Leaf/leaf-server/minecraft-patches/features/0216-Use-BFS-on-getSlopeDistance.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Taiyou06 <kaandindar21@gmail.com>
Date: Wed, 19 Mar 2025 18:41:56 +0100
Subject: [PATCH] Use BFS on getSlopeDistance

Uses Breadth First Search (BFS) to optimize getSlopeDistance
Paper: ~75ms
Leaf: ~48ms (-36%)
This should help drastically on the farms that use actively changing fluids.

diff --git a/net/minecraft/server/level/ServerLevel.java b/net/minecraft/server/level/ServerLevel.java
index 56e6691f4fc425f13fe5f1fd40de16f4c54a3195..f77bd9472300aec6958ebfa69469fb4e1ee36484 100644
--- a/net/minecraft/server/level/ServerLevel.java
+++ b/net/minecraft/server/level/ServerLevel.java
@@ -1438,6 +1438,10 @@ public class ServerLevel extends Level implements ServerEntityGetter, WorldGenLe
         this.emptyTime = 0;
     }
 
+    // Leaf start - Use BFS on getSlopeDistance
+    public it.unimi.dsi.fastutil.longs.LongSet slopeDistanceCacheVisited = new it.unimi.dsi.fastutil.longs.LongOpenHashSet(512);
+    public net.minecraft.world.level.material.FlowingFluid.SlopeDistanceNodeDeque slopeDistanceCacheQueue = new net.minecraft.world.level.material.FlowingFluid.SlopeDistanceNodeDeque();
+    // Leaf end - Use BFS on getSlopeDistance
     private void tickFluid(BlockPos pos, Fluid fluid) {
         BlockState blockState = this.getBlockState(pos);
         FluidState fluidState = blockState.getFluidState();
diff --git a/net/minecraft/world/level/material/FlowingFluid.java b/net/minecraft/world/level/material/FlowingFluid.java
index 4fe1b3fc6304a2a404fd0f62f52fc792bcd5dfaf..a00c38b0d6b6d32af4ab3e926705b0f2594157dd 100644
--- a/net/minecraft/world/level/material/FlowingFluid.java
+++ b/net/minecraft/world/level/material/FlowingFluid.java
@@ -342,32 +342,124 @@ public abstract class FlowingFluid extends Fluid {
 
     protected abstract void beforeDestroyingBlock(LevelAccessor level, BlockPos pos, BlockState state);
 
-    protected int getSlopeDistance(LevelReader level, BlockPos pos, int depth, Direction direction, BlockState state, FlowingFluid.SpreadContext spreadContext) {
-        int i = 1000;
+    // Leaf start - Use BFS on getSlopeDistance
+    protected int getSlopeDistance(LevelReader level, BlockPos startPos, int initialDepth, Direction excludedDirection, BlockState startState, FlowingFluid.SpreadContext spreadContext) {
+        it.unimi.dsi.fastutil.longs.LongSet visited = ((ServerLevel) level).slopeDistanceCacheVisited;
+        SlopeDistanceNodeDeque queue = ((ServerLevel) level).slopeDistanceCacheQueue;
+        visited.clear();
+        queue.clear();
+
+        for (Direction dir : Direction.Plane.HORIZONTAL) {
+            if (dir == excludedDirection) continue;
+
+            BlockPos neighborPos = startPos.relative(dir); // immutable
+            BlockState neighborState = spreadContext.getBlockStateIfLoaded(neighborPos);
+            if (neighborState == null) continue;
+
+            // Check if the fluid can actually pass through to this first neighbor before adding
+            FluidState neighborFluidState = neighborState.getFluidState();
+            if (!this.canPassThrough(level, this.getFlowing(), startPos, startState, dir, neighborPos, neighborState, neighborFluidState)) {
+                continue;
+            }
+            long visitKey = encodeSlopeNode(neighborPos, dir.getOpposite());
+            if (visited.add(visitKey)) {
+                queue.add(new FlowingFluid.SlopeDistanceNode(neighborPos, initialDepth, dir.getOpposite(), neighborState));
+            }
+        }
 
