PaperMC/paper-server/patches/sources/net/minecraft/world/level/ServerExplosion.java.patch

--- a/net/minecraft/world/level/ServerExplosion.java
+++ b/net/minecraft/world/level/ServerExplosion.java
@@ -22,18 +22,27 @@
 import net.minecraft.world.entity.EntityType;
 import net.minecraft.world.entity.LivingEntity;
 import net.minecraft.world.entity.ai.attributes.Attributes;
+import net.minecraft.world.entity.boss.EnderDragonPart;
+import net.minecraft.world.entity.boss.enderdragon.EnderDragon;
 import net.minecraft.world.entity.item.ItemEntity;
 import net.minecraft.world.entity.item.PrimedTnt;
 import net.minecraft.world.entity.player.Player;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.level.block.BaseFireBlock;
 import net.minecraft.world.level.block.Block;
-import net.minecraft.world.level.block.state.BlockState;
 import net.minecraft.world.level.gameevent.GameEvent;
 import net.minecraft.world.level.material.FluidState;
 import net.minecraft.world.phys.AABB;
 import net.minecraft.world.phys.HitResult;
 import net.minecraft.world.phys.Vec3;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.state.BlockState;
+import org.bukkit.craftbukkit.event.CraftEventFactory;
+import org.bukkit.craftbukkit.util.CraftLocation;
+import org.bukkit.event.entity.EntityExplodeEvent;
+import org.bukkit.Location;
+import org.bukkit.event.block.BlockExplodeEvent;
+// CraftBukkit end
 
 public class ServerExplosion implements Explosion {
 
@@ -50,16 +59,22 @@
     private final DamageSource damageSource;
     private final ExplosionDamageCalculator damageCalculator;
     private final Map<Player, Vec3> hitPlayers = new HashMap();
+    // CraftBukkit - add field
+    public boolean wasCanceled = false;
+    public float yield;
+    // CraftBukkit end
+    public boolean excludeSourceFromDamage = true; // Paper - Allow explosions to damage source
 
     public ServerExplosion(ServerLevel world, @Nullable Entity entity, @Nullable DamageSource damageSource, @Nullable ExplosionDamageCalculator behavior, Vec3 pos, float power, boolean createFire, Explosion.BlockInteraction destructionType) {
         this.level = world;
         this.source = entity;
-        this.radius = power;
+        this.radius = (float) Math.max(power, 0.0); // CraftBukkit - clamp bad values
         this.center = pos;
         this.fire = createFire;
         this.blockInteraction = destructionType;
         this.damageSource = damageSource == null ? world.damageSources().explosion(this) : damageSource;
         this.damageCalculator = behavior == null ? this.makeDamageCalculator(entity) : behavior;
+        this.yield = this.blockInteraction == Explosion.BlockInteraction.DESTROY_WITH_DECAY ? 1.0F / this.radius : 1.0F; // CraftBukkit
     }
 
     private ExplosionDamageCalculator makeDamageCalculator(@Nullable Entity entity) {
@@ -135,7 +150,7 @@
                         for (float f1 = 0.3F; f > 0.0F; f -= 0.22500001F) {
                             BlockPos blockposition = BlockPos.containing(d4, d5, d6);
                             BlockState iblockdata = this.level.getBlockState(blockposition);
-                            FluidState fluid = this.level.getFluidState(blockposition);
+                            FluidState fluid = iblockdata.getFluidState(); // Paper - Perf: Optimize call to getFluid for explosions
 
                             if (!this.level.isInWorldBounds(blockposition)) {
                                 break;
@@ -149,6 +164,15 @@
 
