From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Paul Sauve <paul@technove.co>
Date: Sat, 31 Oct 2020 18:43:02 -0500
Subject: [PATCH] Strip raytracing for EntityLiving#hasLineOfSight

The BlockGetter#clip method is very wasteful in both allocations,
and in logic. While EntityLiving#hasLineOfSight provides static
parameters for collisions with blocks and fluids, the method still does
a lot of dynamic checks for both of these, which result in extra work.
As well, since the fluid collision option is set to NONE, the entire
fluid collision system is completely unneeded, yet used anyways.

Copyright (C) 2020 Technove LLC

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.

diff --git a/src/main/java/net/minecraft/world/entity/LivingEntity.java b/src/main/java/net/minecraft/world/entity/LivingEntity.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/world/entity/LivingEntity.java
+++ b/src/main/java/net/minecraft/world/entity/LivingEntity.java
@@ -0,0 +0,0 @@ public abstract class LivingEntity extends Entity implements Attackable {
             Vec3 vec3d1 = new Vec3(entity.getX(), entity.getEyeY(), entity.getZ());
 
             // Paper - diff on change - used in CraftLivingEntity#hasLineOfSight(Location) and CraftWorld#lineOfSightExists
-            return vec3d1.distanceToSqr(vec3d) > 128.0D * 128.0D ? false : this.level().clip(new ClipContext(vec3d, vec3d1, ClipContext.Block.COLLIDER, ClipContext.Fluid.NONE, this)).getType() == HitResult.Type.MISS; // Paper - Perf: Use distance squared
+            return vec3d1.distanceToSqr(vec3d) > 128.0D * 128.0D ? false : this.level().clipDirect(vec3d, vec3d1, net.minecraft.world.phys.shapes.CollisionContext.of(this)) == HitResult.Type.MISS; // Paper - Perf: Use distance squared & strip raytracing
         }
     }
 
diff --git a/src/main/java/net/minecraft/world/level/BlockGetter.java b/src/main/java/net/minecraft/world/level/BlockGetter.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/world/level/BlockGetter.java
+++ b/src/main/java/net/minecraft/world/level/BlockGetter.java
@@ -0,0 +0,0 @@ public interface BlockGetter extends LevelHeightAccessor {
         });
     }
 
+    // Paper start - Broken down variant of the method below, used by Level#clipDirect
+    @Nullable
+    default BlockHitResult.Type clipDirect(Vec3 start, Vec3 end, BlockPos pos, BlockState state, net.minecraft.world.phys.shapes.CollisionContext collisionContext) {
+        if (state.isAir()) {
+            return null;
+        }
+
+        final VoxelShape voxelshape = ClipContext.Block.COLLIDER.get(state, this, pos, collisionContext);
+        final BlockHitResult hitResult = this.clipWithInteractionOverride(start, end, pos, voxelshape, state);
+        return hitResult == null ? null : hitResult.getType();
+    }
+    // Paper end
     // CraftBukkit start - moved block handling into separate method for use by Block#rayTrace
     default BlockHitResult clip(ClipContext raytrace1, BlockPos blockposition) {
         // Paper start - Add predicate for blocks when raytracing
diff --git a/src/main/java/net/minecraft/world/level/Level.java b/src/main/java/net/minecraft/world/level/Level.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/world/level/Level.java
+++ b/src/main/java/net/minecraft/world/level/Level.java
@@ -0,0 +0,0 @@ public abstract class Level implements LevelAccessor, AutoCloseable, ca.spottedl
         return null;
     }
 
