Merge 94de2e79cd into 9fd3bf2d0f

core/pom.xml

@@ -119,6 +119,11 @@
             <artifactId>holographicdisplays-nms-v1_20_r2</artifactId>
         </dependency>
 
+        <dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>holographicdisplays-nms-v1_20_r3</artifactId>
+        </dependency>
+
         <dependency>
             <groupId>org.spigotmc</groupId>
             <artifactId>spigot-api</artifactId>

core/src/main/java/me/filoghost/holographicdisplays/core/NMSVersion.java

@@ -42,7 +42,8 @@ public enum NMSVersion {
     /* 1.19.3          */ v1_19_R2(errorCollector -> new me.filoghost.holographicdisplays.nms.v1_19_R2.VersionNMSManager(errorCollector)),
     /* 1.19.4          */ v1_19_R3(errorCollector -> new me.filoghost.holographicdisplays.nms.v1_19_R3.VersionNMSManager(errorCollector)),
     /* 1.20 - 1.20.1   */ v1_20_R1(errorCollector -> new me.filoghost.holographicdisplays.nms.v1_20_R1.VersionNMSManager(errorCollector)),
-    /* 1.20.2 - ?      */ v1_20_R2(errorCollector -> new me.filoghost.holographicdisplays.nms.v1_20_R2.VersionNMSManager(errorCollector)),
+    /* 1.20.2          */ v1_20_R2(errorCollector -> new me.filoghost.holographicdisplays.nms.v1_20_R2.VersionNMSManager(errorCollector)),
+    /* 1.20.3 - 1.20.4 */ v1_20_R3(errorCollector -> new me.filoghost.holographicdisplays.nms.v1_20_R3.VersionNMSManager(errorCollector)),
     /* Other versions  */ UNKNOWN(NMSManagerFactory.unknownVersion());
 
     private static final NMSVersion CURRENT_VERSION = detectCurrentVersion();

nms/pom.xml

@@ -32,6 +32,7 @@
         <module>v1_19_r3</module>
         <module>v1_20_r1</module>
         <module>v1_20_r2</module>
+        <module>v1_20_r3</module>
     </modules>
 
     <dependencies>

nms/v1_20_r3/pom.xml

@@ -0,0 +1,36 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>me.filoghost.holographicdisplays</groupId>
+        <artifactId>holographicdisplays-nms</artifactId>
+        <version>3.0.4-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>holographicdisplays-nms-v1_20_r3</artifactId>
+    <name>HolographicDisplays NMS v1_20_R3</name>
+
+    <dependencies>
+        <dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>holographicdisplays-nms-common</artifactId>
+        </dependency>
+
+        <dependency>
+            <groupId>org.spigotmc</groupId>
+            <artifactId>spigot</artifactId>
+            <version>1.20.4-R0.1-SNAPSHOT</version>
+            <scope>provided</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>org.joml</groupId>
+            <artifactId>joml</artifactId>
+            <version>1.10.5</version>
+            <scope>provided</scope>
+        </dependency>
+    </dependencies>
+
+</project>

