From eb001bde1cff971c9a4e667ed42fb1bee8dc491c Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Thu, 1 Nov 2018 19:45:51 -0400
Subject: [PATCH] Optimize Small Entity Movement

Optimizes small movements by entities by merging the movement
into the entities next larger movement, until enough movement
velocity has been hit.

This reduces collision detection and able to reduce movement
cpu cost by 5-7%.

The default option of 0.75 seems to provide all the gains without
any noticable behavior change to entity movement.

We have to exclude slimes due to weird jumping animation bugs.

diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
index eabb2c1bad..f6d4c476bc 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -569,4 +569,10 @@ public class PaperWorldConfig {
     private void preventMovingIntoUnloadedChunks() {
         preventMovingIntoUnloadedChunks = getBoolean("prevent-moving-into-unloaded-chunks", false);
     }
+
+    public double mergeEntityMovement = 0.075D;
+    private void mergeEntityMovement() {
+        mergeEntityMovement = getDouble("merge-entity-movement", mergeEntityMovement);
+    }
+
 }
diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
index 32b90f30d9..6023824e3d 100644
--- a/src/main/java/net/minecraft/server/Entity.java
+++ b/src/main/java/net/minecraft/server/Entity.java
@@ -558,6 +558,15 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
 
     }
 
+    // Paper start
+    protected double pendingX = 0D;
+    protected double pendingY = 0D;
+    protected double pendingZ = 0D;
+    public boolean shouldMergeMovement(double mergeMin, double d0, double d1, double d2) {
+        return d0 * d0 < mergeMin && d1 * d1 < mergeMin && d2 * d2 < mergeMin;
+    }
+    // Paper end
+
     public void extinguish() {
         this.fireTicks = 0;
     }
@@ -580,6 +589,23 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
             this.a(this.getBoundingBox().d(d0, d1, d2));
             this.recalcPosition();
         } else {
+            // Paper start
+            final double mergeMin = this.world.paperConfig.mergeEntityMovement;
+            if (mergeMin > 0 && enummovetype == EnumMoveType.SELF) {
+                if (pendingX != 0D) {
+                    d0 += pendingX;
+                    pendingX = 0D;
+                }
+                if (pendingY != 0D) {
+                    d1 += pendingY;
+                    pendingY = 0D;
+                }
+                if (pendingZ != 0D) {
+                    d2 += pendingZ;
+                    pendingZ = 0D;
+                }
+            }
+            // Paper end
             if (enummovetype == EnumMoveType.PISTON) {
                 this.activatedTick = MinecraftServer.currentTick + 20; // Paper
                 long i = this.world.getTime();
@@ -683,6 +709,17 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
                 }
             }
 
+            // Paper start
+            if (mergeMin > 0 && enummovetype == EnumMoveType.SELF && shouldMergeMovement(mergeMin, d0, d1, d2)) {
+                pendingX = d0;
+                pendingY = d1;
+                pendingZ = d2;
+                d0 = d7 = 0;
+                d1 = d8 = 0;
+                d2 = d9 = 0;
+            }
+            // Paper end
+
             AxisAlignedBB axisalignedbb = this.getBoundingBox();
 
             if (d0 != 0.0D || d1 != 0.0D || d2 != 0.0D) {
diff --git a/src/main/java/net/minecraft/server/EntitySlime.java b/src/main/java/net/minecraft/server/EntitySlime.java
index e63f4afa9b..1941faaebd 100644
--- a/src/main/java/net/minecraft/server/EntitySlime.java
+++ b/src/main/java/net/minecraft/server/EntitySlime.java
@@ -495,6 +495,12 @@ public class EntitySlime extends EntityInsentient implements IMonster {
     }
 
     // Paper start
+    @Override
+    public boolean shouldMergeMovement(double mergeMin, double d0, double d1, double d2) {
+        // Slimes have weird movement bugs when a move is skipped, ideally we can fix this and fix that state
+        return false;
+    }
+
     private boolean canWander = true;
     public boolean canWander() {
         return canWander;
-- 
2.19.1