From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Wed, 15 Apr 2020 18:08:53 -0700
Subject: [PATCH] Optimise entity hard collision checking

Very few entities actually hard collide, so store them in their own
entity slices and provide a special getEntites type call just for them.
This reduces entity collision checking impact (in my testing) by 25%
for crammed entities (shove 130 cows into an 8x6 area in one chunk).
Less crammed entities are likely to show significantly less benefit.
Effectively, this patch optimises crammed entity situations.

diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
index 33456b0bb421d253aa8366210f41a9da7dcd1699..750fb07756f7e40b21f8ab0925f2e842aae50f7b 100644
--- a/src/main/java/net/minecraft/server/Chunk.java
+++ b/src/main/java/net/minecraft/server/Chunk.java
@@ -90,6 +90,54 @@ public class Chunk implements IChunkAccess {
     private final int[] inventoryEntityCounts = new int[16];
     // Paper end
 
+    // Paper start - optimise hard collision handling
+    final com.destroystokyo.paper.util.maplist.EntityList[] hardCollidingEntities = new com.destroystokyo.paper.util.maplist.EntityList[16];
+
+    {
+        for (int i = 0, len = this.hardCollidingEntities.length; i < len; ++i) {
+            this.hardCollidingEntities[i] = new com.destroystokyo.paper.util.maplist.EntityList();
+        }
+    }
+
+    public final void getHardCollidingEntities(@Nullable Entity entity, AxisAlignedBB axisalignedbb, List<Entity> into) {
+        // copied from getEntities
+        int min = MathHelper.floor((axisalignedbb.minY - 2.0D) / 16.0D);
+        int max = MathHelper.floor((axisalignedbb.maxY + 2.0D) / 16.0D);
+
+        min = MathHelper.clamp(min, 0, this.hardCollidingEntities.length - 1);
+        max = MathHelper.clamp(max, 0, this.hardCollidingEntities.length - 1);
+
+        for (int k = min; k <= max; ++k) {
+            com.destroystokyo.paper.util.maplist.EntityList entityList = this.hardCollidingEntities[k];
+            Entity[] entities = entityList.getRawData();
+
+            for (int i = 0, len = entityList.size(); i < len; ++i) {
+                Entity entity1 = entities[i];
+                if (entity1.shouldBeRemoved) continue; // Paper
+
+                if (entity1 != entity && entity1.getBoundingBox().intersects(axisalignedbb)) {
+                    into.add(entity1);
+
+                    if (!(entity1 instanceof EntityEnderDragon)) {
+                        continue;
+                    }
+
+                    EntityComplexPart[] aentitycomplexpart = ((EntityEnderDragon) entity1).getComplexParts();
+                    int l = aentitycomplexpart.length;
+
+                    for (int i1 = 0; i1 < l; ++i1) {
+                        EntityComplexPart entitycomplexpart = aentitycomplexpart[i1];
+
+                        if (entitycomplexpart != entity && entitycomplexpart.getBoundingBox().intersects(axisalignedbb)) {
+                            into.add(entitycomplexpart);
+                        }
+                    }
+                }
+            }
+        }
+    }
+    // Paper end - optimise hard collision handling
+
     public Chunk(World world, ChunkCoordIntPair chunkcoordintpair, BiomeStorage biomestorage, ChunkConverter chunkconverter, TickList<Block> ticklist, TickList<FluidType> ticklist1, long i, @Nullable ChunkSection[] achunksection, @Nullable Consumer<Chunk> consumer) {
         this.sections = new ChunkSection[16];
         this.e = Maps.newHashMap();
@@ -539,7 +587,7 @@ public class Chunk implements IChunkAccess {
         entity.chunkY = k;
         entity.chunkZ = this.loc.z;
         this.entities.add(entity); // Paper - per chunk entity list
-        this.entitySlices[k].add(entity);
+        this.entitySlices[k].add(entity); if (entity.hardCollides()) this.hardCollidingEntities[k].add(entity); // Paper - optimise hard colliding entities
         // Paper start
         if (entity instanceof EntityItem) {
             itemCounts[k]++;
@@ -576,7 +624,7 @@ public class Chunk implements IChunkAccess {
             entity.entitySlice = null;
             entity.inChunk = false;
         }
-        if (!this.entitySlices[i].remove(entity)) {
+        if (entity.hardCollides()) this.hardCollidingEntities[i].remove(entity); if (!this.entitySlices[i].remove(entity)) { // Paper - optimise hard colliding entities
             return;
         }
         if (entity instanceof EntityItem) {
diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
index 7fb34a86dc35cb4bf51e1ce5220e56642096fece..f20f798f0f7bb765ffdab8672f4bf77a60fa52d2 100644
--- a/src/main/java/net/minecraft/server/Entity.java
+++ b/src/main/java/net/minecraft/server/Entity.java
@@ -211,6 +211,40 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
     }
     // CraftBukkit end
 
