scaling new baby mob entities down on older clients

common/src/main/java/com/viaversion/viabackwards/api/entities/EntityScaleData.java

@@ -0,0 +1,47 @@
+/*
+ * This file is part of ViaBackwards - https://github.com/ViaVersion/ViaBackwards
+ * Copyright (C) 2016-2026 ViaVersion and contributors
+ *
+ * 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/>.
+ */
+package com.viaversion.viabackwards.api.entities;
+
+
+import com.viaversion.viaversion.api.data.entity.StoredEntityData;
+
+/**
+ * Storage object used within {@link StoredEntityData} to track the scaling state of an entity.
+ * This ensures that scale updates are only sent when the calculated scale actually changes.
+ */
+public final class EntityScaleData {
+
+    private boolean isBaby;
+    private float scale = 1.0f;
+
+    public boolean isBaby() {
+        return isBaby;
+    }
+
+    public void setBaby(boolean baby) {
+        this.isBaby = baby;
+    }
+
+    public float scale() {
+        return scale;
+    }
+
+    public void setScale(float scale) {
+        this.scale = scale;
+    }
+}

common/src/main/java/com/viaversion/viabackwards/api/entities/EntityScaleHelper.java

@@ -0,0 +1,104 @@
+/*
+ * This file is part of ViaBackwards - https://github.com/ViaVersion/ViaBackwards
+ * Copyright (C) 2016-2026 ViaVersion and contributors
+ *
+ * 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/>.
+ */
+package com.viaversion.viabackwards.api.entities;
+
+
+import com.google.common.base.Preconditions;
+import com.viaversion.viaversion.api.data.FullMappings;
+import com.viaversion.viaversion.api.data.entity.StoredEntityData;
+import com.viaversion.viaversion.api.minecraft.entities.EntityType;
+import com.viaversion.viaversion.api.minecraft.entitydata.EntityData;
+import com.viaversion.viaversion.api.protocol.Protocol;
+import com.viaversion.viaversion.api.protocol.packet.ClientboundPacketType;
+import com.viaversion.viaversion.api.protocol.packet.PacketWrapper;
+import com.viaversion.viaversion.api.type.Types;
+import com.viaversion.viaversion.rewriter.EntityRewriter;
+import com.viaversion.viaversion.rewriter.entitydata.EntityDataHandlerEvent;
+
+/**
+ * A helper for injecting entity scaling on older clients.
+ * This helper listens for the baby entity data flag and sends an UPDATE_ATTRIBUTES packet
+ * to scale the entity, since older clients might not support the newer entity variants natively.
+ */
+public class EntityScaleHelper {
+
+    private final ClientboundPacketType updateAttributesPacket;
+    private final EntityRewriter<?, ?> rewriter;
+
+    /**
+     * Constructs a new entity scale helper.
+     *
+     * @param rewriter               entity rewriter
+     * @param updateAttributesPacket UPDATE_ATTRIBUTES packet of the mapped protocol
+     * @param <CM>                   mapped clientbound packet type
+     */
+    public <CM extends ClientboundPacketType, P extends Protocol<?, CM, ?, ?>> EntityScaleHelper(final EntityRewriter<?, P> rewriter, final CM updateAttributesPacket) {
+        this.rewriter = rewriter;
+        this.updateAttributesPacket = updateAttributesPacket;
+    }
+
+    /**
+     * Registers a scaling factor for a specific baby entity type.
+     *
+     * @param type            entity type that requires scaling when it is a baby
+     * @param babyScaleFactor multiplier to apply to the minecraft:scale attribute when it is a baby
+     * @param babyIndex       entity data index for the baby property in this specific protocol
+     */
+    public void addBabyScale(final EntityType type, final float babyScaleFactor, final int babyIndex) {
+        rewriter.filter().type(type).index(babyIndex).handler(((event, data) -> trackAndSend(event, data, babyScaleFactor)));
+    }
+
+    /**
+     * Checks the entity data, tracks the scale state and sends an UPDATE_ATTRIBUTES packet if needed.
+     */
+    public void trackAndSend(final EntityDataHandlerEvent event, final EntityData data, final float babyScaleFactor) {
+        if (event.trackedEntity() == null) {
+            return;
+        }
+
+        final StoredEntityData storedEntityData = event.trackedEntity().data();
+        EntityScaleData scaleData = storedEntityData.get(EntityScaleData.class);
+        if (scaleData == null) {
+            scaleData = new EntityScaleData();
+            storedEntityData.put(scaleData);
+        }
+
+        final boolean isBaby = data.value();
+        if (scaleData.isBaby() == isBaby) {
+            return;
+        }
+
+        scaleData.setBaby(isBaby);
+        scaleData.setScale(isBaby ? babyScaleFactor : 1.0f);
+
+        final FullMappings attributeMappings = rewriter.protocol().getMappingData().getAttributeMappings();
+        int attributeId = attributeMappings.mappedId("scale");
+        if (attributeId == -1) {
+            attributeId = attributeMappings.mappedId("generic.scale");
+            Preconditions.checkArgument(attributeId != -1);
+        }
+
+        final PacketWrapper attributesPacket = PacketWrapper.create(updateAttributesPacket, event.user());
+        attributesPacket.write(Types.VAR_INT, event.entityId());
+        attributesPacket.write(Types.VAR_INT, 1); // 1 attribute
+        attributesPacket.write(Types.VAR_INT, attributeId);
+        attributesPacket.write(Types.DOUBLE, (double) scaleData.scale());
+        attributesPacket.write(Types.VAR_INT, 0); // 0 modifiers
+        attributesPacket.send(rewriter.protocol().getClass());
+    }
+}

