Paper/patches/unapplied/server/1020-Actually-optimise-explosions.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Tue, 12 Sep 2023 06:50:16 -0700
Subject: [PATCH] Actually optimise explosions

The vast majority of blocks an explosion of power ~4 tries
to destroy are duplicates. The core of the block destroying
part of this patch is to cache the block state, resistance, and
whether it should explode - as those will not change.

The other part of this patch is to optimise the visibility
percentage calculation. The new visibility calculation takes
advantage of the block caching already done by the explosion logic.
It continues to update the cache as the visibility calculation
uses many rays which can overlap significantly.

Effectively, the patch uses a lot of caching to eliminate
redundant operations.

Performance benchmarking explosions is challenging, as it varies
depending on the power, the number of nearby entities, and the
nearby terrain. This means that no benchmark can cover all the cases.
I decided to test a giant block of TNT, as that's where the optimisations
would be needed the most.

I tested using a 50x10x50 block of TNT above ground
and determined the following:

Vanilla time per explosion: 2.27ms
Lithium time per explosion: 1.07ms
This patch time per explosion: 0.45ms

The results indicate that this logic is 5 times faster than Vanilla
and 2.3 times faster than Lithium.

diff --git a/src/main/java/net/minecraft/world/level/Explosion.java b/src/main/java/net/minecraft/world/level/Explosion.java
index c1eafcc5b0e6486a6bffc497091e1d48b6b31a7e..45243249a561440512ef2a620c60b02e159c80e2 100644
--- a/src/main/java/net/minecraft/world/level/Explosion.java
+++ b/src/main/java/net/minecraft/world/level/Explosion.java
@@ -97,6 +97,271 @@ public class Explosion {
         this.damageCalculator = behavior == null ? this.makeDamageCalculator(entity) : behavior;
     }
 
