MeshInstanceRendererSystem

protected override void OnUpdate()
{
    // We want to iterate over all unique MeshInstanceRenderer shared component data,
    // that are attached to any entities in the world
    EntityManager.GetAllUniqueSharedComponentDatas(m_CacheduniqueRendererTypes);

    for (int i = 0; i != m_CacheduniqueRendererTypes.Count; i++)
    {
        // For each unique MeshInstanceRenderer data, we want to get all entities with a TransformMatrix
        // SharedComponentData gurantees that all those entities are packed togehter in a chunk with linear memory layout.
        // As a result the copy of the matrices out is internally done via memcpy.
        var renderer = m_CacheduniqueRendererTypes[i];
        m_InstanceRendererGroup.SetFilter(renderer);
        var transforms = m_InstanceRendererGroup.GetComponentDataArray<TransformMatrix>();

        // Graphics.DrawMeshInstanced has a set of limitations that are not optimal for working with ECS.
        // Specifically:
        // * No way to push the matrices from a job
        // * no NativeArray API, currently uses Matrix4x4[]
        // As a result this code is not yet jobified.
        // We are planning to adjust this API to make it more efficient for this use case.

        // For now, we have to copy our data into Matrix4x4[] with a specific upper limit of how many instances we can render in one batch.
        // So we just have a for loop here, representing each Graphics.DrawMeshInstanced batch
        int beginIndex = 0;
        while (beginIndex < transforms.Length)
        {
            int length = math.min(m_MatricesArray.Length, transforms.Length - beginIndex);
            CopyMatrices(transforms, beginIndex, length, m_MatricesArray);
            Graphics.DrawMeshInstanced(renderer.mesh, 0, renderer.material, m_MatricesArray, length, null, renderer.castShadows, renderer.receiveShadows);

            beginIndex += length;
        }
    }

    m_CacheduniqueRendererTypes.Clear();
}