Rework clipping logic again, now works as well as the original implementation

src/main/java/net/minecraft/server/Entity.java

@@ -22,9 +22,65 @@ import org.bukkit.event.entity.EntityDamageByBlockEvent;
 import org.bukkit.event.entity.EntityDamageByEntityEvent;
 import org.bukkit.event.entity.EntityDamageEvent;
 import org.bukkit.plugin.PluginManager;
+import org.bukkit.util.NumberConversions;
 // CraftBukkit end
 
 public abstract class Entity {
+    // CraftBukkit start -  size of entity for clipping calculations
+    public enum EntitySize {
+        SIZE_1,
+        SIZE_2,
+        SIZE_3,
+        SIZE_4,
+        SIZE_5,
+        SIZE_6;
+
+        public int getXZCoord(double loc) {
+            double diff = loc - (NumberConversions.floor(loc) + 0.5D);
+
+            switch (this) {
+            case SIZE_1:
+                if (diff < 0.0D ? diff < -0.3125D : diff < 0.3125D) {
+                    return NumberConversions.ceil(loc * 32.0D);
+                }
+
+                return NumberConversions.floor(loc * 32.0D);
+            case SIZE_2:
+                if (diff < 0.0D ? diff < -0.3125D : diff < 0.3125D) {
+                    return NumberConversions.floor(loc * 32.0D);
+                }
+
+                return NumberConversions.ceil(loc * 32.0D);
+            case SIZE_3:
+                if (diff > 0.0D) {
+                    return NumberConversions.floor(loc * 32.0D);
+                }
+
+                return NumberConversions.ceil(loc * 32.0D);
+            case SIZE_4:
+                if (diff < 0.0D ? diff < -0.1875D : diff < 0.1875D) {
+                    return NumberConversions.ceil(loc * 32.0D);
+                }
+
+                return NumberConversions.floor(loc * 32.0D);
+            case SIZE_5:
+                if (diff < 0.0D ? diff < -0.1875D : diff < 0.1875D) {
+                    return NumberConversions.floor(loc * 32.0D);
+                }
+
+                return NumberConversions.ceil(loc * 32.0D);
+            case SIZE_6:
+            default:
+                if (diff > 0.0D) {
+                    return NumberConversions.ceil(loc * 32.0D);
+                }
+
+                return NumberConversions.floor(loc * 32.0D);
+            }
+        }
+    }
+    public EntitySize size;
+    // CraftBukkit end
 
     private static int entityCount = 0;
     public int id;
@@ -100,6 +156,7 @@ public abstract class Entity {
         this.dead = false;
         this.height = 0.0F;
         this.width = 0.6F;
+        this.size = EntitySize.SIZE_2; // CraftBukkit
         this.length = 1.8F;
         this.bI = 0.0F;
         this.bJ = 0.0F;
@@ -147,6 +204,22 @@ public abstract class Entity {
     protected void b(float f, float f1) {
         this.width = f;
         this.length = f1;
+        // CraftBukkit start - figure out entity size for clipping calculations
+        float mod = f % 2f;
+        if (mod < 0.375) {
+            this.size = EntitySize.SIZE_1;
+        } else if (mod < 0.75) {
+            this.size = EntitySize.SIZE_2;
+        } else if (mod < 1.0) {
+            this.size = EntitySize.SIZE_3;
+        } else if (mod < 1.375) {
+            this.size = EntitySize.SIZE_4;
+        } else if (mod < 1.75) {
+            this.size = EntitySize.SIZE_5;
+        } else {
+            this.size = EntitySize.SIZE_6;
+        }
+        // CraftBukkit end
     }
 
     protected void c(float f, float f1) {

src/main/java/net/minecraft/server/EntityTrackerEntry.java

@@ -6,8 +6,6 @@ import java.util.Iterator;
 import java.util.List;
 import java.util.Set;
 
-import org.bukkit.util.NumberConversions; // Craftbukkit
-
 public class EntityTrackerEntry {
 
     public Entity tracker;
@@ -66,29 +64,10 @@ public class EntityTrackerEntry {
 
         ++this.u;
         if (this.m++ % this.c == 0 || this.tracker.ce) {
-            // CraftBukkit start - Add logic for clipping;
+            // CraftBukkit start - add logic for clipping
-            boolean xFlag = NumberConversions.floor(this.tracker.locX) - this.tracker.locX > -.5d;
+            int i = this.tracker.size.getXZCoord(this.tracker.locX);
-            boolean zFlag = NumberConversions.floor(this.tracker.locZ) - this.tracker.locZ > -.5d;
+            int j = org.bukkit.util.NumberConversions.floor(this.tracker.locY * 32.0D);
-            if ((this.tracker.width % 2f) >= 1f) {
+            int k = this.tracker.size.getXZCoord(this.tracker.locZ);
-                xFlag = !xFlag;
-                zFlag = !zFlag;
-            }
-
-            int i;
-            int j = NumberConversions.ceil(this.tracker.locY * 32.0D);;
-            int k;
-
-            if (xFlag) {
-                i = NumberConversions.ceil(this.tracker.locX * 32.0D);
-            } else {
-                i = NumberConversions.floor(this.tracker.locX * 32.0D);
-            }
-
-            if (zFlag) {
-                k = NumberConversions.ceil(this.tracker.locZ * 32.0D);
-            } else {
-                k = NumberConversions.floor(this.tracker.locZ * 32.0D);
-            }
             // CraftBukkit end - logic for clipping
 
             int l = MathHelper.d(this.tracker.yaw * 256.0F / 360.0F);
@@ -124,7 +103,7 @@ public class EntityTrackerEntry {
             } else {
                 this.u = 0;
                 // CraftBukkit start
-                // remove (redundant?) setting of entity location to avoid clipping through blocks
+                // remove setting of entity location to avoid clipping through blocks
                 //this.tracker.locX = (double) i / 32.0D;
                 //this.tracker.locY = (double) j / 32.0D;
                 //this.tracker.locZ = (double) k / 32.0D;
@@ -133,7 +112,7 @@ public class EntityTrackerEntry {
                 if (this.tracker instanceof EntityPlayer) {
                     this.scanPlayers(new ArrayList(this.trackedPlayers));
                 }
-                object = new Packet34EntityTeleport(this.tracker.id, i, j, k, (byte) l, (byte) i1); // move entities down 1 client side so they don't clip up out of boxes
+                object = new Packet34EntityTeleport(this.tracker.id, i, j, k, (byte) l, (byte) i1);
                 // CraftBukkit end
             }
 

src/main/java/net/minecraft/server/Packet24MobSpawn.java

@@ -24,9 +24,11 @@ public class Packet24MobSpawn extends Packet {
     public Packet24MobSpawn(EntityLiving entityliving) {
         this.a = entityliving.id;
         this.b = (byte) EntityTypes.a((Entity) entityliving);
-        this.c = MathHelper.floor(entityliving.locX * 32.0D);
+        // CraftBukkit start - floors to new intelligence
-        this.d = MathHelper.floor(entityliving.locY * 32.0D);
+        this.c = entityliving.size.getXZCoord(entityliving.locX);
-        this.e = MathHelper.floor(entityliving.locZ * 32.0D);
+        this.d = org.bukkit.util.NumberConversions.floor(entityliving.locY * 32.0D);
+        this.e = entityliving.size.getXZCoord(entityliving.locZ);
+        // CraftBukkit end
         this.f = (byte) ((int) (entityliving.yaw * 256.0F / 360.0F));
         this.g = (byte) ((int) (entityliving.pitch * 256.0F / 360.0F));
         this.h = (byte) ((int) (entityliving.X * 256.0F / 360.0F));