+    // Paper start - optimise collisions
+    private static final double[] CACHED_RAYS;
+    static {
+        final it.unimi.dsi.fastutil.doubles.DoubleArrayList rayCoords = new it.unimi.dsi.fastutil.doubles.DoubleArrayList();
+
+        for (int x = 0; x <= 15; ++x) {
+            for (int y = 0; y <= 15; ++y) {
+                for (int z = 0; z <= 15; ++z) {
+                    if ((x == 0 || x == 15) || (y == 0 || y == 15) || (z == 0 || z == 15)) {
+                        double xDir = (double)((float)x / 15.0F * 2.0F - 1.0F);
+                        double yDir = (double)((float)y / 15.0F * 2.0F - 1.0F);
+                        double zDir = (double)((float)z / 15.0F * 2.0F - 1.0F);
+
+                        double mag = Math.sqrt(
+                                xDir * xDir + yDir * yDir + zDir * zDir
+                        );
+
+                        rayCoords.add((xDir / mag) * (double)0.3F);
+                        rayCoords.add((yDir / mag) * (double)0.3F);
+                        rayCoords.add((zDir / mag) * (double)0.3F);
+                    }
+                }
+            }
+        }
+
+        CACHED_RAYS = rayCoords.toDoubleArray();
+    }
+
+    private static final int CHUNK_CACHE_SHIFT = 2;
+    private static final int CHUNK_CACHE_MASK = (1 << CHUNK_CACHE_SHIFT) - 1;
+    private static final int CHUNK_CACHE_WIDTH = 1 << CHUNK_CACHE_SHIFT;
+
+    private static final int BLOCK_EXPLOSION_CACHE_SHIFT = 3;
+    private static final int BLOCK_EXPLOSION_CACHE_MASK = (1 << BLOCK_EXPLOSION_CACHE_SHIFT) - 1;
+    private static final int BLOCK_EXPLOSION_CACHE_WIDTH = 1 << BLOCK_EXPLOSION_CACHE_SHIFT;
+
+    // resistance = (res + 0.3F) * 0.3F;
+    // so for resistance = 0, we need res = -0.3F
+    private static final Float ZERO_RESISTANCE = Float.valueOf(-0.3f);
+    private it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap<ExplosionBlockCache> blockCache = null;
+
+    public static final class ExplosionBlockCache {
+
+        public final long key;
+        public final BlockPos immutablePos;
+        public final BlockState blockState;
+        public final FluidState fluidState;
+        public final float resistance;
+        public final boolean outOfWorld;
+        public Boolean shouldExplode; // null -> not called yet
+        public net.minecraft.world.phys.shapes.VoxelShape cachedCollisionShape;
+
+        public ExplosionBlockCache(long key, BlockPos immutablePos, BlockState blockState, FluidState fluidState, float resistance,
+                                   boolean outOfWorld) {
+            this.key = key;
+            this.immutablePos = immutablePos;
+            this.blockState = blockState;
+            this.fluidState = fluidState;
+            this.resistance = resistance;
+            this.outOfWorld = outOfWorld;
+        }
+    }
+
+    private long[] chunkPosCache = null;
+    private net.minecraft.world.level.chunk.LevelChunk[] chunkCache = null;
+
+    private ExplosionBlockCache getOrCacheExplosionBlock(final int x, final int y, final int z,
+                                                         final long key, final boolean calculateResistance) {
+        ExplosionBlockCache ret = this.blockCache.get(key);
+        if (ret != null) {
+            return ret;
+        }
+
+        BlockPos pos = new BlockPos(x, y, z);
+
+        if (!this.level.isInWorldBounds(pos)) {
+            ret = new ExplosionBlockCache(key, pos, null, null, 0.0f, true);
+        } else {
+            net.minecraft.world.level.chunk.LevelChunk chunk;
+            long chunkKey = io.papermc.paper.util.CoordinateUtils.getChunkKey(x >> 4, z >> 4);
+            int chunkCacheKey = ((x >> 4) & CHUNK_CACHE_MASK) | (((z >> 4) << CHUNK_CACHE_SHIFT) & (CHUNK_CACHE_MASK << CHUNK_CACHE_SHIFT));
+            if (this.chunkPosCache[chunkCacheKey] == chunkKey) {
+                chunk = this.chunkCache[chunkCacheKey];
+            } else {
+                this.chunkPosCache[chunkCacheKey] = chunkKey;
+                this.chunkCache[chunkCacheKey] = chunk = this.level.getChunk(x >> 4, z >> 4);
+            }
+
+            BlockState blockState = chunk.getBlockStateFinal(x, y, z);
+            FluidState fluidState = blockState.getFluidState();
+
+            Optional<Float> resistance = !calculateResistance ? Optional.empty() : this.damageCalculator.getBlockExplosionResistance((Explosion)(Object)this, this.level, pos, blockState, fluidState);
+
+            ret = new ExplosionBlockCache(
+                    key, pos, blockState, fluidState,
+                    (resistance.orElse(ZERO_RESISTANCE).floatValue() + 0.3f) * 0.3f,
+                    false
+            );
+        }
+
+        this.blockCache.put(key, ret);
+
+        return ret;
+    }
+
+    private boolean clipsAnything(final Vec3 from, final Vec3 to,
+                                  final io.papermc.paper.util.CollisionUtil.LazyEntityCollisionContext context,
+                                  final ExplosionBlockCache[] blockCache,
+                                  final BlockPos.MutableBlockPos currPos) {
+        // assume that context.delegated = false
+        final double adjX = io.papermc.paper.util.CollisionUtil.COLLISION_EPSILON * (from.x - to.x);
+        final double adjY = io.papermc.paper.util.CollisionUtil.COLLISION_EPSILON * (from.y - to.y);
+        final double adjZ = io.papermc.paper.util.CollisionUtil.COLLISION_EPSILON * (from.z - to.z);
+
+        if (adjX == 0.0 && adjY == 0.0 && adjZ == 0.0) {
+            return false;
+        }
+
+        final double toXAdj = to.x - adjX;
+        final double toYAdj = to.y - adjY;
+        final double toZAdj = to.z - adjZ;
+        final double fromXAdj = from.x + adjX;
+        final double fromYAdj = from.y + adjY;
+        final double fromZAdj = from.z + adjZ;
+
+        int currX = Mth.floor(fromXAdj);
+        int currY = Mth.floor(fromYAdj);
+        int currZ = Mth.floor(fromZAdj);
+
+        final double diffX = toXAdj - fromXAdj;
+        final double diffY = toYAdj - fromYAdj;
+        final double diffZ = toZAdj - fromZAdj;
+
+        final double dxDouble = Math.signum(diffX);
+        final double dyDouble = Math.signum(diffY);