nms/v1_20_r3/src/main/java/me/filoghost/holographicdisplays/nms/v1_20_R3/DataWatcherKey.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) filoghost and contributors
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package me.filoghost.holographicdisplays.nms.v1_20_R3;
+
+import io.netty.handler.codec.EncoderException;
+import net.minecraft.network.chat.IChatBaseComponent;
+import net.minecraft.network.syncher.DataWatcherRegistry;
+import net.minecraft.network.syncher.DataWatcherSerializer;
+import net.minecraft.world.item.ItemStack;
+
+import java.util.Optional;
+
+class DataWatcherKey<T> {
+
+    private static final DataWatcherSerializer<Byte> BYTE_SERIALIZER = DataWatcherRegistry.a;
+    private static final DataWatcherSerializer<Integer> INT_SERIALIZER = DataWatcherRegistry.b;
+    private static final DataWatcherSerializer<Boolean> BOOLEAN_SERIALIZER = DataWatcherRegistry.k;
+    private static final DataWatcherSerializer<ItemStack> ITEM_STACK_SERIALIZER = DataWatcherRegistry.h;
+    private static final DataWatcherSerializer<Optional<IChatBaseComponent>> OPTIONAL_CHAT_COMPONENT_SERIALIZER = DataWatcherRegistry.g;
+
+    static final DataWatcherKey<Byte> ENTITY_STATUS = new DataWatcherKey<>(0, BYTE_SERIALIZER);
+    static final DataWatcherKey<Optional<IChatBaseComponent>> CUSTOM_NAME = new DataWatcherKey<>(2, OPTIONAL_CHAT_COMPONENT_SERIALIZER);
+    static final DataWatcherKey<Boolean> CUSTOM_NAME_VISIBILITY = new DataWatcherKey<>(3, BOOLEAN_SERIALIZER);
+    static final DataWatcherKey<ItemStack> ITEM_STACK = new DataWatcherKey<>(8, ITEM_STACK_SERIALIZER);
+    static final DataWatcherKey<Byte> ARMOR_STAND_STATUS = new DataWatcherKey<>(15, BYTE_SERIALIZER);
+    static final DataWatcherKey<Integer> SLIME_SIZE = new DataWatcherKey<>(16, INT_SERIALIZER);
+
+    private final int index;
+    private final DataWatcherSerializer<T> serializer;
+    private final int serializerTypeID;
+
+    private DataWatcherKey(int index, DataWatcherSerializer<T> serializer) {
+        this.index = index;
+        this.serializer = serializer;
+        this.serializerTypeID = DataWatcherRegistry.b(serializer);
+        if (serializerTypeID < 0) {
+            throw new EncoderException("Could not find serializer ID of " + serializer);
+        }
+    }
+
+    int getIndex() {
+        return index;
+    }
+
+    DataWatcherSerializer<T> getSerializer() {
+        return serializer;
+    }
+
+    int getSerializerTypeID() {
+        return serializerTypeID;
+    }
+
+}

nms/v1_20_r3/src/main/java/me/filoghost/holographicdisplays/nms/v1_20_R3/DataWatcherPacketBuilder.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) filoghost and contributors
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package me.filoghost.holographicdisplays.nms.v1_20_R3;
+
+import me.filoghost.fcommons.Strings;
+import net.minecraft.network.chat.IChatBaseComponent;
+import org.bukkit.craftbukkit.v1_20_R3.inventory.CraftItemStack;
+import org.bukkit.craftbukkit.v1_20_R3.util.CraftChatMessage;
+import org.bukkit.inventory.ItemStack;
+
+import java.util.Optional;
+
+abstract class DataWatcherPacketBuilder<T> {
+
+    private static final int MAX_CUSTOM_NAME_LENGTH = 5000;
+
+    private final PacketByteBuffer packetByteBuffer;
+
+    DataWatcherPacketBuilder(PacketByteBuffer packetByteBuffer) {
+        this.packetByteBuffer = packetByteBuffer;
+    }
+
+    DataWatcherPacketBuilder<T> setInvisible() {
+        packetByteBuffer.writeDataWatcherEntry(DataWatcherKey.ENTITY_STATUS, (byte) 0x20); // Invisible
+        return this;
+    }
+
+    DataWatcherPacketBuilder<T> setArmorStandMarker() {
+        setInvisible();
+        packetByteBuffer.writeDataWatcherEntry(
+                DataWatcherKey.ARMOR_STAND_STATUS, (byte) (0x01 | 0x02 | 0x08 | 0x10)); // Small, no gravity, no base plate, marker
+        return this;
+    }
+
+    DataWatcherPacketBuilder<T> setCustomName(String customName) {
+        packetByteBuffer.writeDataWatcherEntry(DataWatcherKey.CUSTOM_NAME, getCustomNameDataWatcherValue(customName));
+        packetByteBuffer.writeDataWatcherEntry(DataWatcherKey.CUSTOM_NAME_VISIBILITY, !Strings.isEmpty(customName));
+        return this;
+    }
+
+    private Optional<IChatBaseComponent> getCustomNameDataWatcherValue(String customName) {
+        customName = Strings.truncate(customName, MAX_CUSTOM_NAME_LENGTH);
+        if (!Strings.isEmpty(customName)) {
+            return Optional.of(CraftChatMessage.fromString(customName, false, true)[0]);
+        } else {
+            return Optional.empty();
+        }
+    }
+
+    DataWatcherPacketBuilder<T> setItemStack(ItemStack itemStack) {
+        packetByteBuffer.writeDataWatcherEntry(DataWatcherKey.ITEM_STACK, CraftItemStack.asNMSCopy(itemStack));
+        return this;
+    }
+
+    DataWatcherPacketBuilder<T> setSlimeSmall() {
+        packetByteBuffer.writeDataWatcherEntry(DataWatcherKey.SLIME_SIZE, 1);
+        return this;
+    }
+
+    T build() {
+        packetByteBuffer.writeDataWatcherEntriesEnd();
+        return createPacket(packetByteBuffer);
+    }
+
+    abstract T createPacket(PacketByteBuffer packetByteBuffer);
+
+}