                             if (f > 0.0F && this.damageCalculator.shouldBlockExplode(this, this.level, blockposition, iblockdata, f)) {
                                 set.add(blockposition);
+                                // Paper start - prevent headless pistons from forming
+                                if (!io.papermc.paper.configuration.GlobalConfiguration.get().unsupportedSettings.allowHeadlessPistons && iblockdata.getBlock() == Blocks.MOVING_PISTON) {
+                                    net.minecraft.world.level.block.entity.BlockEntity extension = this.level.getBlockEntity(blockposition);
+                                    if (extension instanceof net.minecraft.world.level.block.piston.PistonMovingBlockEntity blockEntity && blockEntity.isSourcePiston()) {
+                                        net.minecraft.core.Direction direction = iblockdata.getValue(net.minecraft.world.level.block.piston.PistonHeadBlock.FACING);
+                                        set.add(blockposition.relative(direction.getOpposite()));
+                                    }
+                                }
+                                // Paper end - prevent headless pistons from forming
                             }
 
                             d4 += d0 * 0.30000001192092896D;
@@ -171,7 +195,7 @@
         int l = Mth.floor(this.center.y + (double) f + 1.0D);
         int i1 = Mth.floor(this.center.z - (double) f - 1.0D);
         int j1 = Mth.floor(this.center.z + (double) f + 1.0D);
-        List<Entity> list = this.level.getEntities(this.source, new AABB((double) i, (double) k, (double) i1, (double) j, (double) l, (double) j1));
+        List<Entity> list = this.level.getEntities(excludeSourceFromDamage ? this.source : null, new AABB((double) i, (double) k, (double) i1, (double) j, (double) l, (double) j1), (com.google.common.base.Predicate<Entity>) entity -> entity.isAlive() && !entity.isSpectator()); // Paper - Fix lag from explosions processing dead entities, Allow explosions to damage source
         Iterator iterator = list.iterator();
 
         while (iterator.hasNext()) {
@@ -192,10 +216,38 @@
                         d3 /= d4;
                         boolean flag = this.damageCalculator.shouldDamageEntity(this, entity);
                         float f1 = this.damageCalculator.getKnockbackMultiplier(entity);
-                        float f2 = !flag && f1 == 0.0F ? 0.0F : ServerExplosion.getSeenPercent(this.center, entity);
+                        float f2 = !flag && f1 == 0.0F ? 0.0F : this.getBlockDensity(this.center, entity); // Paper - Optimize explosions
 
                         if (flag) {
-                            entity.hurtServer(this.level, this.damageSource, this.damageCalculator.getEntityDamageAmount(this, entity, f2));
+                            // CraftBukkit start
+
+                            // Special case ender dragon only give knockback if no damage is cancelled
+                            // Thinks to note:
+                            // - Setting a velocity to a ComplexEntityPart is ignored (and therefore not needed)
+                            // - Damaging ComplexEntityPart while forward the damage to EntityEnderDragon
+                            // - Damaging EntityEnderDragon does nothing
+                            // - EntityEnderDragon hitbock always covers the other parts and is therefore always present
+                            if (entity instanceof EnderDragonPart) {
+                                continue;
+                            }
+
+                            entity.lastDamageCancelled = false;
+
+                            if (entity instanceof EnderDragon) {
+                                for (EnderDragonPart entityComplexPart : ((EnderDragon) entity).subEntities) {
+                                    // Calculate damage separately for each EntityComplexPart
+                                    if (list.contains(entityComplexPart)) {
+                                        entityComplexPart.hurtServer(this.level, this.damageSource, this.damageCalculator.getEntityDamageAmount(this, entity, f2));
+                                    }
+                                }
+                            } else {
+                                entity.hurtServer(this.level, this.damageSource, this.damageCalculator.getEntityDamageAmount(this, entity, f2));
+                            }
+
+                            if (entity.lastDamageCancelled) { // SPIGOT-5339, SPIGOT-6252, SPIGOT-6777: Skip entity if damage event was cancelled
+                                continue;
+                            }
+                            // CraftBukkit end
                         }
 
                         double d5 = (1.0D - d0) * (double) f2 * (double) f1;
@@ -204,7 +256,7 @@
                         if (entity instanceof LivingEntity) {
                             LivingEntity entityliving = (LivingEntity) entity;
 