+        final double dzDouble = Math.signum(diffZ);
+
+        final int dx = (int)dxDouble;
+        final int dy = (int)dyDouble;
+        final int dz = (int)dzDouble;
+
+        final double normalizedDiffX = diffX == 0.0 ? Double.MAX_VALUE : dxDouble / diffX;
+        final double normalizedDiffY = diffY == 0.0 ? Double.MAX_VALUE : dyDouble / diffY;
+        final double normalizedDiffZ = diffZ == 0.0 ? Double.MAX_VALUE : dzDouble / diffZ;
+
+        double normalizedCurrX = normalizedDiffX * (diffX > 0.0 ? (1.0 - Mth.frac(fromXAdj)) : Mth.frac(fromXAdj));
+        double normalizedCurrY = normalizedDiffY * (diffY > 0.0 ? (1.0 - Mth.frac(fromYAdj)) : Mth.frac(fromYAdj));
+        double normalizedCurrZ = normalizedDiffZ * (diffZ > 0.0 ? (1.0 - Mth.frac(fromZAdj)) : Mth.frac(fromZAdj));
+
+        for (;;) {
+            currPos.set(currX, currY, currZ);
+
+            // ClipContext.Block.COLLIDER -> BlockBehaviour.BlockStateBase::getCollisionShape
+            // ClipContext.Fluid.NONE -> ignore fluids
+
+            // read block from cache
+            final long key = BlockPos.asLong(currX, currY, currZ);
+
+            final int cacheKey =
+                    (currX & BLOCK_EXPLOSION_CACHE_MASK) |
+                    (currY & BLOCK_EXPLOSION_CACHE_MASK) << (BLOCK_EXPLOSION_CACHE_SHIFT) |
+                    (currZ & BLOCK_EXPLOSION_CACHE_MASK) << (BLOCK_EXPLOSION_CACHE_SHIFT + BLOCK_EXPLOSION_CACHE_SHIFT);
+            ExplosionBlockCache cachedBlock = blockCache[cacheKey];
+            if (cachedBlock == null || cachedBlock.key != key) {
+                blockCache[cacheKey] = cachedBlock = this.getOrCacheExplosionBlock(currX, currY, currZ, key, false);
+            }
+
+            final BlockState blockState = cachedBlock.blockState;
+            if (blockState != null && !blockState.emptyCollisionShape()) {
+                net.minecraft.world.phys.shapes.VoxelShape collision = cachedBlock.cachedCollisionShape;
+                if (collision == null) {
+                    collision = blockState.getConstantCollisionShape();
+                    if (collision == null) {
+                        collision = blockState.getCollisionShape(this.level, currPos, context);
+                        if (!context.isDelegated()) {
+                            // if it was not delegated during this call, assume that for any future ones it will not be delegated
+                            // again, and cache the result
+                            cachedBlock.cachedCollisionShape = collision;
+                        }
+                    } else {
+                        cachedBlock.cachedCollisionShape = collision;
+                    }
+                }
+
+                if (!collision.isEmpty() && collision.clip(from, to, currPos) != null) {
+                    return true;
+                }
+            }
+
+            if (normalizedCurrX > 1.0 && normalizedCurrY > 1.0 && normalizedCurrZ > 1.0) {
+                return false;
+            }
+
+            // inc the smallest normalized coordinate
+
+            if (normalizedCurrX < normalizedCurrY) {
+                if (normalizedCurrX < normalizedCurrZ) {
+                    currX += dx;
+                    normalizedCurrX += normalizedDiffX;
+                } else {
+                    // x < y && x >= z <--> z < y && z <= x
+                    currZ += dz;
+                    normalizedCurrZ += normalizedDiffZ;
+                }
+            } else if (normalizedCurrY < normalizedCurrZ) {
+                // y <= x && y < z
+                currY += dy;
+                normalizedCurrY += normalizedDiffY;
+            } else {
+                // y <= x && z <= y <--> z <= y && z <= x
+                currZ += dz;
+                normalizedCurrZ += normalizedDiffZ;
+            }
+        }
+    }
+
+    private float getSeenFraction(final Vec3 source, final Entity target,
+                                   final ExplosionBlockCache[] blockCache,
+                                   final BlockPos.MutableBlockPos blockPos) {
+        final AABB boundingBox = target.getBoundingBox();
+        final double diffX = boundingBox.maxX - boundingBox.minX;
+        final double diffY = boundingBox.maxY - boundingBox.minY;
+        final double diffZ = boundingBox.maxZ - boundingBox.minZ;
+
+        final double incX = 1.0 / (diffX * 2.0 + 1.0);
+        final double incY = 1.0 / (diffY * 2.0 + 1.0);
+        final double incZ = 1.0 / (diffZ * 2.0 + 1.0);
+
+        if (incX < 0.0 || incY < 0.0 || incZ < 0.0) {
+            return 0.0f;
+        }
+
+        final double offX = (1.0 - Math.floor(1.0 / incX) * incX) * 0.5 + boundingBox.minX;
+        final double offY = boundingBox.minY;
+        final double offZ = (1.0 - Math.floor(1.0 / incZ) * incZ) * 0.5 + boundingBox.minZ;
+
+        final io.papermc.paper.util.CollisionUtil.LazyEntityCollisionContext context = new io.papermc.paper.util.CollisionUtil.LazyEntityCollisionContext(target);
+
+        int totalRays = 0;
+        int missedRays = 0;
+
+        for (double dx = 0.0; dx <= 1.0; dx += incX) {
+            final double fromX = Math.fma(dx, diffX, offX);
+            for (double dy = 0.0; dy <= 1.0; dy += incY) {
+                final double fromY = Math.fma(dy, diffY, offY);
+                for (double dz = 0.0; dz <= 1.0; dz += incZ) {
+                    ++totalRays;
+
+                    final Vec3 from = new Vec3(
+                            fromX,
+                            fromY,
+                            Math.fma(dz, diffZ, offZ)
+                    );
+
+                    if (!this.clipsAnything(from, source, context, blockCache, blockPos)) {
+                        ++missedRays;
+                    }
+                }
+            }
+        }
+
+        return (float)missedRays / (float)totalRays;
+    }
+    // Paper end - optimise collisions
+
     private ExplosionDamageCalculator makeDamageCalculator(@Nullable Entity entity) {
         return (ExplosionDamageCalculator) (entity == null ? Explosion.EXPLOSION_DAMAGE_CALCULATOR : new EntityBasedExplosionDamageCalculator(entity));
     }
@@ -149,40 +414,90 @@ public class Explosion {
         int i;
         int j;
 
