PaperMC/patches/server-remapped/Workaround-for-Client-Lag-Spikes-MC-162253.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: MeFisto94 <MeFisto94@users.noreply.github.com>
Date: Tue, 12 May 2020 23:02:43 +0200
Subject: [PATCH] Workaround for Client Lag Spikes (MC-162253)

When crossing certain chunk boundaries, the client needlessly
calculates light maps for chunk neighbours. In some specific map
configurations, these calculations cause a 500ms+ freeze on the Client.

This patch basically serves as a workaround by sending light maps
to the client, so that it doesn't attempt to calculate them.
This mitigates the frametime impact to a minimum (but it's still there).

diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
@@ -0,0 +0,0 @@ import net.minecraft.world.level.chunk.ChunkGenerator;
 import net.minecraft.world.level.chunk.ChunkStatus;
 import net.minecraft.world.level.chunk.ImposterProtoChunk;
 import net.minecraft.world.level.chunk.LevelChunk;
+import net.minecraft.world.level.chunk.LevelChunkSection;
 import net.minecraft.world.level.chunk.LightChunkGetter;
 import net.minecraft.world.level.chunk.ProtoChunk;
 import net.minecraft.world.level.chunk.UpgradeData;
@@ -0,0 +0,0 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
 
     // Paper start
     private static int getLightMask(final LevelChunk chunk) {
-        final ChunkSection[] chunkSections = chunk.getSections();
+        final LevelChunkSection[] chunkSections = chunk.getSections();
         int mask = 0;
 
         for (int i = 0; i < chunkSections.length; ++i) {
@@ -0,0 +0,0 @@ Lightmasks have 18 bits, from the -1 (void) section until the 17th (air) section
 Sections go from 0..16. Now whenever a section is not empty, it can potentially change lighting for the section itself, the section below and the section above, hence the bitmask 111b, which is 7d.
 
              */
-            mask |= (ChunkSection.isEmpty(chunkSections[i]) ? 0 : 7) << i;
+            mask |= (LevelChunkSection.isEmpty(chunkSections[i]) ? 0 : 7) << i;
         }
 
         return mask;
@@ -0,0 +0,0 @@ Sections go from 0..16. Now whenever a section is not empty, it can potentially
     public final void sendChunk(ServerPlayer entityplayer, Packet<?>[] apacket, LevelChunk chunk) { this.playerLoadedChunk(entityplayer, apacket, chunk); } // Paper - OBFHELPER
     private void playerLoadedChunk(ServerPlayer player, Packet<?>[] packets, LevelChunk chunk) {
         if (packets[0] == null) {
+            // Paper start - add 8 for light fix workaround
+            if (packets.length != 10) { // in case Plugins call sendChunk, resize
+                packets = new Packet[10];
+            }
+            // Paper end
             packets[0] = new ClientboundLevelChunkPacket(chunk, 65535, chunk.world.chunkPacketBlockController.shouldModify(player, chunk, 65535)); // Paper - Anti-Xray - Bypass
             packets[1] = new ClientboundLightUpdatePacket(chunk.getPos(), this.lightEngine, true);
+
+            // Paper start - Fix MC-162253
+            final int lightMask = getLightMask(chunk);
+            int i = 1;
+            for (int x = -1; x <= 1; x++) {
+                for (int z = -1; z <= 1; z++) {
+                    if (x == 0 && z == 0) {
+                        continue;
+                    }
+
+                    ++i;
+
+                    if (!chunk.isNeighbourLoaded(x, z)) {
+                        continue;
+                    }
+
+                    final LevelChunk neighbor = chunk.getRelativeNeighbourIfLoaded(x, z);
+                    final int updateLightMask = lightMask & ~getCeilingLightMask(neighbor);
+
+                    if (updateLightMask == 0) {
+                        continue;
+                    }
+
+                    packets[i] = new ClientboundLightUpdatePacket(new ChunkPos(chunk.getPos().x + x, chunk.getPos().z + z), lightEngine, updateLightMask, 0, true);
+                }
+            }
+        }
+
+        final int viewDistance = playerViewDistanceBroadcastMap.getLastViewDistance(player);
+        final long lastPosition = playerViewDistanceBroadcastMap.getLastCoordinate(player);
+
+        int j = 1;
+        for (int x = -1; x <= 1; x++) {
+            for (int z = -1; z <= 1; z++) {
+                if (x == 0 && z == 0) {
+                    continue;
+                }
+
+                ++j;
+
+                Packet<?> packet = packets[j];
+                if (packet == null) {
+                    continue;
+                }
+
+                final int distX = Math.abs(MCUtil.getCoordinateX(lastPosition) - (chunk.getPos().x + x));
+                final int distZ = Math.abs(MCUtil.getCoordinateZ(lastPosition) - (chunk.getPos().z + z));
+
+                if (Math.max(distX, distZ) > viewDistance) {
+                    continue;
+                }
+                player.connection.send(packet);
+            }
         }
+        // Paper end - Fix MC-162253
 
         player.trackChunk(chunk.getPos(), packets[0], packets[1]);
         DebugPackets.sendPoiPacketsForChunk(this.level, chunk.getPos());
diff --git a/src/main/java/net/minecraft/world/level/chunk/LevelChunk.java b/src/main/java/net/minecraft/world/level/chunk/LevelChunk.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/world/level/chunk/LevelChunk.java
+++ b/src/main/java/net/minecraft/world/level/chunk/LevelChunk.java
@@ -0,0 +0,0 @@ public class LevelChunk implements ChunkAccess {
 
                     // broadcast
                     Object[] backingSet = inRange.getBackingSet();
-                    Packet[] chunkPackets = new Packet[2];
+                    Packet[] chunkPackets = new Packet[10];
                     for (int index = 0, len = backingSet.length; index < len; ++index) {
                         Object temp = backingSet[index];
                         if (!(temp instanceof ServerPlayer)) {
diff --git a/src/main/java/net/minecraft/world/level/chunk/LevelChunkSection.java b/src/main/java/net/minecraft/world/level/chunk/LevelChunkSection.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/world/level/chunk/LevelChunkSection.java
+++ b/src/main/java/net/minecraft/world/level/chunk/LevelChunkSection.java
@@ -0,0 +0,0 @@ public class LevelChunkSection {
         return this.nonEmptyBlockCount == 0;
     }
 
+    public static boolean isEmpty(@Nullable LevelChunkSection chunksection) { return isEmpty(chunksection) ; } // Paper - OBFHELPER
     public static boolean isEmpty(@Nullable LevelChunkSection section) {
         return section == LevelChunk.EMPTY_SECTION || section.isEmpty();
     }