From c3dd4a6a7983efc266830dec7e308ec425dee334 Mon Sep 17 00:00:00 2001
From: Martin Panzer <postremus1996@googlemail.com>
Date: Fri, 3 Jun 2016 23:13:39 +0200
Subject: [PATCH] Fix FallingBlocks being stuck on fences

Fallingblocks would previously only check if directly beneath them a block exists. They also
hover on top of the 1.5 block tall hitbox of fences during these check. This
resulted in them always thinking they would be on air.

We now first check, if if we are already on the ground.
if not, we check if the falling block is inside of the hitbox of the block at y - 1.

diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
index d2a542354..c74071eb1 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -336,4 +336,9 @@ public class PaperWorldConfig {
         preventTntFromMovingInWater = getBoolean("prevent-tnt-from-moving-in-water", false);
         log("Prevent TNT from moving in water: " + preventTntFromMovingInWater);
     }
+
+    public boolean altFallingBlockOnGround;
+    private void altFallingBlockOnGround() {
+        altFallingBlockOnGround = getBoolean("use-alternate-fallingblock-onGround-detection", false);
+    }
 }
diff --git a/src/main/java/net/minecraft/server/BlockFalling.java b/src/main/java/net/minecraft/server/BlockFalling.java
index 674395756..1086e3117 100644
--- a/src/main/java/net/minecraft/server/BlockFalling.java
+++ b/src/main/java/net/minecraft/server/BlockFalling.java
@@ -71,6 +71,12 @@ public class BlockFalling extends Block {
         return block == Blocks.FIRE || material == Material.AIR || material == Material.WATER || material == Material.LAVA;
     }
 
+    // Paper start - OBFHELPER
+    public static boolean canMoveThrough(IBlockData blockdata) {
+        return BlockFalling.x(blockdata);
+    }
+    // Paper end
+
     public void a(World world, BlockPosition blockposition, IBlockData iblockdata, IBlockData iblockdata1) {}
 
     public void a_(World world, BlockPosition blockposition) {}
diff --git a/src/main/java/net/minecraft/server/EntityFallingBlock.java b/src/main/java/net/minecraft/server/EntityFallingBlock.java
index 70a196461..3c7bdccc4 100644
--- a/src/main/java/net/minecraft/server/EntityFallingBlock.java
+++ b/src/main/java/net/minecraft/server/EntityFallingBlock.java
@@ -3,6 +3,7 @@ package net.minecraft.server;
 import com.google.common.collect.Lists;
 import java.util.ArrayList;
 import java.util.Iterator;
+import java.util.List;
 import javax.annotation.Nullable;
 
 import org.bukkit.craftbukkit.event.CraftEventFactory; // CraftBukkit
@@ -120,10 +121,10 @@ public class EntityFallingBlock extends Entity {
                     }
                 } else {
                     IBlockData iblockdata = this.world.getType(blockposition);
-
-                    if (!flag1 && BlockFalling.x(this.world.getType(new BlockPosition(this.locX, this.locY - 0.009999999776482582D, this.locZ)))) {
+                    
+                    if (!isOnGround()) {
                         this.onGround = false;
-                        // return; // CraftBukkit
+                        if (this.world.paperConfig.altFallingBlockOnGround) return; // Paper
                     }
 
                     this.motX *= 0.699999988079071D;
@@ -179,6 +180,32 @@ public class EntityFallingBlock extends Entity {
         }
     }
 
+    // Paper start
+    private boolean isOnGround() {
+        BlockPosition where = new BlockPosition(this.locX, this.locY - 0.009999999776482582D, this.locZ);
+        boolean cannotMoveThrough = !BlockFalling.canMoveThrough(this.world.getType(where));
+        if (!this.world.paperConfig.altFallingBlockOnGround) return cannotMoveThrough;
+
+        if (cannotMoveThrough) {
+            return true;
+        }
+
+        IBlockData blockData = this.world.getType(where.down());
+        if (BlockFalling.canMoveThrough(blockData)) {
+            return false;
+        }
+
+        List<AxisAlignedBB> list = new ArrayList<>();
+        addCollisions(blockData, getWorld(), where, this.getBoundingBox(), list, this);
+        return list.size() > 0;
+    }
+
+    // OBFHELPER
+    private void addCollisions(IBlockData blockData, World world, BlockPosition where, AxisAlignedBB collider, List<AxisAlignedBB> list, Entity entity) {
+        blockData.a(world, where, collider, list, entity, false);
+    }
+    // Paper end
+
     public void e(float f, float f1) {
         Block block = this.block.getBlock();
 
-- 
2.13.0