How to dynamically show or hide meshes from a Burstable ForEach job using Hybrid Renderer V2 in unity 2020?

Question

I have a specific way of generating meshes and structuring my scene that makes occlusion culling very straight forward and optimal. Now all I need is to know how to actually show or hide a mesh efficiently using the ECS hybrid renderer. I considered changing the layer to a hidden layer in the RenderMesh component but the RenderMesh component is an ISharedComponentData and so does not support jobification or burst. I saw the Unity BatchRendererGroup API and it looked promising with its OnPerformCulling callback but I don't know if it is possible to hook into the HybridRenderSystem's internal BatchRenderGroup. I also saw the DisableRendering IComponentData tag that I guess disables an entities rendering. However, again, this can only be done from the main thread. I can write my own solution to render meshes using Graphics.DrawMesh or something like it, but I would prefer to integrate it natively with HybridRenderer in order to also cull meshes that are not related to my procedural meshes.

Is any of this possible? What is the intended use?

Answer 1

The answer is that you can't and you shouldn't! Unity Hybrid rendering gets its speed by laying out data in sequence. If there was a boolean for each mesh that allowed you to show or hide the mesh Unity would still have to evaluate it which I guess is not in the their design philosophy. This whole design philosophy in general did not work out for me as I found out.

My world is made up of chunks of procedurally generated terrain meshes (think minecraft but better ;)) The problem with this is that each chunk has its own RenderMesh with a unique mesh... meaning that each chunk gets its own... chunk... in memory xD. Which, as appropriate as that sounds, is extremely inefficient. I decided to abandon Hybrid ECS all together and use good old game objects. With this change alone I saw a performance boost of 4x (going from 200 to 800fps). I just used the MeshRenderer.enabled property in order to efficiently enable and disable rendering. To jobify this I simply stored an array of the mesh bounds and a boolean for if it is visibile or not. This array I could then evaluate in a job and spit back out an index list of all the chunks that needed their visibility changed. This leaves only setting a few boolean values for the main thread which is not very expensive at all... It is not the ECS friendly solution I was looking for but from the looks of it, ECS was not exactly my friend here. Having unique meshes for each section of my world was clearly not the intended use case of Hybrid ECS.

Answer 2

I'm not sure it's the best option but you can maybe try parallel command buffer:

var ecb = new EntityCommandBuffer( Allocator.TempJob );
var cmd = ecb.AsParallelWriter();

/* job 1 executes with burst & cmd adds/removes Disabled or DisableRendering tags */

// (main thread) job 2 executes produced commands:
Job
    .WithName("playback_commands")
    .WithCode( () =>
    {
        ecb.Playback( EntityManager );
        ecb.Dispose();
    }
    ).WithoutBurst().Run();

Answer 3

There is another way of hiding/showing entities. But it requires you to group adjacent entities in chunks spatially (you're probably doing that already). Then you will be occluding not specific entities one by one but entire chunks of them (sectors of space). It's possible thanks to fabulous powers of:

chunk component data

var queryEnabled = EntityManager.CreateEntityQuery(
        ComponentType.ReadOnly<RenderMesh>()
    ,   ComponentType.Exclude<Disabled>()
);

queryEnabled.SetSharedComponentFilter( new SharedSector {
        Value = new int3{ x=4 , y=1 , z=7 }
} );

EntityManager.AddChunkComponentData( queryEnabled , default(Disabled) );
// EntityManager.RemoveChunkComponentData<Disabled>( queryDisabled );

public struct SharedSector : ISharedComponentData
{
    public int3 Value;
}