move quickly to get to the server bit after the client part is done, which explains the fast zone.

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Dude those diagrams are awesome, seriously!  I wish all posters were so clear about describing their problem :)


Sounds like you've run into a client-server synchronisation problem.  Anything you do to the entity on the client side will only last a short time until the server resynchronises it and your client changes are lost/overwritten.  There is a similar problem I wrestled with quite some time ago for EntityArrow http://www.minecraftforge.net/forum/index.php/topic,14315.msg73758.html#msg73758


Changes are often done to both the client and the server at the same time to reduce the apparent lag caused by packet transmission time, normally they stay in synch closely enough that when the resynch occurs the difference is small and you don't notice it.  It looks like there's something slightly different about Snowball so that when you push on both client and server, they have different effects so there is a big desynchronisation happening.  Unfortunately I don't know why that is.  The easiest fix might be to push the Entity on the server only and force a resynch (1.6.4 this was by sending Packet28 and/or Packet34, which will be slightly different in 1.7.2 but probably still very similar)




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After exploring some random classes, I found this piece of code:

WorldServer ws = (WorldServer) e.worldObj;
ws.getEntityTracker().func_151248_b(e, new S12PacketEntityVelocity(e));

Also, a method .func_151247_a() exists but has similar features. Unsure about which to use. After putting that after my push code, and inserting an !isRemote, the issue seemed to be fixed for long distances, but still exists if the snowball is close to the player.

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