nms/v1_20_r3/src/main/java/me/filoghost/holographicdisplays/nms/v1_20_R3/EntityDestroyNMSPacket.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) filoghost and contributors
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package me.filoghost.holographicdisplays.nms.v1_20_R3;
+
+import me.filoghost.holographicdisplays.nms.common.EntityID;
+import net.minecraft.network.protocol.Packet;
+import net.minecraft.network.protocol.game.PacketPlayOutEntityDestroy;
+
+class EntityDestroyNMSPacket extends VersionNMSPacket {
+
+    private final Packet<?> rawPacket;
+
+    EntityDestroyNMSPacket(EntityID entityID) {
+        PacketByteBuffer packetByteBuffer = PacketByteBuffer.get();
+
+        packetByteBuffer.writeVarIntArray(entityID.getNumericID());
+
+        this.rawPacket = new PacketPlayOutEntityDestroy(packetByteBuffer.getInternalSerializer());
+    }
+
+    EntityDestroyNMSPacket(EntityID entityID1, EntityID entityID2) {
+        PacketByteBuffer packetByteBuffer = PacketByteBuffer.get();
+
+        packetByteBuffer.writeVarIntArray(entityID1.getNumericID(), entityID2.getNumericID());
+
+        this.rawPacket = new PacketPlayOutEntityDestroy(packetByteBuffer.getInternalSerializer());
+    }
+
+    @Override
+    Packet<?> getRawPacket() {
+        return rawPacket;
+    }
+
+}

nms/v1_20_r3/src/main/java/me/filoghost/holographicdisplays/nms/v1_20_R3/EntityMetadataNMSPacket.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) filoghost and contributors
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package me.filoghost.holographicdisplays.nms.v1_20_R3;
+
+import me.filoghost.holographicdisplays.nms.common.EntityID;
+import net.minecraft.network.protocol.Packet;
+import net.minecraft.network.protocol.game.PacketPlayOutEntityMetadata;
+
+class EntityMetadataNMSPacket extends VersionNMSPacket {
+
+    private final Packet<?> rawPacket;
+
+    private EntityMetadataNMSPacket(PacketByteBuffer packetByteBuffer) {
+        this.rawPacket = new PacketPlayOutEntityMetadata(packetByteBuffer.getInternalSerializer());
+    }
+
+    @Override
+    Packet<?> getRawPacket() {
+        return rawPacket;
+    }
+
+    public static DataWatcherPacketBuilder<EntityMetadataNMSPacket> builder(EntityID entityID) {
+        PacketByteBuffer packetByteBuffer = PacketByteBuffer.get();
+        packetByteBuffer.writeVarInt(entityID.getNumericID());
+        return new Builder(packetByteBuffer);
+    }
+
+
+    private static class Builder extends DataWatcherPacketBuilder<EntityMetadataNMSPacket> {
+
+        private Builder(PacketByteBuffer packetByteBuffer) {
+            super(packetByteBuffer);
+        }
+
+        @Override
+        EntityMetadataNMSPacket createPacket(PacketByteBuffer packetByteBuffer) {
+            return new EntityMetadataNMSPacket(packetByteBuffer);
+        }
+
+    }
+
+}

nms/v1_20_r3/src/main/java/me/filoghost/holographicdisplays/nms/v1_20_R3/EntityMountNMSPacket.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) filoghost and contributors
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package me.filoghost.holographicdisplays.nms.v1_20_R3;
+
+import me.filoghost.holographicdisplays.nms.common.EntityID;
+import net.minecraft.network.protocol.Packet;
+import net.minecraft.network.protocol.game.PacketPlayOutMount;
+
+class EntityMountNMSPacket extends VersionNMSPacket {
+
+    private final Packet<?> rawPacket;
+
+    EntityMountNMSPacket(EntityID vehicleEntityID, EntityID passengerEntityID) {
+        PacketByteBuffer packetByteBuffer = PacketByteBuffer.get();
+
+        packetByteBuffer.writeVarInt(vehicleEntityID.getNumericID());
+        packetByteBuffer.writeVarIntArray(passengerEntityID.getNumericID());
+
+        this.rawPacket = new PacketPlayOutMount(packetByteBuffer.getInternalSerializer());
+    }
+
+    @Override
+    Packet<?> getRawPacket() {
+        return rawPacket;
+    }
+
+}

