From bdafbcf48a32bfbede63ff359df1f1dfc81c23a5 Mon Sep 17 00:00:00 2001
From: Byteflux <byte@byteflux.net>
Date: Wed, 2 Mar 2016 11:59:48 -0600
Subject: [PATCH] Optimize explosions

The process of determining an entity's exposure from explosions can be
expensive when there are hundreds or more entities in range.

This patch adds a per-tick cache that is used for storing and retrieving
an entity's exposure during an explosion.

diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
index c2b9690a0c..a5ec0bc0e0 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -145,4 +145,10 @@ public class PaperWorldConfig {
         disableEndCredits = getBoolean("game-mechanics.disable-end-credits", false);
         log("End credits disabled: " + disableEndCredits);
     }
+
+    public boolean optimizeExplosions;
+    private void optimizeExplosions() {
+        optimizeExplosions = getBoolean("optimize-explosions", false);
+        log("Optimize explosions: " + optimizeExplosions);
+    }
 }
diff --git a/src/main/java/net/minecraft/server/Explosion.java b/src/main/java/net/minecraft/server/Explosion.java
index e1c628f177..bcff117619 100644
--- a/src/main/java/net/minecraft/server/Explosion.java
+++ b/src/main/java/net/minecraft/server/Explosion.java
@@ -172,7 +172,7 @@ public class Explosion {
                         d8 /= d11;
                         d9 /= d11;
                         d10 /= d11;
-                        double d12 = (double) a(vec3d, entity);
+                        double d12 = this.getBlockDensity(vec3d, entity); // Paper - Optimize explosions
                         double d13 = (1.0D - d7) * d12;
 
                         // CraftBukkit start
@@ -361,4 +361,84 @@ public class Explosion {
 
         private Effect() {}
     }
+    // Paper start - Optimize explosions
+    private float getBlockDensity(Vec3D vec3d, Entity entity) {
+        if (!this.world.paperConfig.optimizeExplosions) {
+            return a(vec3d, entity);
+        }
+        CacheKey key = new CacheKey(this, entity.getBoundingBox());
+        Float blockDensity = this.world.explosionDensityCache.get(key);
+        if (blockDensity == null) {
+            blockDensity = a(vec3d, entity);
+            this.world.explosionDensityCache.put(key, blockDensity);
+        }
+
+        return blockDensity;
+    }
+
+    static class CacheKey {
+        private final World world;
+        private final double posX, posY, posZ;
+        private final double minX, minY, minZ;
+        private final double maxX, maxY, maxZ;
+
+        public CacheKey(Explosion explosion, AxisAlignedBB aabb) {
+            this.world = explosion.world;
+            this.posX = explosion.posX;
+            this.posY = explosion.posY;
+            this.posZ = explosion.posZ;
+            this.minX = aabb.minX;
+            this.minY = aabb.minY;
+            this.minZ = aabb.minZ;
+            this.maxX = aabb.maxX;
+            this.maxY = aabb.maxY;
+            this.maxZ = aabb.maxZ;
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) return true;
+            if (o == null || getClass() != o.getClass()) return false;
+
+            CacheKey cacheKey = (CacheKey) o;
+
+            if (Double.compare(cacheKey.posX, posX) != 0) return false;
+            if (Double.compare(cacheKey.posY, posY) != 0) return false;
+            if (Double.compare(cacheKey.posZ, posZ) != 0) return false;
+            if (Double.compare(cacheKey.minX, minX) != 0) return false;
+            if (Double.compare(cacheKey.minY, minY) != 0) return false;
+            if (Double.compare(cacheKey.minZ, minZ) != 0) return false;
+            if (Double.compare(cacheKey.maxX, maxX) != 0) return false;
+            if (Double.compare(cacheKey.maxY, maxY) != 0) return false;
+            if (Double.compare(cacheKey.maxZ, maxZ) != 0) return false;
+            return world.equals(cacheKey.world);
+        }
+
+        @Override
+        public int hashCode() {
+            int result;
+            long temp;
+            result = world.hashCode();
+            temp = Double.doubleToLongBits(posX);
+            result = 31 * result + (int) (temp ^ (temp >>> 32));
+            temp = Double.doubleToLongBits(posY);
+            result = 31 * result + (int) (temp ^ (temp >>> 32));
+            temp = Double.doubleToLongBits(posZ);
+            result = 31 * result + (int) (temp ^ (temp >>> 32));
+            temp = Double.doubleToLongBits(minX);
+            result = 31 * result + (int) (temp ^ (temp >>> 32));
+            temp = Double.doubleToLongBits(minY);
+            result = 31 * result + (int) (temp ^ (temp >>> 32));
+            temp = Double.doubleToLongBits(minZ);
+            result = 31 * result + (int) (temp ^ (temp >>> 32));
+            temp = Double.doubleToLongBits(maxX);
+            result = 31 * result + (int) (temp ^ (temp >>> 32));
+            temp = Double.doubleToLongBits(maxY);
+            result = 31 * result + (int) (temp ^ (temp >>> 32));
+            temp = Double.doubleToLongBits(maxZ);
+            result = 31 * result + (int) (temp ^ (temp >>> 32));
+            return result;
+        }
+    }
+    // Paper end
 }
diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
index 7dfe1f0a3c..8704c091d7 100644
--- a/src/main/java/net/minecraft/server/MinecraftServer.java
+++ b/src/main/java/net/minecraft/server/MinecraftServer.java
@@ -1122,6 +1122,7 @@ public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTas
 
                 this.methodProfiler.exit();
                 this.methodProfiler.exit();
+                worldserver.explosionDensityCache.clear(); // Paper - Optimize explosions
             }
         }
 
diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
index 62c77d8f51..25f19091c7 100644
--- a/src/main/java/net/minecraft/server/World.java
+++ b/src/main/java/net/minecraft/server/World.java
@@ -19,6 +19,7 @@ import org.apache.logging.log4j.util.Supplier;
 // CraftBukkit start
 import com.google.common.collect.Maps;
 import java.util.ArrayList;
+import java.util.HashMap; // Paper
 import java.util.Map;
 import org.bukkit.Bukkit;
 import org.bukkit.block.BlockState;
@@ -94,6 +95,7 @@ public abstract class World implements IIBlockAccess, GeneratorAccess, AutoClose
     private org.spigotmc.TickLimiter entityLimiter;
     private org.spigotmc.TickLimiter tileLimiter;
     private int tileTickPosition;
+    public final Map<Explosion.CacheKey, Float> explosionDensityCache = new HashMap<>(); // Paper - Optimize explosions
 
     public CraftWorld getWorld() {
         return this.world;
-- 
2.21.0