From 5652259e1a219e368323bd729757fe386ec7f2de Mon Sep 17 00:00:00 2001 From: Spottedleaf Date: Tue, 20 Feb 2024 18:30:53 -0800 Subject: [PATCH] Fix entity tracker desync when new players are added to the tracker The delta position packet instructs the client to update the entity position by a position difference. However, this position difference is relative to the last position in the entity tracker state, not the last position which has been sent to the player. As a result, if the last position the player has recorded is different than the one stored in the entity tracker (which occurs when a new player is added to an existing entity tracker state) then the sent position difference will cause a position desync for the client. We can resolve this problem by either tracking the last position sent per-player, or by simply resetting the last sent position in the entity tracker state every time a new player is added. Resetting the last sent position every time a new player is added to the tracker is just easier to do, so that is what this patch does. Fixes https://github.com/PaperMC/Folia/issues/197 --- ...er-desync-when-new-players-are-added.patch | 85 +++++++++++++++++++ 1 file changed, 85 insertions(+) create mode 100644 patches/server/0019-Fix-entity-tracker-desync-when-new-players-are-added.patch diff --git a/patches/server/0019-Fix-entity-tracker-desync-when-new-players-are-added.patch b/patches/server/0019-Fix-entity-tracker-desync-when-new-players-are-added.patch new file mode 100644 index 0000000..8d75f69 --- /dev/null +++ b/patches/server/0019-Fix-entity-tracker-desync-when-new-players-are-added.patch @@ -0,0 +1,85 @@ +From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 +From: Spottedleaf +Date: Tue, 20 Feb 2024 18:24:16 -0800 +Subject: [PATCH] Fix entity tracker desync when new players are added to the + tracker + +The delta position packet instructs the client to update +the entity position by a position difference. However, this position +difference is relative to the last position in the entity tracker +state, not the last position which has been sent to the player. As +a result, if the last position the player has recorded is different +than the one stored in the entity tracker (which occurs when a new +player is added to an existing entity tracker state) then the sent +position difference will cause a position desync for the client. + +We can resolve this problem by either tracking the last position +sent per-player, or by simply resetting the last sent position +in the entity tracker state every time a new player is added. +Resetting the last sent position every time a new player is +added to the tracker is just easier to do, so that is what +this patch does. + +diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java +index 21ec49acb3c1241d9286959c42a7f8363f637e4f..79e507c1463dbb9039b1fed8bdf41c0ee5f4fec3 100644 +--- a/src/main/java/net/minecraft/server/level/ChunkMap.java ++++ b/src/main/java/net/minecraft/server/level/ChunkMap.java +@@ -1419,6 +1419,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider + this.serverEntity.addPairing(player); + } + // Paper end - entity tracking events ++ this.serverEntity.onPlayerAdd(); // Paper - fix desync when a player is added to the tracker + } + } else if (this.seenBy.remove(player.connection)) { + this.serverEntity.removePairing(player); +diff --git a/src/main/java/net/minecraft/server/level/ServerEntity.java b/src/main/java/net/minecraft/server/level/ServerEntity.java +index 529ab44baaf573b97cf7e89560c548642733188f..16373e0c5ea38199fab3eb289bf2a5fcf0dd7439 100644 +--- a/src/main/java/net/minecraft/server/level/ServerEntity.java ++++ b/src/main/java/net/minecraft/server/level/ServerEntity.java +@@ -93,6 +93,13 @@ public class ServerEntity { + this.trackedDataValues = entity.getEntityData().getNonDefaultValues(); + } + ++ // Paper start - fix desync when a player is added to the tracker ++ private boolean forceStateResync; ++ public void onPlayerAdd() { ++ this.forceStateResync = true; ++ } ++ // Paper end - fix desync when a player is added to the tracker ++ + public void sendChanges() { + List list = this.entity.getPassengers(); + +@@ -141,7 +148,7 @@ public class ServerEntity { + } + } + +- if (this.tickCount % this.updateInterval == 0 || this.entity.hasImpulse || this.entity.getEntityData().isDirty()) { ++ if (this.forceStateResync || this.tickCount % this.updateInterval == 0 || this.entity.hasImpulse || this.entity.getEntityData().isDirty()) { // Paper - fix desync when a player is added to the tracker + int i; + int j; + +@@ -177,13 +184,13 @@ public class ServerEntity { + boolean flag4 = false; + boolean flag5 = false; + +- if (!(this.entity instanceof net.minecraft.world.entity.decoration.HangingEntity) || this.tickCount > 0 || this.entity instanceof AbstractArrow) { // Paper - Always update position to fix first-tick teleports ++ if (this.forceStateResync || !(this.entity instanceof net.minecraft.world.entity.decoration.HangingEntity) || this.tickCount > 0 || this.entity instanceof AbstractArrow) { // Paper - Always update position to fix first-tick teleports + long k = this.positionCodec.encodeX(vec3d); + long l = this.positionCodec.encodeY(vec3d); + long i1 = this.positionCodec.encodeZ(vec3d); + boolean flag6 = k < -32768L || k > 32767L || l < -32768L || l > 32767L || i1 < -32768L || i1 > 32767L; + +- if (!flag6 && this.teleportDelay <= 400 && !this.wasRiding && this.wasOnGround == this.entity.onGround()&& !(io.papermc.paper.configuration.GlobalConfiguration.get().collisions.sendFullPosForHardCollidingEntities && this.entity.hardCollides())) { // Paper - send full pos for hard colliding entities to prevent collision problems due to desync ++ if (!this.forceStateResync && !flag6 && this.teleportDelay <= 400 && !this.wasRiding && this.wasOnGround == this.entity.onGround()&& !(io.papermc.paper.configuration.GlobalConfiguration.get().collisions.sendFullPosForHardCollidingEntities && this.entity.hardCollides())) { // Paper - send full pos for hard colliding entities to prevent collision problems due to desync + if ((!flag2 || !flag3) && !(this.entity instanceof AbstractArrow)) { + if (flag2) { + packet1 = new ClientboundMoveEntityPacket.Pos(this.entity.getId(), (short) ((int) k), (short) ((int) l), (short) ((int) i1), this.entity.onGround()); +@@ -240,6 +247,7 @@ public class ServerEntity { + } + + this.entity.hasImpulse = false; ++ this.forceStateResync = false; // Paper - fix desync when a player is added to the tracker + } + + ++this.tickCount;