nms/v1_20_r3/src/main/java/me/filoghost/holographicdisplays/nms/v1_20_R3/EntitySpawnNMSPacket.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) filoghost and contributors
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package me.filoghost.holographicdisplays.nms.v1_20_R3;
+
+import me.filoghost.holographicdisplays.common.PositionCoordinates;
+import me.filoghost.holographicdisplays.nms.common.EntityID;
+import net.minecraft.network.protocol.Packet;
+import net.minecraft.network.protocol.game.PacketPlayOutSpawnEntity;
+
+class EntitySpawnNMSPacket extends VersionNMSPacket {
+
+    private final Packet<?> rawPacket;
+
+    EntitySpawnNMSPacket(EntityID entityID, int entityTypeID, PositionCoordinates position, double positionOffsetY) {
+        PacketByteBuffer packetByteBuffer = PacketByteBuffer.get();
+
+        packetByteBuffer.writeVarInt(entityID.getNumericID());
+        packetByteBuffer.writeUUID(entityID.getUUID());
+        packetByteBuffer.writeVarInt(entityTypeID);
+
+        // Position
+        packetByteBuffer.writeDouble(position.getX());
+        packetByteBuffer.writeDouble(position.getY() + positionOffsetY);
+        packetByteBuffer.writeDouble(position.getZ());
+
+        // Rotation
+        packetByteBuffer.writeByte(0);
+        packetByteBuffer.writeByte(0);
+
+        // Object data
+        if (entityTypeID == EntityTypeID.ITEM) {
+            packetByteBuffer.writeInt(1); // Velocity is present and zero (otherwise by default a random velocity is applied)
+        } else {
+            packetByteBuffer.writeInt(0);
+        }
+
+        // Velocity
+        packetByteBuffer.writeShort(0);
+        packetByteBuffer.writeShort(0);
+        packetByteBuffer.writeShort(0);
+
+        this.rawPacket = new PacketPlayOutSpawnEntity(packetByteBuffer.getInternalSerializer());
+    }
+
+    @Override
+    Packet<?> getRawPacket() {
+        return rawPacket;
+    }
+
+}

nms/v1_20_r3/src/main/java/me/filoghost/holographicdisplays/nms/v1_20_R3/EntityTeleportNMSPacket.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) filoghost and contributors
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package me.filoghost.holographicdisplays.nms.v1_20_R3;
+
+import me.filoghost.holographicdisplays.common.PositionCoordinates;
+import me.filoghost.holographicdisplays.nms.common.EntityID;
+import net.minecraft.network.protocol.Packet;
+import net.minecraft.network.protocol.game.PacketPlayOutEntityTeleport;
+
+class EntityTeleportNMSPacket extends VersionNMSPacket {
+
+    private final Packet<?> rawPacket;
+
+    EntityTeleportNMSPacket(EntityID entityID, PositionCoordinates position, double positionOffsetY) {
+        PacketByteBuffer packetByteBuffer = PacketByteBuffer.get();
+
+        packetByteBuffer.writeVarInt(entityID.getNumericID());
+
+        // Position
+        packetByteBuffer.writeDouble(position.getX());
+        packetByteBuffer.writeDouble(position.getY() + positionOffsetY);
+        packetByteBuffer.writeDouble(position.getZ());
+
+        // Rotation
+        packetByteBuffer.writeByte(0);
+        packetByteBuffer.writeByte(0);
+
+        // On ground
+        packetByteBuffer.writeBoolean(false);
+
+        this.rawPacket = new PacketPlayOutEntityTeleport(packetByteBuffer.getInternalSerializer());
+    }
+
+    @Override
+    Packet<?> getRawPacket() {
+        return rawPacket;
+    }
+
+}

nms/v1_20_r3/src/main/java/me/filoghost/holographicdisplays/nms/v1_20_R3/EntityTypeID.java

