Fix: Unity Blend Shape Weight Not Replicating Across Network

Player toggles a smile. Locally the face changes. Other players see a still face. SkinnedMeshRenderer state isn’t replicated by Netcode by default.

The Symptom

Visible facial or morph changes don’t propagate to other clients. Position and animation replicate correctly; only blend shapes are static on remote views.

The Fix

using Unity.Netcode;
using UnityEngine;

public class FaceSync : NetworkBehaviour
{
    public SkinnedMeshRenderer face;
    public NetworkVariable<float> smile = new();
    private const int SmileIndex = 0;

    public override void OnNetworkSpawn()
    {
        smile.OnValueChanged += OnSmileChanged;
        OnSmileChanged(0, smile.Value);
    }

    private void OnSmileChanged(float oldV, float newV)
    {
        face.SetBlendShapeWeight(SmileIndex, newV);
    }

    [ServerRpc]
    public void SetSmileServerRpc(float v)
    {
        smile.Value = v;
    }
}

Owning client calls SetSmileServerRpc; server writes the NetworkVariable; all clients (including the owner) get OnValueChanged and apply locally.

Many Blend Shapes

For a face with 50+ shapes, NetworkList:

public NetworkList<float> weights = new();

public override void OnNetworkSpawn()
{
    weights.OnListChanged += ApplyAllWeights;
}

void ApplyAllWeights(NetworkListEvent<float> ev)
{
    for (int i = 0; i < weights.Count && i < face.sharedMesh.blendShapeCount; i++)
        face.SetBlendShapeWeight(i, weights[i]);
}

Bandwidth

For high-frequency face mocap, quantize floats to byte (0..255 = 0..100% weight) and send via custom message at 20Hz with linear interpolation locally. Saves a lot of bandwidth.

Verifying

Host + client. Owner changes smile. Remote view shows the change within one tick. If not, OnValueChanged isn’t firing on the remote — verify subscription order in OnNetworkSpawn.

“NetworkVariable for the value. OnValueChanged applies. Faces sync.”

Related Issues

For SkinnedMeshRenderer bounds, see SMR bounds. For Mecanim foot slide, see foot slide.

NetworkVariable. Apply in callback. Faces propagate.