From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: BillyGalbreath 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 --- 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 - Fix MC-4; diff on change } @VisibleForTesting static double decode(long value) { - return (double)value / 4096.0D; + return (double)value / 4096.0D; // Paper - Fix MC-4; 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 180f87a67c84fc0cf3f54755da9801365d4158f8..9085eeffaa7b50e5e59a794d0323cae83248f242 100644 --- a/src/main/java/net/minecraft/world/entity/Entity.java +++ b/src/main/java/net/minecraft/world/entity/Entity.java @@ -4286,6 +4286,16 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource, S 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);