-                            d6 = d5 * (1.0D - entityliving.getAttributeValue(Attributes.EXPLOSION_KNOCKBACK_RESISTANCE));
+                            d6 = entity instanceof Player && this.level.paperConfig().environment.disableExplosionKnockback ? 0 : d5 * (1.0D - entityliving.getAttributeValue(Attributes.EXPLOSION_KNOCKBACK_RESISTANCE)); // Paper
                         } else {
                             d6 = d5;
                         }
@@ -214,11 +266,19 @@
                         d3 *= d6;
                         Vec3 vec3d = new Vec3(d1, d2, d3);
 
+                        // CraftBukkit start - Call EntityKnockbackEvent
+                        if (entity instanceof LivingEntity) {
+                           // Paper start - knockback events
+                           io.papermc.paper.event.entity.EntityKnockbackEvent event = CraftEventFactory.callEntityKnockbackEvent((org.bukkit.craftbukkit.entity.CraftLivingEntity) entity.getBukkitEntity(), this.source, this.damageSource.getEntity() != null ? this.damageSource.getEntity() : this.source, io.papermc.paper.event.entity.EntityKnockbackEvent.Cause.EXPLOSION, d6, vec3d);
+                            vec3d = event.isCancelled() ? Vec3.ZERO : org.bukkit.craftbukkit.util.CraftVector.toNMS(event.getKnockback());
+                           // Paper end - knockback events
+                        }
+                        // CraftBukkit end
                         entity.push(vec3d);
                         if (entity instanceof Player) {
                             Player entityhuman = (Player) entity;
 
-                            if (!entityhuman.isSpectator() && (!entityhuman.isCreative() || !entityhuman.getAbilities().flying)) {
+                            if (!entityhuman.isSpectator() && (!entityhuman.isCreative() || !entityhuman.getAbilities().flying) && !level.paperConfig().environment.disableExplosionKnockback) { // Paper - Option to disable explosion knockback
                                 this.hitPlayers.put(entityhuman, vec3d);
                             }
                         }
@@ -235,10 +295,62 @@
         List<ServerExplosion.StackCollector> list1 = new ArrayList();
 
         Util.shuffle(positions, this.level.random);
+        // CraftBukkit start
+        org.bukkit.World bworld = this.level.getWorld();
+        Location location = CraftLocation.toBukkit(this.center, bworld);
+
+        List<org.bukkit.block.Block> blockList = new ObjectArrayList<>();
+        for (int i1 = positions.size() - 1; i1 >= 0; i1--) {
+            BlockPos cpos = positions.get(i1);
+            org.bukkit.block.Block bblock = bworld.getBlockAt(cpos.getX(), cpos.getY(), cpos.getZ());
+            if (!bblock.getType().isAir()) {
+                blockList.add(bblock);
+            }
+        }
+
+        List<org.bukkit.block.Block> bukkitBlocks;
+
+        if (this.source != null) {
+            EntityExplodeEvent event = CraftEventFactory.callEntityExplodeEvent(this.source, blockList, this.yield, this.getBlockInteraction());
+            this.wasCanceled = event.isCancelled();
+            bukkitBlocks = event.blockList();
+            this.yield = event.getYield();
+        } else {
+            org.bukkit.block.Block block = location.getBlock();
+            org.bukkit.block.BlockState blockState = (this.damageSource.getDirectBlockState() != null) ? this.damageSource.getDirectBlockState() : block.getState();
+            BlockExplodeEvent event = CraftEventFactory.callBlockExplodeEvent(block, blockState, blockList, this.yield, this.getBlockInteraction());
+            this.wasCanceled = event.isCancelled();
+            bukkitBlocks = event.blockList();
+            this.yield = event.getYield();
+        }
+
+        positions.clear();
+
+        for (org.bukkit.block.Block bblock : bukkitBlocks) {
+            BlockPos coords = new BlockPos(bblock.getX(), bblock.getY(), bblock.getZ());
+            positions.add(coords);
+        }
+
+        if (this.wasCanceled) {
+            return;
+        }
+        // CraftBukkit end
         Iterator iterator = positions.iterator();
 