+    // Paper start
+    /**
+     * Overriding this field will cause memory leaks.
+     */
+    private final boolean hardCollides;
+
+    private static final java.util.Map<Class<? extends Entity>, Boolean> cachedOverrides = java.util.Collections.synchronizedMap(new java.util.WeakHashMap<>());
+    {
+        Boolean hardCollides = cachedOverrides.get(this.getClass());
+        if (hardCollides == null) {
+            try {
+                Object getHardCollisionBoxMethod = Entity.class.getMethod("au");
+                Object getHardCollisionBoxEntityMethod = Entity.class.getMethod("j", Entity.class);
+                if (!this.getClass().getMethod("au").equals(getHardCollisionBoxMethod)) {
+                    hardCollides = Boolean.TRUE;
+                } else if (!this.getClass().getMethod("j", Entity.class).equals(getHardCollisionBoxEntityMethod)) {
+                    hardCollides = Boolean.TRUE;
+                } else {
+                    hardCollides = Boolean.FALSE;
+                }
+                cachedOverrides.put(this.getClass(), hardCollides);
+            } catch (Throwable thr) {
+                // shouldn't happen, just explode
+                throw new RuntimeException(thr);
+            }
+        }
+        this.hardCollides = hardCollides.booleanValue();
+    }
+
+    public final boolean hardCollides() {
+        return this.hardCollides;
+    }
+    // Paper end
+
     public Entity(EntityTypes<?> entitytypes, World world) {
         this.id = Entity.entityCount.incrementAndGet();
         this.passengers = Lists.newArrayList();
diff --git a/src/main/java/net/minecraft/server/EntityEnderDragon.java b/src/main/java/net/minecraft/server/EntityEnderDragon.java
index 5bf99e0028b886a6ba1d2f39f8dc4cd3c9aa0943..aecdaacfc7da560759bc513680d76f55820d5046 100644
--- a/src/main/java/net/minecraft/server/EntityEnderDragon.java
+++ b/src/main/java/net/minecraft/server/EntityEnderDragon.java
@@ -847,6 +847,7 @@ public class EntityEnderDragon extends EntityInsentient implements IMonster {
     @Override
     public void checkDespawn() {}
 
+    public final EntityComplexPart[] getComplexParts() { return this.eo(); } // Paper - OBFHELPER
     public EntityComplexPart[] eo() {
         return this.children;
     }
diff --git a/src/main/java/net/minecraft/server/IEntityAccess.java b/src/main/java/net/minecraft/server/IEntityAccess.java
index 4157e50e4d99c029759bffcb48a8d645487554c8..5135308fb6137a34ed6fd061f0a210de6de4e81c 100644
--- a/src/main/java/net/minecraft/server/IEntityAccess.java
+++ b/src/main/java/net/minecraft/server/IEntityAccess.java
@@ -42,17 +42,26 @@ public interface IEntityAccess {
         return this.b(oclass, axisalignedbb, IEntitySelector.f);
     }
 
+    // Paper start - optimise hard collision
+    /**
+     * Not guaranteed to only return hard colliding entites
+     */
+    default List<Entity> getHardCollidingEntities(@Nullable Entity entity, AxisAlignedBB axisalignedbb) {
+        return this.getEntities(entity, axisalignedbb);
+    }
+    // Paper end - optimise hard collision
+
     default Stream<VoxelShape> b(@Nullable Entity entity, AxisAlignedBB axisalignedbb, Set<Entity> set) {
         if (axisalignedbb.a() < 1.0E-7D) {
             return Stream.empty();
         } else {
             AxisAlignedBB axisalignedbb1 = axisalignedbb.g(1.0E-7D);
-            Stream<AxisAlignedBB> stream = this.getEntities(entity, axisalignedbb1).stream().filter((entity1) -> { // Paper - decompile fix
+            Stream<AxisAlignedBB> stream = ((entity != null && entity.hardCollides()) ? this.getEntities(entity, axisalignedbb) : this.getHardCollidingEntities(entity, axisalignedbb1)).stream().filter((entity1) -> { // Paper - decompile fix // Paper - optimise hard collision
                 return !set.contains(entity1);
             }).filter((entity1) -> {
                 return entity == null || !entity.isSameVehicle(entity1);
             }).flatMap((entity1) -> {
-                return Stream.of(entity1.au(), entity == null ? null : entity.j(entity1));
+                return Stream.of(entity1.au(), entity == null ? null : entity.j(entity1)); // Paper - optimise hard collision - diff on change, these are the methods that only hard colliding entities override
             }).filter(Objects::nonNull);
 
             return stream.filter(axisalignedbb1::c).map(VoxelShapes::a);
diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
index c8619af2cf43041e3eebec74e24c7f127a662efe..899c535c4056cd2375ab8f834f03267d405f4bda 100644
--- a/src/main/java/net/minecraft/server/World.java
+++ b/src/main/java/net/minecraft/server/World.java
@@ -1178,6 +1178,32 @@ public abstract class World implements GeneratorAccess, AutoCloseable {
         return this.getChunkAt(i, j, ChunkStatus.FULL, false);
     }
 
+    // Paper start - optimise hard collision handling
+    @Override
+    public List<Entity> getHardCollidingEntities(@Nullable Entity entity, AxisAlignedBB axisalignedbb) {
+        // copied from below
+        List<Entity> list = Lists.newArrayList();
+        int i = MathHelper.floor((axisalignedbb.minX - 2.0D) / 16.0D);
+        int j = MathHelper.floor((axisalignedbb.maxX + 2.0D) / 16.0D);
+        int k = MathHelper.floor((axisalignedbb.minZ - 2.0D) / 16.0D);
+        int l = MathHelper.floor((axisalignedbb.maxZ + 2.0D) / 16.0D);
+
+        ChunkProviderServer chunkProvider = ((ChunkProviderServer)this.chunkProvider);
+
+        for (int i1 = i; i1 <= j; ++i1) {
+            for (int j1 = k; j1 <= l; ++j1) {
+                Chunk chunk = chunkProvider.getChunkAtIfLoadedMainThread(i1, j1);
+
+                if (chunk != null) {
+                    chunk.getHardCollidingEntities(entity, axisalignedbb, list);
+                }
+            }
+        }
+
+        return list;
+    }
+    // Paper end - optimise hard collision handling
+
     @Override
     public List<Entity> getEntities(@Nullable Entity entity, AxisAlignedBB axisalignedbb, @Nullable Predicate<? super Entity> predicate) {
         this.getMethodProfiler().c("getEntities");