@@ -0,0 +1,14 @@
+/*
+ * Copyright (C) filoghost and contributors
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package me.filoghost.holographicdisplays.nms.v1_20_R3;
+
+class EntityTypeID {
+
+    static final int ARMOR_STAND = 2;
+    static final int ITEM = 55;
+    static final int SLIME = 89;
+
+}

nms/v1_20_r3/src/main/java/me/filoghost/holographicdisplays/nms/v1_20_R3/InboundPacketHandler.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) filoghost and contributors
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package me.filoghost.holographicdisplays.nms.v1_20_R3;
+
+import io.netty.channel.ChannelHandlerContext;
+import io.netty.channel.ChannelInboundHandlerAdapter;
+import me.filoghost.fcommons.logging.Log;
+import me.filoghost.fcommons.reflection.ReflectField;
+import me.filoghost.holographicdisplays.nms.common.NMSErrors;
+import me.filoghost.holographicdisplays.nms.common.PacketListener;
+import net.minecraft.network.protocol.game.PacketPlayInUseEntity;
+import org.bukkit.entity.Player;
+
+class InboundPacketHandler extends ChannelInboundHandlerAdapter {
+
+    public static final String HANDLER_NAME = "holographic_displays_listener";
+    private static final ReflectField<Integer> ENTITY_ID_FIELD = ReflectField.lookup(int.class, PacketPlayInUseEntity.class, "a");
+
+    private final Player player;
+    private final PacketListener packetListener;
+
+    InboundPacketHandler(Player player, PacketListener packetListener) {
+        this.player = player;
+        this.packetListener = packetListener;
+    }
+
+    @Override
+    public void channelRead(ChannelHandlerContext context, Object packet) throws Exception {
+        try {
+            if (packet instanceof PacketPlayInUseEntity) {
+                int entityID = ENTITY_ID_FIELD.get(packet);
+                boolean cancel = packetListener.onAsyncEntityInteract(player, entityID);
+                if (cancel) {
+                    return;
+                }
+            }
+        } catch (Throwable t) {
+            Log.warning(NMSErrors.EXCEPTION_ON_PACKET_READ, t);
+        }
+        super.channelRead(context, packet);
+    }
+
+}

nms/v1_20_r3/src/main/java/me/filoghost/holographicdisplays/nms/v1_20_R3/PacketByteBuffer.java

@@ -0,0 +1,85 @@
+/*
+ * Copyright (C) filoghost and contributors
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package me.filoghost.holographicdisplays.nms.v1_20_R3;
+
+import io.netty.buffer.Unpooled;
+import net.minecraft.network.PacketDataSerializer;
+
+import java.util.UUID;
+
+class PacketByteBuffer {
+
+    private static final PacketByteBuffer INSTANCE = new PacketByteBuffer();
+
+    private final PacketDataSerializer serializer;
+
+    static PacketByteBuffer get() {
+        INSTANCE.clear();
+        return INSTANCE;
+    }
+
+    private PacketByteBuffer() {
+        this.serializer = new PacketDataSerializer(Unpooled.buffer());
+    }
+
+    void writeBoolean(boolean flag) {
+        serializer.writeBoolean(flag);
+    }
+
+    void writeByte(int i) {
+        serializer.writeByte(i);
+    }
+
+    void writeShort(int i) {
+        serializer.writeShort(i);
+    }
+
+    void writeInt(int i) {
+        serializer.writeInt(i);
+    }
+
+    void writeDouble(double d) {
+        serializer.writeDouble(d);
+    }
+
+    void writeVarInt(int i) {
+        serializer.c(i);
+    }
+
+    void writeVarIntArray(int i1) {
+        writeVarInt(1);
+        writeVarInt(i1);
+    }
+
+    void writeVarIntArray(int i1, int i2) {
+        writeVarInt(2);
+        writeVarInt(i1);
+        writeVarInt(i2);
+    }
+
+    void writeUUID(UUID uuid) {
+        serializer.a(uuid);
+    }
+
+    <T> void writeDataWatcherEntry(DataWatcherKey<T> key, T value) {
+        serializer.writeByte(key.getIndex());
+        writeVarInt(key.getSerializerTypeID());
+        key.getSerializer().a(serializer, value);
+    }
+
+    void writeDataWatcherEntriesEnd() {
+        serializer.writeByte(0xFF);
+    }
+
+    public PacketDataSerializer getInternalSerializer() {
+        return serializer;
+    }
+
+    void clear() {
+        serializer.clear();
+    }
+
+}

