[MC-65065] Content of Minecart with Spawner is not sent to the client

The bug

The mob inside a minecart with spawner is never rendered, even if the spawner is customized.

How to reproduce

Summon a minecart with spawner that spawns mobs. The steps below show how to do this without hardcoding any spawner data.

```
/setblock ~2 ~2 ~ spawner
```

/summon minecraft:spawner_minecart ~2 ~ ~

```
/give @s minecraft:blaze_spawn_egg
```
```
/tick freeze
```
Right-click the spawner with the spawn egg (you cannot do the same to the minecart due to MC-110427)

/data modify entity @n[type=minecraft:spawner_minecart] {} merge from block ~2 ~2 ~

Break the floating spawner block
```
/tick unfreeze
```
❌ Observe that despite the complete absence of visual indication that the spawner minecart is doing anything, it will (after a significant delay) spawn blazes as expected

Note

Note that since 15w33a, no miniature is rendered at all; prior to this verison, a pig was rendered. The attached screenshot is from before 15w33a.

Code analysis

Code analysis by @unknown can be found in this comment.

Linked issues

is duplicated by 3

MC-9326 Spawner cart showing wrong spinning entity Resolved

MC-110426 Minecart with Spawner doesn't show mob inside it Resolved

MC-198252 Minecart with spawner doesn't have a mob inside it. Resolved

relates to 2

MC-66894 Spawner minecarts displayed mob/particle is offset Reopened

MC-267107 Spawners unsuccessfully try to summon hostile entities on peaceful difficulty Resolved

Attachments

MC-65065.mp4

Comments 28

Anon Ymus 2014-08-02T20:47:17Z

Please add steps to reproduce.

Qwert225 2014-08-04T11:17:04Z

I spawned this minecart with spawner using summon command. It spawns mobs correctly, but mob miniature is incorrect (pig instead of skeleton). Effect of this bug is only visual, it does not affect spawning.

Bug affects all minecarts with spawner in 1.7.2. Tested with 5 types of mobs, always the same result (pig miniature inside the spawner).

onnowhere 2014-08-13T16:42:44Z

I can confirm this for 14w32d, though the pig is also off centered now

onnowhere 2014-08-25T17:30:15Z

Still in pre2

Qwert225 2014-09-04T21:18:27Z

Confirmed for 1.8

18 more comments

marcono1234 2015-05-25T19:36:39Z

Confirmed for

1.8.5
1.8.6

The rotation also doesn't stop if the player gets out of range

onnowhere 2015-09-17T22:27:31Z

In the latest snapshots, not sure which one, the entity seems to have disappeared completely?

tatsu 2015-11-25T08:20:48Z

Confirmed for 15w47c

marcono1234 2015-12-12T13:17:33Z

Confirmed for

15w50a No entity is displayed at all, probably because of the "fix" of MC-66894

The reason for that is, that the func_151260_c() method in the /Client/src/net/minecraft/entity/EntityTrackerEntry.java class (MCP 1.8 names) sends a S0EPacketSpawnObject packet for minecarts. This packet is only able to store one additional integer for special information. However for minecarts this integer is used to represent the minecart type. This means the client does not get the information about which mob is visible.

private Packet func_151260_c()
{
	if (this.trackedEntity instanceof EntityItem)
	{
		//...
	}
	
	//...
	
	else if (this.trackedEntity instanceof EntityMinecart)
	{
		EntityMinecart var9 = (EntityMinecart)this.trackedEntity;
		return new S0EPacketSpawnObject(this.trackedEntity, 10, var9.func_180456_s().func_180039_a());
	}
	
	//...
}

One way to "fix" this would be to override the method NBTTagCompound func_174819_aU() in the /Client/src/net/minecraft/entity/ai/EntityMinecartMobSpawner.java class to either return all NBT data or only the entity to spawn. As updating packets are not send every tick, it might be better to send all the data to make sure the displayed mob changes at the right point for the client. This would also require to add code to the func_174834_g(NBTTagCompound p_174834_1_) method in the /Client/src/net/minecraft/entity/Entity.java class to just call the readEntityFromNBT(NBTTagCompound tagCompund) method. Or adding a data watcher for these fields might work as well, but I am not too familiar with how they work.

SunCat 2016-02-19T13:13:51Z

There is no entity in spawner minecart for 1.9-pre2

bob 2016-11-06T11:11:32Z

Is this still an issue in the latest snapshot 16w44a? If so please update the affected versions.

This is an automated comment on any open or reopened issue with out-of-date affected versions.

wobst.michael 2020-02-16T10:31:05Z

Currently this cannot be reproduced due to being blocked by MC-110426.

pokechu22 2020-02-16T22:40:59Z

After some more investigation, I've decided that MC-110426 should be merged into this ticket. The actual difference that caused the mob to stop rendering is mundane: Mojang removed the call to TileEntityMobSpawnerRenderer.renderMob(minecart.func_98039_d(), minecart.posX, minecart.posY, minecart.posZ, partialTicks) in RenderMinecartMobSpawner in 15w33a (for 1.9; it exists in 15w32c). The underlying issue of the mob inside not being sent to the client still exists, and could be fixed nowadays with NBT entity metadata (as is done with parrots on players). Were the rendering to be re-enabled without fixing the syncing, the pig issue would resurface. This ticket already listed versions where the mob didn't render for a few versions, so it is bit more confusing to try to keep them separate.

pulpetti 2020-07-21T14:37:43Z

In 1.16.1 and 20w29a