[1.17.1] Multipart Entity interaction

[TheOrangeInd]

Experimenting with multiparty entities, I ran into a problem. My part entity does not detect incoming damage. I was making my entities following the example of vanilla dragon, and I think I missed some important detail. I would be grateful for any hints.

 

So this is my Parent Entity class:

Spoiler

public class EntityTest extends Mob
{
    private final EntityTestPart[] subEntities;
    private final EntityTestPart core;

    protected EntityTest(EntityType<? extends Mob> type, Level level)
    {
        super(type, level);

        core = new EntityTestPart(this, "core", 1.0f, 1.0f);
        subEntities = new EntityTestPart[] {core};
    }

    public static AttributeSupplier.Builder createAttributes()
    {
        return Mob.createMobAttributes()
                .add(Attributes.MAX_HEALTH, 200.0D)
                .add(Attributes.KNOCKBACK_RESISTANCE, 0.95D);
    }

    @Override
    public void checkDespawn() { }

    protected void updateParts()
    {
        for (EntityTestPart part : subEntities)
            movePart(part, 0, 4.5f, 0);
    }

    protected void movePart(EntityTestPart part, double dX, double dY, double dZ)
    {
        Vec3 lastPos = new Vec3(part.getX(), part.getY(), part.getZ());

        part.setPos(this.getX() + dX, this.getY() + dY, this.getZ() + dZ);

        part.xo = lastPos.x;
        part.yo = lastPos.y;
        part.zo = lastPos.z;
        part.xOld = lastPos.x;
        part.yOld = lastPos.y;
        part.zOld = lastPos.z;
    }

    @Override
    public void aiStep()
    {
        super.aiStep();

        updateParts();
    }

    @Override
    public boolean isMultipartEntity() {
        return true;
    }

    @Override
    public net.minecraftforge.entity.PartEntity<?>[] getParts() { return this.subEntities; }

    public void recreateFromPacket(ClientboundAddMobPacket packet)
    {
        super.recreateFromPacket(packet);

        EntityTestPart[] parts = this.getSubEntities();
        for(int i = 0; i < parts.length; ++i)
            parts[i].setId(i + packet.getId());
    }

    public EntityTestPart[] getSubEntities() {
        return this.subEntities;
    }

    @Override
    public boolean isPickable() { return true; }

    @Override
    public Packet<?> getAddEntityPacket() {
        return new ClientboundAddMobPacket(this);
    }
}

 

and a Part Entity:

Spoiler

public class EntityTestPart extends PartEntity<EntityTest>
{
    public final String name;
    private final EntityDimensions size;

    public EntityTestPart(EntityTest parent, String name, float width, float height)
    {
        super(parent);
        this.size = EntityDimensions.scalable(width, height);
        refreshDimensions();
        this.name = name;
    }

    @Override
    public boolean hurt(DamageSource source, float amount)
    {
        System.out.println("HIT");
        return getParent().hurt(source, amount);
    }

    @Override
    public boolean is(Entity entity) {
        return this == entity || this.getParent() == entity;
    }

    @Override
    public EntityDimensions getDimensions(Pose pose) {
        return this.size;
    }

    @Override
    public boolean isPickable() {
        return true;
    }

    @Override
    public boolean shouldBeSaved() {
        return false;
    }

    @Override
    protected void defineSynchedData() { }

    @Override
    protected void readAdditionalSaveData(CompoundTag nbt) { }

    @Override
    protected void addAdditionalSaveData(CompoundTag nbt) { }
}

 

 

Edited August 1, 2021 by TheOrangeInd

[TheOrangeInd]

So, after researching how vanilla projectiles work, I found that when determining whether to hit the target, they request a list of entities using a method from the Level class (the method is called getEntities). So the fact is that in this method they directly check whether the entity is a vanilla Dragon and, if true, request its PartEntities. That is, this method cannot add custom PartEntities to the returned list as ordinary entities, since they do not exist in the world, but they are a logical continuation of the parent class. At the same time, the getEntities method does not ask the checked entity to check the isMultipartEntity (from IForgeEntity interface) and, accordingly, does not add entities returned by the getParts method to the list.

I still do not rule out the possibility that I misunderstand the principle of this system. But at the moment it seems to me that in the current version of Forge, the correct implementation of Multipart Entities in the way conceived by the API developers is not possible.
I will be glad if I'm wrong and someone will correct me.