nms/v1_20_r3/src/main/java/me/filoghost/holographicdisplays/nms/v1_20_R3/VersionClickableNMSPacketEntity.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) filoghost and contributors
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package me.filoghost.holographicdisplays.nms.v1_20_R3;
+
+import me.filoghost.holographicdisplays.common.PositionCoordinates;
+import me.filoghost.holographicdisplays.nms.common.EntityID;
+import me.filoghost.holographicdisplays.nms.common.PacketGroup;
+import me.filoghost.holographicdisplays.nms.common.entity.ClickableNMSPacketEntity;
+
+class VersionClickableNMSPacketEntity implements ClickableNMSPacketEntity {
+
+    private final EntityID slimeID;
+
+    VersionClickableNMSPacketEntity(EntityID slimeID) {
+        this.slimeID = slimeID;
+    }
+
+    @Override
+    public EntityID getID() {
+        return slimeID;
+    }
+
+    @Override
+    public PacketGroup newSpawnPackets(PositionCoordinates position) {
+        return PacketGroup.of(
+                new EntitySpawnNMSPacket(slimeID, EntityTypeID.SLIME, position, SLIME_Y_OFFSET),
+                EntityMetadataNMSPacket.builder(slimeID)
+                        .setInvisible()
+                        .setSlimeSmall() // Required for a correct client-side collision box
+                        .build()
+        );
+    }
+
+    @Override
+    public PacketGroup newTeleportPackets(PositionCoordinates position) {
+        return new EntityTeleportNMSPacket(slimeID, position, SLIME_Y_OFFSET);
+    }
+
+    @Override
+    public PacketGroup newDestroyPackets() {
+        return new EntityDestroyNMSPacket(slimeID);
+    }
+
+}

nms/v1_20_r3/src/main/java/me/filoghost/holographicdisplays/nms/v1_20_R3/VersionItemNMSPacketEntity.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) filoghost and contributors
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package me.filoghost.holographicdisplays.nms.v1_20_R3;
+
+import me.filoghost.holographicdisplays.common.PositionCoordinates;
+import me.filoghost.holographicdisplays.nms.common.EntityID;
+import me.filoghost.holographicdisplays.nms.common.PacketGroup;
+import me.filoghost.holographicdisplays.nms.common.entity.ItemNMSPacketEntity;
+import org.bukkit.inventory.ItemStack;
+
+class VersionItemNMSPacketEntity implements ItemNMSPacketEntity {
+
+    private final EntityID itemID;
+    private final EntityID vehicleID;
+
+    VersionItemNMSPacketEntity(EntityID itemID, EntityID vehicleID) {
+        this.itemID = itemID;
+        this.vehicleID = vehicleID;
+    }
+
+    @Override
+    public PacketGroup newSpawnPackets(PositionCoordinates position, ItemStack itemStack) {
+        return PacketGroup.of(
+                new EntitySpawnNMSPacket(vehicleID, EntityTypeID.ARMOR_STAND, position, ITEM_Y_OFFSET),
+                EntityMetadataNMSPacket.builder(vehicleID)
+                        .setArmorStandMarker()
+                        .build(),
+                new EntitySpawnNMSPacket(itemID, EntityTypeID.ITEM, position, ITEM_Y_OFFSET),
+                EntityMetadataNMSPacket.builder(itemID)
+                        .setItemStack(itemStack)
+                        .build(),
+                new EntityMountNMSPacket(vehicleID, itemID)
+        );
+    }
+
+    @Override
+    public PacketGroup newChangePackets(ItemStack itemStack) {
+        return EntityMetadataNMSPacket.builder(itemID)
+                .setItemStack(itemStack)
+                .build();
+    }
+
+    @Override
+    public PacketGroup newTeleportPackets(PositionCoordinates position) {
+        return new EntityTeleportNMSPacket(vehicleID, position, ITEM_Y_OFFSET);
+    }
+
+    @Override
+    public PacketGroup newDestroyPackets() {
+        return new EntityDestroyNMSPacket(itemID, vehicleID);
+    }
+
+}

nms/v1_20_r3/src/main/java/me/filoghost/holographicdisplays/nms/v1_20_R3/VersionNMSManager.java