-        for (int k = 0; k < 16; ++k) {
-            for (i = 0; i < 16; ++i) {
-                for (j = 0; j < 16; ++j) {
-                    if (k == 0 || k == 15 || i == 0 || i == 15 || j == 0 || j == 15) {
-                        double d0 = (double) ((float) k / 15.0F * 2.0F - 1.0F);
-                        double d1 = (double) ((float) i / 15.0F * 2.0F - 1.0F);
-                        double d2 = (double) ((float) j / 15.0F * 2.0F - 1.0F);
-                        double d3 = Math.sqrt(d0 * d0 + d1 * d1 + d2 * d2);
-
-                        d0 /= d3;
-                        d1 /= d3;
-                        d2 /= d3;
+        // Paper start - optimise explosions
+        this.blockCache = new it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap<>();
+
+        this.chunkPosCache = new long[CHUNK_CACHE_WIDTH * CHUNK_CACHE_WIDTH];
+        java.util.Arrays.fill(this.chunkPosCache, ChunkPos.INVALID_CHUNK_POS);
+
+        this.chunkCache = new net.minecraft.world.level.chunk.LevelChunk[CHUNK_CACHE_WIDTH * CHUNK_CACHE_WIDTH];
+
+        final ExplosionBlockCache[] blockCache = new ExplosionBlockCache[BLOCK_EXPLOSION_CACHE_WIDTH * BLOCK_EXPLOSION_CACHE_WIDTH * BLOCK_EXPLOSION_CACHE_WIDTH];
+        // use initial cache value that is most likely to be used: the source position
+        final ExplosionBlockCache initialCache;
+        {
+            final int blockX = Mth.floor(this.x);
+            final int blockY = Mth.floor(this.y);
+            final int blockZ = Mth.floor(this.z);
+
+            final long key = BlockPos.asLong(blockX, blockY, blockZ);
+
+            initialCache = this.getOrCacheExplosionBlock(blockX, blockY, blockZ, key, true);
+        }
+        // only ~1/3rd of the loop iterations in vanilla will result in a ray, as it is iterating the perimeter of
+        // a 16x16x16 cube
+        // we can cache the rays and their normals as well, so that we eliminate the excess iterations / checks and
+        // calculations in one go
+        // additional aggressive caching of block retrieval is very significant, as at low power (i.e tnt) most
+        // block retrievals are not unique
+        for (int ray = 0, len = CACHED_RAYS.length; ray < len;) {
+            {
+                {
+                    {
+                        ExplosionBlockCache cachedBlock = initialCache;
+
+                        double d0 = CACHED_RAYS[ray];
+                        double d1 = CACHED_RAYS[ray + 1];
+                        double d2 = CACHED_RAYS[ray + 2];
+                        ray += 3;
+                        // Paper end - optimise explosions
                         float f = this.radius * (0.7F + this.level.random.nextFloat() * 0.6F);
                         double d4 = this.x;
                         double d5 = this.y;
                         double d6 = this.z;
 
