Resolved How to query a RenderMeshArray?

Hi,

I'm using Unity 2022 URP and ECS 1.0.0-pre.65 with the corresponding Entities Graphics package.

In a ISystem I would like to query a RenderMeshArray

Using

Code (CSharp):

1. foreach (
2.     var (gameState, renderMeshArray)
3.     in SystemAPI.Query<RefRO<GameState>, RefRW<RenderMeshArray>>()
4. )

Gives the following error:
`The type 'Unity.Rendering.RenderMeshArray' must be convertible to 'Unity.Entities.IComponentData' in order to use it as parameter 'T' in the generic struct 'Unity.Entities.RefRW<T>'`

Where should I start?
Note that my goal is to create a system that modifies the Mesh of its entities at each update or so.

 

Yes, that's a good point. But I'd like to modify the mesh according to some algorithm. So I need access to the vertices/triangles/uvs in a System.

 

For your purpose you likely still need to use the MaterialMeshInfo component. Check out the code for it, it contains ids for the material and mesh of the entity, which point to either materials and meshes in the entity's rendermesharray, or to meshes registered directly to the BatchedRendererGroup.
If your meshes are stored in the RenderMeshArray, there's a method on it to get the correct mesh based on the MaterialMeshInfo:

Code (CSharp):

1.  /// <summary>
2.         /// Gets the mesh for given MaterialMeshInfo.
3.         /// </summary>
4.         /// <param name="materialMeshInfo">The MaterialMeshInfo to use.</param>
5.         /// <returns>Returns the associated Mesh instance or null if the mesh is runtime.</returns>
6.         public Mesh GetMesh(MaterialMeshInfo materialMeshInfo)

Note that the RenderMeshArray is a shared, managed component. so you can't access it in the exact same way as normal components.

 

So, I got it working, here is my take on this. I have a baked component called Meshable to identify the prefabs with the mesh I want to modify.

In an ISystem, in OnStartRunning:

Code (CSharp):

1.  
2. var meshableEntities = state.GetEntityQuery(typeof(Meshable)).ToEntityArray(AllocatorManager.TempJob);
3. var firstMeshableEntity = meshableEntities[0];
4. // Of course in the current ECS implementation, the RenderMeshArray is on a child entity
5. var linkedEntityGroup = state.EntityManager.GetBuffer<LinkedEntityGroup>(firstMeshableEntity);
6. var childEntity = linkedEntityGroup[1].Value;
7. var renderMeshArray = state.EntityManager.GetSharedComponentManaged<RenderMeshArray>(childEntity);
8.  

Then in the same function I operate on the RenderMeshArray. Here I'm creating 128 meshes:

Code (CSharp):

1.  
2. var n = 128;
3. var meshes = new Mesh[n];
4.  
5. for (var i = 0; i < n; i++)
6. {
7.     meshes[i] = new Mesh();
8. }
9.  
10. renderMeshArray.Meshes = meshes;
11. renderMeshArray.ResetHash128();
12.  

Still in OnStartRunning, I can now assign the newly created meshes to my entities:

Code (CSharp):

1.  
2. var index = 0;
3.            
4. foreach (var meshableEntity in meshableEntities)
5. {
6.     var meshableLinkedEntityGroup = state.EntityManager.GetBuffer<LinkedEntityGroup>(meshableEntity);
7.     // Retrieve the two linked child entities that ECS v1 create to render the prefab
8.     var meshableChildEntity1 = meshableLinkedEntityGroup[1].Value;
9.     var meshableChildEntity2 = meshableLinkedEntityGroup[2].Value;
10.     var materialMeshInfo1 = state.EntityManager.GetComponentData<MaterialMeshInfo>(meshableChildEntity1);
11.     var materialMeshInfo2 = state.EntityManager.GetComponentData<MaterialMeshInfo>(meshableChildEntity2);
12.     // Assign a unique mesh from the RenderMeshArray to each entity
13.     var staticIndex = MaterialMeshInfo.ArrayIndexToStaticIndex(index);
14.    
15.     materialMeshInfo1.Mesh = staticIndex;
16.     materialMeshInfo2.Mesh = staticIndex;
17.     // Mark as meshable child for easy query in OnUpdate
18.     state.EntityManager.AddComponent<MeshableChild>(meshableChildEntity1);
19.     state.EntityManager.AddComponent<MeshableChild>(meshableChildEntity2);
20.     state.EntityManager.SetComponentData(meshableChildEntity1, materialMeshInfo1);
21.     state.EntityManager.SetComponentData(meshableChildEntity2, materialMeshInfo2);
22.     state.EntityManager.SetSharedComponentManaged(meshableChildEntity1, renderMeshArray);
23.     state.EntityManager.SetSharedComponentManaged(meshableChildEntity2, renderMeshArray);
24.  
25.     // Omited: SetComponentData for renderBounds and worldRenderBounds
26.     index++;
27. }
28.  

Then in OnUpdate:

Code (CSharp):

1.  
2. var defaultRenderMeshArray = default(RenderMeshArray);
3. var renderMeshArray = defaultRenderMeshArray;
4.  
5. foreach (
6.     var (meshableChild, materialMeshInfo, entity)
7.     in SystemAPI.Query<RefRO<MeshableChild>, RefRO<MaterialMeshInfo>>().WithEntityAccess()
8. )
9. {
10.     if (renderMeshArray == defaultRenderMeshArray)
11.     {
12.         renderMeshArray = state.EntityManager.GetSharedComponentManaged<RenderMeshArray>(entity);
13.     }
14.  
15.     var mesh = renderMeshArray.GetMesh(materialMeshInfo.ValueRO);
16.  
17.     DoSomethingWithMesh(mesh);
18. }
19.  

And there you go: a way to modify meshes in a system.
Hope this helps, if you find a better approach please share, thanks.