Workaround for entity pathfinding in inverted gravity

src/main/java/com/minelittlepony/unicopia/entity/RotatedView.java

@@ -0,0 +1,32 @@
+package com.minelittlepony.unicopia.entity;
+
+import net.minecraft.util.math.BlockPos;
+
+public interface RotatedView {
+
+    void setRotationCenter(int y, int increments);
+
+    int getRotationY();
+
+    int getRotationIncrements();
+
+    default void clearRotation() {
+        setRotationCenter(0, 0);
+    }
+
+    default BlockPos applyRotation(BlockPos pos) {
+        int newY = applyRotation(pos.getY());
+        if (newY == pos.getY()) {
+            return pos;
+        }
+        return new BlockPos(pos.getX(), applyRotation(pos.getY()), pos.getZ());
+    }
+
+    default int applyRotation(int y) {
+        if (getRotationIncrements() == 0) {
+            return y;
+        }
+        return y - ((y - getRotationY()) * 2);
+    }
+
+}

src/main/java/com/minelittlepony/unicopia/mixin/MixinMobEntity.java

@@ -8,7 +8,9 @@ import org.spongepowered.asm.mixin.injection.Inject;
 import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
 import com.minelittlepony.unicopia.entity.Creature;
 import com.minelittlepony.unicopia.entity.PonyContainer;
+import com.minelittlepony.unicopia.entity.RotatedView;
 import com.minelittlepony.unicopia.entity.Equine;
+import com.minelittlepony.unicopia.entity.Living;
 
 import net.minecraft.entity.EntityType;
 import net.minecraft.entity.LivingEntity;
@@ -29,4 +31,18 @@ abstract class MixinMobEntity extends LivingEntity implements PonyContainer<Equi
     private void init(EntityType<? extends MobEntity> entityType, World world, CallbackInfo info) {
         ((Creature)get()).initAi(goalSelector, targetSelector);
     }
+
+    @Inject(method = "tickNewAi", at = @At("HEAD"))
+    public void beforeTickAi(CallbackInfo into) {
+        Equine<?> eq = Equine.of(this);
+
+        if (eq instanceof Living<?> && eq.getPhysics().isGravityNegative()) {
+            ((RotatedView)world).setRotationCenter((int)getY(), 1);
+        }
+    }
+
+    @Inject(method = "tickNewAi", at = @At("RETURN"))
+    public void afterTickAi(CallbackInfo into) {
+        ((RotatedView)world).clearRotation();
+    }
 }

src/main/java/com/minelittlepony/unicopia/mixin/MixinServerWorld.java

@@ -6,6 +6,7 @@ import org.spongepowered.asm.mixin.injection.Inject;
 import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
 
 import com.minelittlepony.unicopia.BlockDestructionManager;
+
 import net.minecraft.block.BlockState;
 import net.minecraft.server.world.ServerWorld;
 import net.minecraft.util.math.BlockPos;

src/main/java/com/minelittlepony/unicopia/mixin/MixinWorld.java

@@ -9,6 +9,7 @@ import javax.annotation.Nullable;
 import org.spongepowered.asm.mixin.Mixin;
 
 import com.minelittlepony.unicopia.BlockDestructionManager;
+import com.minelittlepony.unicopia.entity.RotatedView;
 import com.minelittlepony.unicopia.entity.behaviour.Disguise;
 
 import net.minecraft.entity.Entity;
@@ -18,10 +19,30 @@ import net.minecraft.world.World;
 import net.minecraft.world.WorldAccess;
 
 @Mixin(World.class)
-abstract class MixinWorld implements WorldAccess, BlockDestructionManager.Source {
+abstract class MixinWorld implements WorldAccess, BlockDestructionManager.Source, RotatedView {
 
     private final BlockDestructionManager destructions = new BlockDestructionManager((World)(Object)this);
 
+    private int rotationY;
+    private int rotationIncrements;
+
+    @Override
+    public void setRotationCenter(int y, int increments) {
+        rotationY = y;
+        rotationIncrements = increments;
+    }
+
+    @Override
+    public int getRotationY() {
+        return rotationY;
+    }
+
+    @Override
+    public int getRotationIncrements() {
+        return rotationIncrements;
+    }
+
+
     @Override
     public BlockDestructionManager getDestructionManager() {
         return destructions;

src/main/java/com/minelittlepony/unicopia/mixin/MixinWorldChunk.java

@@ -0,0 +1,30 @@
+package com.minelittlepony.unicopia.mixin;
+
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.ModifyVariable;
+
+import com.minelittlepony.unicopia.entity.RotatedView;
+
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.world.chunk.WorldChunk;
+
+@Mixin(WorldChunk.class)
+abstract class MixinWorldChunk {
+
+    @ModifyVariable(method = {
+            "getBlockState(Lnet/minecraft/util/math/BlockPos;)Lnet/minecraft/block/BlockState;",
+            "setBlockState(Lnet/minecraft/util/math/BlockPos;)V",
+            "getBlockEntity(Lnet/minecraft/util/math/BlockPos;Lnet/minecraft/world/chunk/WorldChunk$CreationType;)Lnet/minecraft/block/entity/BlockEntity;",
+            "setBlockEntity(Lnet/minecraft/util/math/BlockPos;Lnet/minecraft/block/entity/BlockEntity;)V",
+            "removeBlockEntity(Lnet/minecraft/util/math/BlockPos;)V",
+    }, at = @At("HEAD"))
+    private BlockPos modifyBlockPos(BlockPos pos) {
+        return ((RotatedView)((WorldChunk)(Object)this).getWorld()).applyRotation(pos);
+    }
+
+    @ModifyVariable(method = "getFluidState(III)Lnet/minecraft/fluid/FluidState;", at = @At("HEAD"), ordinal = 1)
+    private int modifyFluidPos(int y) {
+        return ((RotatedView)((WorldChunk)(Object)this).getWorld()).applyRotation(y);
+    }
+}