blob-asset-deduplication

Blob Asset Deduplication

Intent

Avoid creating duplicate blob assets for identical source data by checking BlobAssetStore before building, using a stable hash as the deduplication key.

Use When

Multiple entities share the same source asset (same mesh, same config file, same ScriptableObject), and creating a separate blob per entity would waste memory. Also when incremental rebaking must avoid rebuilding blobs that haven't changed.

Avoid When

Every entity has unique blob content — deduplication adds overhead with no benefit. Avoid using GetHashCode() for the stable hash — it is not deterministic across domain reloads.

Senior Pattern

• Compute a stable hash from the source asset: AssetDatabase.GetAssetDependencyHash(path) for Unity assets; custom deterministic hash for procedural data.
• In Baker: AddBlobAsset(ref blobRef, out _) performs automatic per-Baker deduplication — identical blobs from the same Baker context are merged.
• For cross-Baker deduplication (baking system): access BlobAssetStore via state.World.GetExistingSystemManaged<BakingSystem>().BlobAssetStore.
• blobAssetStore.TryGet<T>(hash, out var existing) — returns true if an identical blob was already created this bake cycle.
• If TryGet returns false: create the blob, call blobAssetStore.TryAdd(hash, ref blobRef).
• Track processed hashes locally (NativeParallelHashMap) to avoid redundant work within one baking system pass.

Code Template

[WorldSystemFilter(WorldSystemFilterFlags.BakingSystem)]
public partial struct MeshBlobBakingSystem : ISystem
{
    private NativeParallelHashMap<Hash128, BlobAssetReference<MeshBlobData>> m_Cache;

    public void OnCreate(ref SystemState state)
    {
        m_Cache = new NativeParallelHashMap<Hash128, BlobAssetReference<MeshBlobData>>(
            64, Allocator.Persistent);
    }

    public void OnDestroy(ref SystemState state) => m_Cache.Dispose();

    public void OnUpdate(ref SystemState state)
    {
        var blobStore = state.World
            .GetExistingSystemManaged<BakingSystem>().BlobAssetStore;

        foreach (var (rawMesh, entity) in
            SystemAPI.Query<RefRO<RawMeshData>>()
                .WithOptions(EntityQueryOptions.IncludePrefab |
                             EntityQueryOptions.IncludeDisabledEntities)
                .WithEntityAccess())
        {
            var hash = rawMesh.ValueRO.SourceHash;

            if (!m_Cache.TryGetValue(hash, out var blobRef))
            {
                if (!blobStore.TryGet(hash, out blobRef))
                {
                    blobRef = BuildMeshBlob(rawMesh.ValueRO);
                    blobStore.TryAdd(hash, ref blobRef);
                }
                m_Cache[hash] = blobRef;
            }

            state.EntityManager.AddComponentData(entity,
                new MeshBlobComponent { Blob = blobRef });
        }
    }
}