From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: JellySquid <jellysquid+atwork@protonmail.com>
Date: Sat, 9 May 2020 16:25:21 -0400
Subject: [PATCH] Implement JellySquid's Entity Collision optimisations patch

Optimizes Full Block voxel collisions, and removes streams from Entity collisions

Original code by JellySquid, licensed under GNU Lesser General Public License v3.0
you can find the original code on https://github.com/jellysquid3/lithium-fabric/tree/1.15.x/fabric (Yarn mappings)

diff --git a/src/main/java/net/minecraft/server/ICollisionAccess.java b/src/main/java/net/minecraft/server/ICollisionAccess.java
index 8b0670b8db0bb739fb54fee368a53eadeb72937e..c501dad733b6e6fe89673b35a307e02d474570b6 100644
--- a/src/main/java/net/minecraft/server/ICollisionAccess.java
+++ b/src/main/java/net/minecraft/server/ICollisionAccess.java
@@ -113,11 +113,24 @@ public interface ICollisionAccess extends IBlockAccess {
 
                             if ((j2 != 1 || iblockdata.f()) && (j2 != 2 || iblockdata.getBlock() == Blocks.MOVING_PISTON)) {
                                 VoxelShape voxelshape2 = iblockdata.b((IBlockAccess) ICollisionAccess.this, blockposition_mutableblockposition, voxelshapecollision);
-                                VoxelShape voxelshape3 = voxelshape2.a((double) k1, (double) l1, (double) i2);
 
-                                if (VoxelShapes.c(voxelshape, voxelshape3, OperatorBoolean.AND)) {
-                                    consumer.accept(voxelshape3);
-                                    return true;
+                                // Paper start - Lithium Collision Optimizations
+                                if (voxelshape2 == VoxelShapes.empty()) {
+                                    continue;
+                                }
+
+                                if (voxelshape2 == VoxelShapes.fullCube()) {
+                                    if (axisalignedbb.intersects(x, y, z, x + 1.0D, y + 1.0D, z + 1.0D)) {
+                                        consumer.accept(voxelshape2.offset(x, y, z));
+                                        return true;
+                                    }
+                                } else {
+                                    VoxelShape shape = voxelshape2.offset(x, y, z);
+                                    if (VoxelShapes.applyOperation(shape, voxelshape, OperatorBoolean.AND)) {
+                                        consumer.accept(shape);
+                                        return true;
+                                    }
+                                    // Paper end
                                 }
                             }
                         }
diff --git a/src/main/java/net/minecraft/server/IEntityAccess.java b/src/main/java/net/minecraft/server/IEntityAccess.java
index 5135308fb6137a34ed6fd061f0a210de6de4e81c..d434aaaaf0ab6a18ab0fe5ad0bf8ed4662f49120 100644
--- a/src/main/java/net/minecraft/server/IEntityAccess.java
+++ b/src/main/java/net/minecraft/server/IEntityAccess.java
@@ -52,20 +52,41 @@ public interface IEntityAccess {
     // Paper end - optimise hard collision
 
     default Stream<VoxelShape> b(@Nullable Entity entity, AxisAlignedBB axisalignedbb, Set<Entity> set) {
-        if (axisalignedbb.a() < 1.0E-7D) {
+        // Paper start - remove streams from entity collision
+        if (axisalignedbb.getAverageSideLength() < 1.0E-7D) {
             return Stream.empty();
-        } else {
-            AxisAlignedBB axisalignedbb1 = axisalignedbb.g(1.0E-7D);
-            Stream<AxisAlignedBB> stream = ((entity != null && entity.hardCollides()) ? this.getEntities(entity, axisalignedbb) : this.getHardCollidingEntities(entity, axisalignedbb1)).stream().filter((entity1) -> { // Paper - decompile fix // Paper - optimise hard collision
-                return !set.contains(entity1);
-            }).filter((entity1) -> {
-                return entity == null || !entity.isSameVehicle(entity1);
-            }).flatMap((entity1) -> {
-                return Stream.of(entity1.au(), entity == null ? null : entity.j(entity1)); // Paper - optimise hard collision - diff on change, these are the methods that only hard colliding entities override
-            }).filter(Objects::nonNull);
-
-            return stream.filter(axisalignedbb1::c).map(VoxelShapes::a);
+
         }
+        AxisAlignedBB selection = axisalignedbb.grow(1.0E-7D);
+        List<Entity> entities = entity != null && entity.hardCollides() ? getEntities(entity, selection) : getHardCollidingEntities(entity, selection);
+        List<VoxelShape> shapes = new java.util.ArrayList<>();
+
+        for (Entity otherEntity : entities) {
+            if (!set.isEmpty() && set.contains(otherEntity)) {
+                continue;
+            }
+
+            if (entity != null && entity.isSameVehicle(otherEntity)) {
+                continue;
+            }
+
+            AxisAlignedBB otherEntityBox = otherEntity.getCollisionBox();
+
+            if (otherEntityBox != null && selection.intersects(otherEntityBox)) {
+                shapes.add(VoxelShapes.of(otherEntityBox));
+            }
+
+            if (entity != null) {
+                AxisAlignedBB otherEntityHardBox = entity.getHardCollisionBox(otherEntity);
+
+                if (otherEntityHardBox != null && selection.intersects(otherEntityHardBox)) {
+                    shapes.add(VoxelShapes.of(otherEntityHardBox));
+                }
+            }
+        }
+
+        return shapes.stream();
+        // Paper end
     }
 
     @Nullable