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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: BillyGalbreath <blake.galbreath@gmail.com>
Date: Tue, 8 Dec 2020 20:24:52 -0600
Subject: [PATCH] MC-4: Fix item position desync
This fixes item position desync (MC-4) by running the item coordinates
through the encode/decode methods of the packet that causes the precision
loss, which forces the server to lose the same precision as the client
keeping them in sync.
diff --git a/src/main/java/net/minecraft/network/protocol/game/VecDeltaCodec.java b/src/main/java/net/minecraft/network/protocol/game/VecDeltaCodec.java
index 5ca3ad7b3d7606accd0a58b3c708fadb349608f7..4b6e0fe2fabcc55007fd8979e81f66df9c0278b7 100644
--- a/src/main/java/net/minecraft/network/protocol/game/VecDeltaCodec.java
+++ b/src/main/java/net/minecraft/network/protocol/game/VecDeltaCodec.java
@@ -9,12 +9,12 @@ public class VecDeltaCodec {
@VisibleForTesting
static long encode(double value) {
- return Math.round(value * 4096.0D);
+ return Math.round(value * 4096.0D); // Paper - diff on change
}
@VisibleForTesting
static double decode(long value) {
- return (double)value / 4096.0D;
+ return (double)value / 4096.0D; // Paper - diff on change
}
public Vec3 decode(long x, long y, long z) {
diff --git a/src/main/java/net/minecraft/world/entity/Entity.java b/src/main/java/net/minecraft/world/entity/Entity.java
index 2e5a20e65a7475d39c789b89955dfa06d5923b53..e5dc024ac2dcb39ccc4f72b90e0f9b9000dd818d 100644
--- a/src/main/java/net/minecraft/world/entity/Entity.java
+++ b/src/main/java/net/minecraft/world/entity/Entity.java
@@ -4232,6 +4232,16 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
return;
}
// Paper end - rewrite chunk system
+ // Paper start - fix MC-4
+ if (this instanceof ItemEntity) {
+ if (io.papermc.paper.configuration.GlobalConfiguration.get().misc.fixEntityPositionDesync) {
+ // encode/decode from ClientboundMoveEntityPacket
+ x = Mth.lfloor(x * 4096.0D) * (1 / 4096.0D);
+ y = Mth.lfloor(y * 4096.0D) * (1 / 4096.0D);
+ z = Mth.lfloor(z * 4096.0D) * (1 / 4096.0D);
+ }
+ }
+ // Paper end - fix MC-4
if (this.position.x != x || this.position.y != y || this.position.z != z) {
this.position = new Vec3(x, y, z);
int i = Mth.floor(x);
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