-    // Paper start
+    // Paper start - Broken down method of raytracing for EntityLiving#hasLineOfSight, replaces BlockGetter#clip(CollisionContext)
     public net.minecraft.world.phys.BlockHitResult.Type clipDirect(Vec3 start, Vec3 end, net.minecraft.world.phys.shapes.CollisionContext context) {
-        // To be patched over
-        return this.clip(new ClipContext(start, end, ClipContext.Block.COLLIDER, ClipContext.Fluid.NONE, context)).getType();
+        // most of this code comes from BlockGetter#clip(CollisionContext, BiFunction, Function), but removes the needless functions
+        if (start.equals(end)) {
+            return net.minecraft.world.phys.BlockHitResult.Type.MISS;
+        }
+
+        final double endX = Mth.lerp(-1.0E-7D, end.x, start.x);
+        final double endY = Mth.lerp(-1.0E-7D, end.y, start.y);
+        final double endZ = Mth.lerp(-1.0E-7D, end.z, start.z);
+
+        final double startX = Mth.lerp(-1.0E-7D, start.x, end.x);
+        final double startY = Mth.lerp(-1.0E-7D, start.y, end.y);
+        final double startZ = Mth.lerp(-1.0E-7D, start.z, end.z);
+
+        int currentX = Mth.floor(startX);
+        int currentY = Mth.floor(startY);
+        int currentZ = Mth.floor(startZ);
+
+        final BlockPos.MutableBlockPos currentBlock = new BlockPos.MutableBlockPos(currentX, currentY, currentZ);
+
+        LevelChunk chunk = this.getChunkIfLoaded(currentBlock);
+        if (chunk == null) {
+            return net.minecraft.world.phys.BlockHitResult.Type.MISS;
+        }
+
+        final net.minecraft.world.phys.BlockHitResult.Type initialCheck = this.clipDirect(start, end, currentBlock, chunk.getBlockState(currentBlock), context);
+        if (initialCheck != null) {
+            return initialCheck;
+        }
+
+        final double diffX = endX - startX;
+        final double diffY = endY - startY;
+        final double diffZ = endZ - startZ;
+
+        final int xDirection = Mth.sign(diffX);
+        final int yDirection = Mth.sign(diffY);
+        final int zDirection = Mth.sign(diffZ);
+
+        final double normalizedX = xDirection == 0 ? Double.MAX_VALUE : (double) xDirection / diffX;
+        final double normalizedY = yDirection == 0 ? Double.MAX_VALUE : (double) yDirection / diffY;
+        final double normalizedZ = zDirection == 0 ? Double.MAX_VALUE : (double) zDirection / diffZ;
+
+        double normalizedXDirection = normalizedX * (xDirection > 0 ? 1.0D - Mth.frac(startX) : Mth.frac(startX));
+        double normalizedYDirection = normalizedY * (yDirection > 0 ? 1.0D - Mth.frac(startY) : Mth.frac(startY));
+        double normalizedZDirection = normalizedZ * (zDirection > 0 ? 1.0D - Mth.frac(startZ) : Mth.frac(startZ));
+
+        net.minecraft.world.phys.BlockHitResult.Type result;
+
+        do {
+            if (normalizedXDirection > 1.0D && normalizedYDirection > 1.0D && normalizedZDirection > 1.0D) {
+                return net.minecraft.world.phys.BlockHitResult.Type.MISS;
+            }
+
+            if (normalizedXDirection < normalizedYDirection) {
+                if (normalizedXDirection < normalizedZDirection) {
+                    currentX += xDirection;
+                    normalizedXDirection += normalizedX;
+                } else {
+                    currentZ += zDirection;
+                    normalizedZDirection += normalizedZ;
+                }
+            } else if (normalizedYDirection < normalizedZDirection) {
+                currentY += yDirection;
+                normalizedYDirection += normalizedY;
+            } else {
+                currentZ += zDirection;
+                normalizedZDirection += normalizedZ;
+            }
+
+            currentBlock.set(currentX, currentY, currentZ);
+            if (chunk.getPos().x != currentBlock.getX() >> 4 || chunk.getPos().z != currentBlock.getZ() >> 4) {
+                chunk = this.getChunkIfLoaded(currentBlock);
+                if (chunk == null) {
+                    return net.minecraft.world.phys.BlockHitResult.Type.MISS;
+                }
+            }
+            result = this.clipDirect(start, end, currentBlock, chunk.getBlockState(currentBlock), context);
+        } while (result == null);
+
+        return result;
     }
     // Paper end
 