                         for (float f1 = 0.3F; f > 0.0F; f -= 0.22500001F) {
-                            BlockPos blockposition = BlockPos.containing(d4, d5, d6);
-                            BlockState iblockdata = this.level.getBlockState(blockposition);
-                            if (!iblockdata.isDestroyable()) continue; // Paper
-                            FluidState fluid = iblockdata.getFluidState(); // Paper
+                            // Paper start - optimise explosions
+                            final int blockX = Mth.floor(d4);
+                            final int blockY = Mth.floor(d5);
+                            final int blockZ = Mth.floor(d6);
+
+                            final long key = BlockPos.asLong(blockX, blockY, blockZ);
+
+                            if (cachedBlock.key != key) {
+                                final int cacheKey =
+                                    (blockX & BLOCK_EXPLOSION_CACHE_MASK) |
+                                        (blockY & BLOCK_EXPLOSION_CACHE_MASK) << (BLOCK_EXPLOSION_CACHE_SHIFT) |
+                                        (blockZ & BLOCK_EXPLOSION_CACHE_MASK) << (BLOCK_EXPLOSION_CACHE_SHIFT + BLOCK_EXPLOSION_CACHE_SHIFT);
+                                cachedBlock = blockCache[cacheKey];
+                                if (cachedBlock == null || cachedBlock.key != key) {
+                                    blockCache[cacheKey] = cachedBlock = this.getOrCacheExplosionBlock(blockX, blockY, blockZ, key, true);
+                                }
+                            }
 
