From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Thu, 2 Apr 2020 02:37:57 -0400
Subject: [PATCH] Optimize Collision to not load chunks

The collision code takes an AABB and generates a cuboid of checks rather
than a cylinder, so at high velocity this can generate a lot of chunk checks.

Treat an unloaded chunk as a collision for entities, and also for players if
the "prevent moving into unloaded chunks" setting is enabled.

If that serting is not enabled, collisions will be ignored for players, since
movement will load only the chunk the player enters anyways and avoids loading
massive amounts of surrounding chunks due to large AABB lookups.

diff --git a/src/main/java/net/minecraft/server/ICollisionAccess.java b/src/main/java/net/minecraft/server/ICollisionAccess.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/ICollisionAccess.java
+++ b/src/main/java/net/minecraft/server/ICollisionAccess.java
@@ -0,0 +0,0 @@ public interface ICollisionAccess extends IBlockAccess {
                 }
 
                 while (cursorposition.a()) {
-                    int k1 = cursorposition.b();
-                    int l1 = cursorposition.c();
-                    int i2 = cursorposition.d();
+                    int k1 = cursorposition.b();int x = k1; // Paper
+                    int l1 = cursorposition.c();int y = l1; // Paper
+                    int i2 = cursorposition.d();int z = i2; // Paper
                     int j2 = cursorposition.e();
 
                     if (j2 != 3) {
+                        // Paper start - ensure we don't load chunks
                         int k2 = k1 >> 4;
                         int l2 = i2 >> 4;
-                        IBlockAccess iblockaccess = ICollisionAccess.this.c(k2, l2);
-
-                        if (iblockaccess != null) {
-                            blockposition_mutableblockposition.d(k1, l1, i2);
-                            IBlockData iblockdata = iblockaccess.getType(blockposition_mutableblockposition);
+                        boolean far = entity != null && MCUtil.distance(entity.locX(), entity.locY(), entity.locZ(), x, y, z) > 8;
+                        blockposition_mutableblockposition.setValues(x, y, z);
+
+                        boolean isRegionLimited = ICollisionAccess.this instanceof RegionLimitedWorldAccess;
+                        IBlockData iblockdata = !isRegionLimited ? ICollisionAccess.this.getTypeIfLoaded(blockposition_mutableblockposition) : null;
+                        if ((isRegionLimited || !far) && iblockdata == null) {
+                            IBlockAccess c = ICollisionAccess.this.c(k2, l2);
+                            if (c != null) {
+                                iblockdata = c.getType(blockposition_mutableblockposition);
+                            }
+                        }
+                        if (iblockdata == null) {
+                            if (!(entity instanceof EntityPlayer) || entity.world.paperConfig.preventMovingIntoUnloadedChunks) {
+                                VoxelShape voxelshape3 = VoxelShapes.of(far ? entity.getBoundingBox() : new AxisAlignedBB(new BlockPosition(x, y, z)));
+                                consumer.accept(voxelshape3);
+                                return true;
+                            }
+                        } else {
+                            //blockposition_mutableblockposition.d(k1, l1, i2); // moved up
+                            //IBlockData iblockdata = iblockaccess.getType(blockposition_mutableblockposition); // moved up
+                            // Paper end
 
                             if ((j2 != 1 || iblockdata.f()) && (j2 != 2 || iblockdata.getBlock() == Blocks.MOVING_PISTON)) {
                                 VoxelShape voxelshape2 = iblockdata.b((IBlockAccess) ICollisionAccess.this, blockposition_mutableblockposition, voxelshapecollision);
diff --git a/src/main/java/net/minecraft/server/PlayerList.java b/src/main/java/net/minecraft/server/PlayerList.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/PlayerList.java
+++ b/src/main/java/net/minecraft/server/PlayerList.java
@@ -0,0 +0,0 @@ public abstract class PlayerList {
         entityplayer1.forceSetPositionRotation(location.getX(), location.getY(), location.getZ(), location.getYaw(), location.getPitch());
         // CraftBukkit end
 
+        location.getChunk(); // Paper - force load chunk to be sure getCubes works
         while (avoidSuffocation && !worldserver.getCubes(entityplayer1) && entityplayer1.locY() < 256.0D) {
             entityplayer1.setPosition(entityplayer1.locX(), entityplayer1.locY() + 1.0D, entityplayer1.locZ());
         }
diff --git a/src/main/java/net/minecraft/server/VoxelShapes.java b/src/main/java/net/minecraft/server/VoxelShapes.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/VoxelShapes.java
+++ b/src/main/java/net/minecraft/server/VoxelShapes.java
@@ -0,0 +0,0 @@ public final class VoxelShapes {
 
                             if (k2 < 3) {
                                 blockposition_mutableblockposition.a(enumaxiscycle1, i2, j2, l1);
-                                IBlockData iblockdata = iworldreader.getType(blockposition_mutableblockposition);
+                                IBlockData iblockdata = iworldreader.getTypeIfLoaded(blockposition_mutableblockposition); // Paper
+                                if (iblockdata == null) return 0.0D; // Paper
 
                                 if ((k2 != 1 || iblockdata.f()) && (k2 != 2 || iblockdata.getBlock() == Blocks.MOVING_PISTON)) {
                                     d0 = iblockdata.b((IBlockAccess) iworldreader, blockposition_mutableblockposition, voxelshapecollision).a(enumdirection_enumaxis2, axisalignedbb.d((double) (-blockposition_mutableblockposition.getX()), (double) (-blockposition_mutableblockposition.getY()), (double) (-blockposition_mutableblockposition.getZ())), d0);