@@ -0,0 +1,123 @@
+/*
+ * Copyright (C) filoghost and contributors
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package me.filoghost.holographicdisplays.nms.v1_20_R3;
+
+import io.netty.channel.Channel;
+import io.netty.channel.ChannelHandler;
+import io.netty.channel.ChannelPipeline;
+import me.filoghost.fcommons.logging.ErrorCollector;
+import me.filoghost.fcommons.logging.Log;
+import me.filoghost.fcommons.reflection.ReflectField;
+import me.filoghost.holographicdisplays.nms.common.EntityID;
+import me.filoghost.holographicdisplays.nms.common.FallbackEntityIDGenerator;
+import me.filoghost.holographicdisplays.nms.common.NMSErrors;
+import me.filoghost.holographicdisplays.nms.common.NMSManager;
+import me.filoghost.holographicdisplays.nms.common.PacketListener;
+import me.filoghost.holographicdisplays.nms.common.entity.ClickableNMSPacketEntity;
+import me.filoghost.holographicdisplays.nms.common.entity.ItemNMSPacketEntity;
+import me.filoghost.holographicdisplays.nms.common.entity.TextNMSPacketEntity;
+import net.minecraft.network.NetworkManager;
+import net.minecraft.server.network.PlayerConnection;
+import net.minecraft.server.network.ServerCommonPacketListenerImpl;
+import net.minecraft.world.entity.Entity;
+import org.bukkit.craftbukkit.v1_20_R3.entity.CraftPlayer;
+import org.bukkit.entity.Player;
+
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Consumer;
+import java.util.function.Supplier;
+
+public class VersionNMSManager implements NMSManager {
+
+    private static final ReflectField<AtomicInteger> ENTITY_ID_COUNTER_FIELD = ReflectField.lookup(AtomicInteger.class, Entity.class, "d");
+    private static final ReflectField<NetworkManager> NETWORK_MANAGER_FIELD = ReflectField.lookup(NetworkManager.class, ServerCommonPacketListenerImpl.class, "c");
+    private final Supplier<Integer> entityIDGenerator;
+
+    public VersionNMSManager(ErrorCollector errorCollector) {
+        this.entityIDGenerator = getEntityIDGenerator(errorCollector);
+
+        // Force initialization of class to eventually throw exceptions early
+        DataWatcherKey.ENTITY_STATUS.getIndex();
+    }
+
+    private Supplier<Integer> getEntityIDGenerator(ErrorCollector errorCollector) {
+        try {
+            AtomicInteger nmsEntityIDCounter = ENTITY_ID_COUNTER_FIELD.getStatic();
+            return nmsEntityIDCounter::incrementAndGet;
+        } catch (ReflectiveOperationException e) {
+            errorCollector.add(e, NMSErrors.EXCEPTION_GETTING_ENTITY_ID_GENERATOR);
+            return new FallbackEntityIDGenerator();
+        }
+    }
+
+    private EntityID newEntityID() {
+        return new EntityID(entityIDGenerator);
+    }
+
+    @Override
+    public TextNMSPacketEntity newTextPacketEntity() {
+        return new VersionTextNMSPacketEntity(newEntityID());
+    }
+
+    @Override
+    public ItemNMSPacketEntity newItemPacketEntity() {
+        return new VersionItemNMSPacketEntity(newEntityID(), newEntityID());
+    }
+
+    @Override
+    public ClickableNMSPacketEntity newClickablePacketEntity() {
+        return new VersionClickableNMSPacketEntity(newEntityID());
+    }
+
+    @Override
+    public void injectPacketListener(Player player, PacketListener packetListener) {
+        modifyPipeline(player, (ChannelPipeline pipeline) -> {
+            ChannelHandler currentListener = pipeline.get(InboundPacketHandler.HANDLER_NAME);
+            if (currentListener != null) {
+                pipeline.remove(InboundPacketHandler.HANDLER_NAME);
+            }
+            pipeline.addBefore("packet_handler", InboundPacketHandler.HANDLER_NAME, new InboundPacketHandler(player, packetListener));
+        });
+    }
+
+    @Override
+    public void uninjectPacketListener(Player player) {
+        modifyPipeline(player, (ChannelPipeline pipeline) -> {
+            ChannelHandler currentListener = pipeline.get(InboundPacketHandler.HANDLER_NAME);
+            if (currentListener != null) {
+                pipeline.remove(InboundPacketHandler.HANDLER_NAME);
+            }
+        });
+    }
+
+    /*
+     * Modifying the pipeline in the main thread can cause deadlocks, delays and other concurrency issues,
+     * which can be avoided by using the event loop. Thanks to ProtocolLib for this insight.
+     */
+    private void modifyPipeline(Player player, Consumer<ChannelPipeline> pipelineModifierTask) {
+        PlayerConnection playerConnection = ((CraftPlayer) player).getHandle().c;
+        NetworkManager networkManager;
+        try {
+            networkManager = NETWORK_MANAGER_FIELD.get(playerConnection);
+        } catch (ReflectiveOperationException e) {
+            Log.warning(NMSErrors.EXCEPTION_MODIFYING_CHANNEL_PIPELINE, e);
+            return;
+        }
+        Channel channel = networkManager.n;
+
+        channel.eventLoop().execute(() -> {
+            if (!player.isOnline()) {
+                return;
+            }
+            try {
+                pipelineModifierTask.accept(channel.pipeline());
+            } catch (Exception e) {
+                Log.warning(NMSErrors.EXCEPTION_MODIFYING_CHANNEL_PIPELINE, e);
+            }
+        });
+    }
+
+}

nms/v1_20_r3/src/main/java/me/filoghost/holographicdisplays/nms/v1_20_R3/VersionNMSPacket.java