-                            if (!this.level.isInWorldBounds(blockposition)) {
+                            if (cachedBlock.outOfWorld) {
                                 break;
                             }
 
-                            Optional<Float> optional = this.damageCalculator.getBlockExplosionResistance(this, this.level, blockposition, iblockdata, fluid);
+                            BlockPos blockposition = cachedBlock.immutablePos;
+                            BlockState iblockdata = cachedBlock.blockState;
+                            // Paper end - optimise explosions
 
-                            if (optional.isPresent()) {
-                                f -= ((Float) optional.get() + 0.3F) * 0.3F;
-                            }
+                            if (!iblockdata.isDestroyable()) continue; // Paper
+                            // Paper - optimise explosions
 
-                            if (f > 0.0F && this.damageCalculator.shouldBlockExplode(this, this.level, blockposition, iblockdata, f)) {
+                            // Paper - optimise explosions
+
+                            f -= cachedBlock.resistance; // Paper - optimise explosions
+
+                            if (f > 0.0F && cachedBlock.shouldExplode == null) { // Paper - optimise explosions
+                                // Paper start - optimise explosions
+                                // note: we expect shouldBlockExplode to be pure with respect to power, as Vanilla currently is.
+                                // basically, it is unused, which allows us to cache the result
+                                final boolean shouldExplode = this.damageCalculator.shouldBlockExplode(this, this.level, cachedBlock.immutablePos, cachedBlock.blockState, f);
+                                cachedBlock.shouldExplode = shouldExplode ? Boolean.TRUE : Boolean.FALSE;
+                                if (shouldExplode && (this.fire || !cachedBlock.blockState.isAir())) {
+                                // Paper end - optimise explosions
                                 set.add(blockposition);
                                 // Paper start - prevent headless pistons from forming
                                 if (!io.papermc.paper.configuration.GlobalConfiguration.get().unsupportedSettings.allowHeadlessPistons && iblockdata.getBlock() == Blocks.MOVING_PISTON) {
@@ -193,11 +508,12 @@ public class Explosion {
                                     }
                                 }
                                 // Paper end
+                                } // Paper - optimise explosions
                             }
 
-                            d4 += d0 * 0.30000001192092896D;
-                            d5 += d1 * 0.30000001192092896D;
-                            d6 += d2 * 0.30000001192092896D;
+                            d4 += d0; // Paper - optimise explosions
+                            d5 += d1; // Paper - optimise explosions
+                            d6 += d2; // Paper - optimise explosions
                         }
                     }
                 }
@@ -217,6 +533,8 @@ public class Explosion {
         Vec3 vec3d = new Vec3(this.x, this.y, this.z);
         Iterator iterator = list.iterator();
 
+        final BlockPos.MutableBlockPos blockPos = new BlockPos.MutableBlockPos(); // Paper - optimise explosions
+
         while (iterator.hasNext()) {
             Entity entity = (Entity) iterator.next();
 
@@ -233,7 +551,7 @@ public class Explosion {
                         d8 /= d11;
                         d9 /= d11;
                         d10 /= d11;
-                        double d12 = this.getBlockDensity(vec3d, entity); // Paper - Optimize explosions
+                        double d12 = this.getBlockDensity(vec3d, entity, blockCache, blockPos); // Paper - Optimize explosions // Paper - optimise explosions
                         double d13 = (1.0D - d7) * d12;
 
                         // CraftBukkit start
@@ -256,7 +574,7 @@ public class Explosion {
                                 // Calculate damage separately for each EntityComplexPart
                                 double d7part;
                                 if (list.contains(entityComplexPart) && (d7part = Math.sqrt(entityComplexPart.distanceToSqr(vec3d)) / f2) <= 1.0D) {
-                                    double d13part = (1.0D - d7part) * Explosion.getSeenPercent(vec3d, entityComplexPart);
+                                    double d13part = (1.0D - d7part) * this.getSeenFraction(vec3d, entityComplexPart, blockCache, blockPos); // Paper - optimise explosions
                                     entityComplexPart.hurt(this.getDamageSource(), (float) ((int) ((d13part * d13part + d13part) / 2.0D * 7.0D * (double) f2 + 1.0D)));
                                 }
                             }
@@ -297,6 +615,10 @@ public class Explosion {
             }
         }
 
+        this.blockCache = null; // Paper - optimise explosions
+        this.chunkPosCache = null; // Paper - optimise explosions
+        this.chunkCache = null; // Paper - optimise explosions
+
     }
 
     public void finalizeExplosion(boolean particles) {
@@ -526,14 +848,14 @@ public class Explosion {
         private BlockInteraction() {}
     }
     // Paper start - Optimize explosions
-    private float getBlockDensity(Vec3 vec3d, Entity entity) {
+    private float getBlockDensity(Vec3 vec3d, Entity entity, ExplosionBlockCache[] blockCache, BlockPos.MutableBlockPos blockPos) { // Paper - optimise explosions
         if (!this.level.paperConfig().environment.optimizeExplosions) {
-            return getSeenPercent(vec3d, entity);
+            return this.getSeenFraction(vec3d, entity, blockCache, blockPos); // Paper - optimise explosions
         }
         CacheKey key = new CacheKey(this, entity.getBoundingBox());
         Float blockDensity = this.level.explosionDensityCache.get(key);
         if (blockDensity == null) {
-            blockDensity = getSeenPercent(vec3d, entity);
+            blockDensity = this.getSeenFraction(vec3d, entity, blockCache, blockPos); // Paper - optimise explosions;
             this.level.explosionDensityCache.put(key, blockDensity);
         }