common/src/main/java/com/viaversion/viabackwards/protocol/v1_21_2to1_21/rewriter/EntityPacketRewriter1_21_2.java

@@ -23,6 +23,7 @@
 import com.viaversion.nbt.tag.ListTag;
 import com.viaversion.nbt.tag.Tag;
 import com.viaversion.viabackwards.ViaBackwards;
+import com.viaversion.viabackwards.api.entities.EntityScaleHelper;
 import com.viaversion.viabackwards.api.rewriters.EntityRewriter;
 import com.viaversion.viabackwards.protocol.v1_21_2to1_21.Protocol1_21_2To1_21;
 import com.viaversion.viabackwards.protocol.v1_21_2to1_21.storage.PlayerStorage;
@@ -64,6 +65,7 @@ public final class EntityPacketRewriter1_21_2 extends EntityRewriter<Clientbound
     private static final int REL_DELTA_Y = 6;
     private static final int REL_DELTA_Z = 7;
     private static final int REL_ROTATE_DELTA = 8;
+    private static final int WATER_CREATURE_BABY_INDEX = 16;
     private boolean warned = ViaBackwards.getConfig().suppressEmulationWarnings();
 
     public EntityPacketRewriter1_21_2(final Protocol1_21_2To1_21 protocol) {
@@ -643,9 +645,15 @@ protected void registerRewrites() {
 
         filter().type(EntityTypes1_21_2.ABSTRACT_BOAT).addIndex(11); // Boat type
         filter().type(EntityTypes1_21_2.SALMON).removeIndex(17); // Data type
-        filter().type(EntityTypes1_21_2.AGEABLE_WATER_CREATURE).removeIndex(16); // Baby
 
         filter().type(EntityTypes1_21_2.ABSTRACT_ARROW).removeIndex(10); // In ground
+
+        final EntityScaleHelper scaleHelper = new EntityScaleHelper(this, ClientboundPackets1_21.UPDATE_ATTRIBUTES);
+        scaleHelper.addBabyScale(EntityTypes1_21_2.SQUID, 0.5f, WATER_CREATURE_BABY_INDEX);
+        scaleHelper.addBabyScale(EntityTypes1_21_2.GLOW_SQUID, 0.5f, WATER_CREATURE_BABY_INDEX);
+        scaleHelper.addBabyScale(EntityTypes1_21_2.DOLPHIN, 0.65f, WATER_CREATURE_BABY_INDEX);
+
+        filter().type(EntityTypes1_21_2.AGEABLE_WATER_CREATURE).removeIndex(WATER_CREATURE_BABY_INDEX);
     }
 
     @Override

common/src/main/java/com/viaversion/viabackwards/protocol/v1_21_6to1_21_5/rewriter/EntityPacketRewriter1_21_6.java

@@ -17,6 +17,7 @@
  */
 package com.viaversion.viabackwards.protocol.v1_21_6to1_21_5.rewriter;
 
+import com.viaversion.viabackwards.api.entities.EntityScaleHelper;
 import com.viaversion.viabackwards.api.rewriters.EntityRewriter;
 import com.viaversion.viabackwards.protocol.v1_21_6to1_21_5.Protocol1_21_6To1_21_5;
 import com.viaversion.viaversion.api.minecraft.entities.EntityType;
@@ -98,6 +99,11 @@ protected void registerRewrites() {
         filter().type(EntityTypes1_21_6.HANGING_ENTITY).removeIndex(8); // Direction
         filter().type(EntityTypes1_21_6.HAPPY_GHAST).cancel(17); // Leash holder
         filter().type(EntityTypes1_21_6.HAPPY_GHAST).cancel(18); // Stays still
+
+        // Scale 0.2375 reduces the 4.0x4.0 Ghast hitbox to roughly 0.95x0.95 (approx 1x1) for the Ghastling
+        final EntityScaleHelper scaleHelper = new EntityScaleHelper(this, ClientboundPackets1_21_5.UPDATE_ATTRIBUTES);
+        scaleHelper.addBabyScale(EntityTypes1_21_6.HAPPY_GHAST, 0.2375f, 16);
+        filter().type(EntityTypes1_21_6.HAPPY_GHAST).cancel(16); // Charging for regular ghasts
     }
 
     @Override