I've created a custom hanging entity that I want to use to replace the ItemFrame so that I can supply some additional logic.

 

However, I have a couple issues.

If I don't register the mod entity, then the entity shows up and behaves normally, except that it doesn't save (this makes sense: there's no entity ID mapping for it).  However, if I add the registerModEntity line for it, then it doesn't show up in-game at all () but does save (as well as popping off if the block it's attached to is broken).

 

Main mod class:

			itemFrameReplacement = new ItemItemFrame();
	itemFrameReplacement.setRegistryName(new ResourceLocation("minecraft","item_frame"));
	itemFrameReplacement.setUnlocalizedName("frame");
	try {
		GameRegistry.addSubstitutionAlias("minecraft:item_frame", Type.ITEM, itemFrameReplacement);
	} catch (ExistingSubstitutionException e) {
		e.printStackTrace();
	}
	//commenting this line changes behavior:
	EntityRegistry.registerModEntity(EntityItemFrameReplacement.class, "item_frame_rep", 0, this, 48, 10, false);

If you look at

EntityTrackerEntry::createSpawnPacket

you will see that item frames use a specialized spawn packet, which uses a special constructor to set the positional data. FMLs spawn mechanic doesn't do this and you have to emulate it using

IEntityAdditionalSpawnData

.

 

Ahh. I wouldn't have even thought to look there.

Thanks.

As there are very few posts about IEntityAdditionalSpawnData...

(Not that it was hard, but having the reference is nice!)

 

Make the custom entity implement it and then write this:

 

	@Override
public void writeSpawnData(ByteBuf buffer) {
	BlockPos p = getHangingPosition();
	buffer.writeInt(p.getX());
	buffer.writeInt(p.getY());
	buffer.writeInt(p.getZ());
	buffer.writeInt(this.getHorizontalFacing().getIndex());
}

@Override
public void readSpawnData(ByteBuf buffer) {
	BlockPos p = new BlockPos(buffer.readInt(),buffer.readInt(),buffer.readInt());
	this.hangingPosition = p;
	int f = buffer.readInt();
	updateFacingWithBoundingBox(EnumFacing.values()[f]);
}

Just as a note, you can encode a

BlockPos

more easily and efficiently using either the method in

PacketBuffer

or

BlockPos::toLong

resp.

BlockPos.fromLong

.

If you use

PacketBuffer

that also has methods

readEnumValue

and

writeEnumValue

for maximum convenience

 

I wondered about that with the BlockPos, I hadn't seen anywhere a good way to encode it in packets (and vanilla decomposes it, or at least does for SPacketSpawnObject packet; see line 58).  Also, good to know about the read/write enum values.  Much handy.

 

Makes things

	@Override
public void writeSpawnData(ByteBuf buffer) {
	PacketBuffer pack = new PacketBuffer(buffer);
	pack.writeBlockPos(getHangingPosition());
	pack.writeEnumValue(this.getHorizontalFacing());
}

@Override
public void readSpawnData(ByteBuf buffer) {
	PacketBuffer pack = new PacketBuffer(buffer);
	hangingPosition = pack.readBlockPos();
	updateFacingWithBoundingBox(pack.readEnumValue(EnumFacing.class));
}

PacketBuffer

also has

readBlockPos

/

writeBlockPos

 

Oh, you put "or" and I read it as "and."  Thanks diesieben07.