         while (iterator.hasNext()) {
             BlockPos blockposition = (BlockPos) iterator.next();
+            // CraftBukkit start - TNTPrimeEvent
+            BlockState iblockdata = this.level.getBlockState(blockposition);
+            Block block = iblockdata.getBlock();
+            if (block instanceof net.minecraft.world.level.block.TntBlock) {
+                Entity sourceEntity = this.source == null ? null : this.source;
+                BlockPos sourceBlock = sourceEntity == null ? BlockPos.containing(this.center) : null;
+                if (!CraftEventFactory.callTNTPrimeEvent(this.level, blockposition, org.bukkit.event.block.TNTPrimeEvent.PrimeCause.EXPLOSION, sourceEntity, sourceBlock)) {
+                    this.level.sendBlockUpdated(blockposition, Blocks.AIR.defaultBlockState(), iblockdata, 3); // Update the block on the client
+                    continue;
+                }
+            }
+            // CraftBukkit end
 
             this.level.getBlockState(blockposition).onExplosionHit(this.level, blockposition, this, (itemstack, blockposition1) -> {
                 ServerExplosion.addOrAppendStack(list1, itemstack, blockposition1);
@@ -262,13 +374,22 @@
             BlockPos blockposition = (BlockPos) iterator.next();
 
             if (this.level.random.nextInt(3) == 0 && this.level.getBlockState(blockposition).isAir() && this.level.getBlockState(blockposition.below()).isSolidRender()) {
-                this.level.setBlockAndUpdate(blockposition, BaseFireBlock.getState(this.level, blockposition));
+                // CraftBukkit start - Ignition by explosion
+                if (!org.bukkit.craftbukkit.event.CraftEventFactory.callBlockIgniteEvent(this.level, blockposition, this).isCancelled()) {
+                    this.level.setBlockAndUpdate(blockposition, BaseFireBlock.getState(this.level, blockposition));
+                }
+                // CraftBukkit end
             }
         }
 
     }
 
     public void explode() {
+        // CraftBukkit start
+        if (this.radius < 0.1F) {
+            return;
+        }
+        // CraftBukkit end
         this.level.gameEvent(this.source, (Holder) GameEvent.EXPLODE, this.center);
         List<BlockPos> list = this.calculateExplodedPositions();
 
@@ -288,6 +409,7 @@
     }
 
     private static void addOrAppendStack(List<ServerExplosion.StackCollector> droppedItemsOut, ItemStack item, BlockPos pos) {
+        if (item.isEmpty()) return; // CraftBukkit - SPIGOT-5425
         Iterator iterator = droppedItemsOut.iterator();
 
         do {
@@ -372,4 +494,85 @@
 
         }
     }
+
+    // Paper start - Optimize explosions
+    private float getBlockDensity(Vec3 vec3d, Entity entity) {
+        if (!this.level.paperConfig().environment.optimizeExplosions) {
+            return getSeenPercent(vec3d, entity);
+        }
+        CacheKey key = new CacheKey(this, entity.getBoundingBox());
+        Float blockDensity = this.level.explosionDensityCache.get(key);
+        if (blockDensity == null) {
+            blockDensity = getSeenPercent(vec3d, entity);
+            this.level.explosionDensityCache.put(key, blockDensity);
+        }
+
+        return blockDensity;
+    }
+
+    static class CacheKey {
+        private final Level world;
+        private final double posX, posY, posZ;
+        private final double minX, minY, minZ;
+        private final double maxX, maxY, maxZ;
+
+        public CacheKey(Explosion explosion, AABB aabb) {
+            this.world = explosion.level();
+            this.posX = explosion.center().x;
+            this.posY = explosion.center().y;
+            this.posZ = explosion.center().z;
+            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
 }