Paper/patches/server/0474-MC-4-Fix-item-position-desync.patch

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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 05ac41e136da43284fb24a6b698ebd36318278fb..3c4ac79c094dc2fff7de94150a34b7bf814ac0de 100644
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--- a/src/main/java/net/minecraft/network/protocol/game/VecDeltaCodec.java
+++ b/src/main/java/net/minecraft/network/protocol/game/VecDeltaCodec.java
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@@ -9,12 +9,12 @@ public class VecDeltaCodec {
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@VisibleForTesting
static long encode(double value) {
- return Math.round(value * 4096.0D);
+ return Math.round(value * 4096.0D); // Paper - Fix MC-4; diff on change
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}
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@VisibleForTesting
static double decode(long value) {
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- return (double)value / 4096.0D;
+ return (double)value / 4096.0D; // Paper - Fix MC-4; diff on change
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}
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 55395837df277eac393949aa7447d69e57c5d756..da5dcea43fdbc0ad0acb1130d363cc8cbea16dfa 100644
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--- a/src/main/java/net/minecraft/world/entity/Entity.java
+++ b/src/main/java/net/minecraft/world/entity/Entity.java
@@ -4167,6 +4167,16 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource, S
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return;
}
// Paper end - Block invalid positions and bounding box
+ // Paper start - Fix MC-4
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+ if (this instanceof ItemEntity) {
+ if (io.papermc.paper.configuration.GlobalConfiguration.get().misc.fixEntityPositionDesync) {
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+ // encode/decode from ClientboundMoveEntityPacket
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+ 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
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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);