@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) filoghost and contributors
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package me.filoghost.holographicdisplays.nms.v1_20_R3;
+
+import me.filoghost.holographicdisplays.nms.common.PacketGroup;
+import net.minecraft.network.protocol.Packet;
+import org.bukkit.craftbukkit.v1_20_R3.entity.CraftPlayer;
+import org.bukkit.entity.Player;
+
+abstract class VersionNMSPacket implements PacketGroup {
+
+    @Override
+    public void sendTo(Player player) {
+        ((CraftPlayer) player).getHandle().c.b(getRawPacket());
+    }
+
+    abstract Packet<?> getRawPacket();
+
+}

nms/v1_20_r3/src/main/java/me/filoghost/holographicdisplays/nms/v1_20_R3/VersionTextNMSPacketEntity.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) filoghost and contributors
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package me.filoghost.holographicdisplays.nms.v1_20_R3;
+
+import me.filoghost.holographicdisplays.common.PositionCoordinates;
+import me.filoghost.holographicdisplays.nms.common.EntityID;
+import me.filoghost.holographicdisplays.nms.common.IndividualTextPacketGroup;
+import me.filoghost.holographicdisplays.nms.common.PacketGroup;
+import me.filoghost.holographicdisplays.nms.common.entity.TextNMSPacketEntity;
+
+class VersionTextNMSPacketEntity implements TextNMSPacketEntity {
+
+    private final EntityID armorStandID;
+
+    VersionTextNMSPacketEntity(EntityID armorStandID) {
+        this.armorStandID = armorStandID;
+    }
+
+    @Override
+    public PacketGroup newSpawnPackets(PositionCoordinates position, String text) {
+        return PacketGroup.of(
+                new EntitySpawnNMSPacket(armorStandID, EntityTypeID.ARMOR_STAND, position, ARMOR_STAND_Y_OFFSET),
+                EntityMetadataNMSPacket.builder(armorStandID)
+                        .setArmorStandMarker()
+                        .setCustomName(text)
+                        .build()
+        );
+    }
+
+    @Override
+    public IndividualTextPacketGroup newSpawnPackets(PositionCoordinates position) {
+        return IndividualTextPacketGroup.of(
+                new EntitySpawnNMSPacket(armorStandID, EntityTypeID.ARMOR_STAND, position, ARMOR_STAND_Y_OFFSET),
+                (String text) -> EntityMetadataNMSPacket.builder(armorStandID)
+                        .setArmorStandMarker()
+                        .setCustomName(text)
+                        .build()
+        );
+    }
+
+    @Override
+    public PacketGroup newChangePackets(String text) {
+        return EntityMetadataNMSPacket.builder(armorStandID)
+                .setCustomName(text)
+                .build();
+    }
+
+    @Override
+    public IndividualTextPacketGroup newChangePackets() {
+        return IndividualTextPacketGroup.of(
+                (String text) -> EntityMetadataNMSPacket.builder(armorStandID)
+                        .setCustomName(text)
+                        .build()
+        );
+    }
+
+    @Override
+    public PacketGroup newTeleportPackets(PositionCoordinates position) {
+        return new EntityTeleportNMSPacket(armorStandID, position, ARMOR_STAND_Y_OFFSET);
+    }
+
+    @Override
+    public PacketGroup newDestroyPackets() {
+        return new EntityDestroyNMSPacket(armorStandID);
+    }
+
+}

pom.xml

@@ -213,6 +213,12 @@
                 <version>${project.version}</version>
             </dependency>
 
+            <dependency>
+                <groupId>${project.groupId}</groupId>
+                <artifactId>holographicdisplays-nms-v1_20_r3</artifactId>
+                <version>${project.version}</version>
+            </dependency>
+
             <dependency>
                 <groupId>org.spigotmc</groupId>
                 <artifactId>spigot-api</artifactId>