wave5-post-transform-matrix-non-uniform-scale

PostTransformMatrix — Non-Uniform Scale

Intent

Apply non-uniform scale to entities using PostTransformMatrix, which is multiplied into LocalToWorld after the standard TRS computation.

Use When

• Non-uniform scale needed (e.g., (1, 2, 1) — taller but same width)
• Squash-and-stretch animation, terrain tile variations, procedurally scaled geometry

Avoid When

• Uniform scale is sufficient — use LocalTransform.Scale
• Non-uniform scale is baked and static — bake into mesh vertices or baked matrix directly

Senior Pattern

// In a custom LocalToWorld system (IJobChunk):
[BurstCompile]
public struct ApplyPostTransformJob : IJobChunk
{
    [ReadOnly]  public ComponentTypeHandle<LocalTransform> LocalTransformHandle;
    public ComponentTypeHandle<LocalToWorld> LocalToWorldHandle;
    // Optional — null when absent from chunk
    [ReadOnly]  public ComponentTypeHandle<PostTransformMatrix> PostTransformMatrixHandle;

    [BurstCompile]
    public void Execute(in ArchetypeChunk chunk, int unfilteredChunkIndex,
        bool useEnableMask, in v128 chunkEnabledMask)
    {
        var transforms = chunk.GetNativeArray(ref LocalTransformHandle);
        var localToWorlds = chunk.GetNativeArray(ref LocalToWorldHandle);

        // One null check per chunk, not per entity:
        bool hasPost = chunk.Has(ref PostTransformMatrixHandle);
        NativeArray<PostTransformMatrix> postArr = hasPost
            ? chunk.GetNativeArray(ref PostTransformMatrixHandle)
            : default;

        var enumerator = new ChunkEntityEnumerator(useEnableMask, chunkEnabledMask, chunk.Count);
        while (enumerator.NextEntityIndex(out var i))
        {
            float4x4 trs = transforms[i].ToMatrix();
            localToWorlds[i] = new LocalToWorld
            {
                Value = hasPost ? math.mul(trs, postArr[i].Value) : trs
            };
        }
    }
}

// Add PostTransformMatrix in Baker for authoring-time non-uniform scale:
public override void Bake(MyAuthoring authoring)
{
    var entity = GetEntity(TransformUsageFlags.Dynamic);
    AddComponent(entity, new PostTransformMatrix
    {
        Value = float4x4.Scale(authoring.NonUniformScale)
    });
}