-        for (Direction direction1 : Direction.Plane.HORIZONTAL) {
-            if (direction1 != direction) {
-                BlockPos blockPos = pos.relative(direction1);
-                BlockState blockState = spreadContext.getBlockStateIfLoaded(blockPos); // Paper - Prevent chunk loading from fluid flowing
-                if (blockState == null) continue; // Paper - Prevent chunk loading from fluid flowing
-                FluidState fluidState = blockState.getFluidState();
-                if (this.canPassThrough(level, this.getFlowing(), pos, state, direction1, blockPos, blockState, fluidState)) {
-                    if (spreadContext.isHole(blockPos)) {
-                        return depth;
-                    }
+        int slopeFindDistance = this.getSlopeFindDistance(level);
+        int minDistance = 1000;
 
-                    if (depth < this.getSlopeFindDistance(level)) {
-                        int slopeDistance = this.getSlopeDistance(level, blockPos, depth + 1, direction1.getOpposite(), blockState, spreadContext);
-                        if (slopeDistance < i) {
-                            i = slopeDistance;
-                        }
-                    }
+        // Process the queue
+        while (!queue.isEmpty()) {
+            FlowingFluid.SlopeDistanceNode current = queue.poll();
+            if (spreadContext.isHole(current.pos)) {
+                return current.depth;
+            }
+
+            if (current.depth >= slopeFindDistance) continue;
+
+            for (Direction dir : Direction.Plane.HORIZONTAL) {
+                if (dir == current.excludedDir) continue;
+
+                BlockPos nextPos = current.pos.relative(dir); // immutable
+                BlockState nextState = spreadContext.getBlockStateIfLoaded(nextPos);
+                if (nextState == null) continue;
+
+                FluidState nextFluidState = nextState.getFluidState();
+                if (!this.canPassThrough(level, this.getFlowing(), current.pos, current.state, dir, nextPos, nextState, nextFluidState)) {
+                    continue;
+                }
+
+                long visitKey = encodeSlopeNode(nextPos, dir.getOpposite());
+                if (visited.add(visitKey)) {
+                    queue.add(new FlowingFluid.SlopeDistanceNode(nextPos, current.depth + 1, dir.getOpposite(), nextState));
                 }
             }
         }
 
-        return i;
+        return minDistance;
+    }
+
+    private static long encodeSlopeNode(BlockPos pos, Direction excludedDir) {
+        return ((long) pos.getX() & 0xFFFFFFFFL) << 32 | ((long) pos.getZ() & 0xFFFFFFFFL) << 4 | (excludedDir.ordinal() & 0x0F);
+    }
+
+    public static class SlopeDistanceNodeDeque {
+        private SlopeDistanceNode[] array;
+        private int length;
+        private int start;
+        private int end;
+
+        public SlopeDistanceNodeDeque() {
+            array = new SlopeDistanceNode[256];
+            length = array.length;
+        }
+
+            /*
+        private int size() {
+            int apparent = end - start;
+            return apparent >= 0 ? apparent : length + apparent;
+        }
+        */
+
+        private void clear() {
+            start = 0;
+            end = 0;
+        }
+
+        private boolean isEmpty() {
+            return end == start || (end <= start && length == start - end);
+        }
+
+        private SlopeDistanceNode poll() {
+            final SlopeDistanceNode t = array[start];
+            if (++start == length) start = 0;
+            return t;
+        }
+
+        private void add(final SlopeDistanceNode node) {
+            array[end++] = node;
+            if (end == length) end = 0;
+            if (end == start) resize(length, 2 * length);
+        }
+
+        private void resize(final int size, final int newLength) {
+            final SlopeDistanceNode[] newArray = new SlopeDistanceNode[newLength];
+            if (size != 0) {
+                System.arraycopy(array, start, newArray, 0, length - start);
+                System.arraycopy(array, 0, newArray, length - start, end);
+            }
+            start = 0;
+            end = size;
+            array = newArray;
+            length = newLength;
+        }
+    }
+
+    private record SlopeDistanceNode(BlockPos pos, int depth, Direction excludedDir, BlockState state) {
     }
+    // Leaf end - Use BFS on getSlopeDistance
 
     boolean isWaterHole(BlockGetter level, BlockPos pos, BlockState state, BlockPos belowPos, BlockState belowState) {
         return canPassThroughWall(Direction.DOWN, level, pos, state, belowPos, belowState)