How to assign a generated mesh to an entity and define its Physics Shape at runtime?

Hi!
Basically what's in the title.
I'm generating a mesh at runtime in a Component System (In its OnUpdate callback, because there's no way to create a mesh in a Job, right?), and I have the need to assign this mesh to a physics shape component (all the related components to have a working entity with physics) at runtime.
Until now I can't see a way to do it. Can someone point me in the right direction?
I'm using the following package versions:
- Unity Physics: 0.2.5
- Entities: 0.5.1-preview.11
And I'm currently using: 2019.3.0f3 as Unity version.
Thank you for any help!

 

I remember screenshotting this from someone else's code posted on this forum a while back:


This shows how to replace a collider (including its geometry) within a job. Maybe you can take inspiration from it. Not sure if there are additional complexities for mesh colliders

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Edit:
I suppose you can do something like this:

• myPhysicsCollider.Collider = MeshCollider.Create(verts, tris)

But I'm not sure about the performance of it if you're updating it every frame. Looks like we'd need a "MeshCollider.Update(verts, tris)" as well for better efficiency

 

Awesome!
The code was slightly similar to what you posted, here is the pseudo-code to assign a MeshCollider to an Entity:

Code (CSharp):

1.  
2. NativeArray<float3> meshVertices;
3. NativeArray<int3> meshTris;
4. using (meshTris = new NativeArray<int3>(generatedMesh.triangles.Length / 3, Allocator.Temp))
5. using (meshVertices = new NativeArray<float3>(generatedMesh.vertices.Length, Allocator.Temp))
6. {
7.     int index = 0;
8.     foreach (Vector3 v in generatedMesh.vertices)
9.           meshVertices[index++] = v;
10.  
11.      index = 0;
12.      for(int i = 0; i < generatedMesh.triangles.Length; i += 3)
13.           meshTris[index++] = new int3(generatedMesh.triangles[i], generatedMesh.triangles[i + 1], generatedMesh.triangles[i + 2]);
14.  
15.      BlobAssetReference<Unity.Physics.Collider> meshColliderReference = Unity.Physics.MeshCollider.Create(meshVertices, meshTris, Unity.Physics.CollisionFilter.Default, Unity.Physics.Material.Default);
16.      EntityManager.AddComponentData(entity, new Unity.Physics.PhysicsCollider() { Value = meshColliderReference });
17. }
18.  

I didn't even see the

Unity.Physics.MeshCollider.Create

static overloads, my bad..
Thank you again!

 

@ZzAtomiic - this is super helpful! Thanks so much.

Does anyone know if there is a more optimal way to create a Unity.Physics.MeshCollider from a Mesh?

For example, I saw this: https://gist.github.com/LotteMakesStuff/c2f9b764b15f74d14c00ceb4214356b4

Which uses a Vector3[] to NativeArray<float3> conversion function:

Code (CSharp):

1. unsafe NativeArray<float3> GetNativeVertexArrays(Vector3[] vertexArray)
2.     {
3.         // create a destination NativeArray to hold the vertices
4.         NativeArray<float3> verts = new NativeArray<float3>(vertexArray.Length, Allocator.Persistent,
5.             NativeArrayOptions.UninitializedMemory);
6.  
7.         // pin the mesh's vertex buffer in place...
8.         fixed (void* vertexBufferPointer = vertexArray)
9.         {
10.             // ...and use memcpy to copy the Vector3[] into a NativeArray<floar3> without casting. whould be fast!
11.             UnsafeUtility.MemCpy(NativeArrayUnsafeUtility.GetUnsafeBufferPointerWithoutChecks(verts),
12.                 vertexBufferPointer, vertexArray.Length * (long) UnsafeUtility.SizeOf<float3>());
13.         }
14.         // we only hve to fix the .net array in place, the NativeArray is allocated in the C++ side of the engine and
15.         // wont move arround unexpectedly. We have a pointer to it not a reference! thats basically what fixed does,
16.         // we create a scope where its 'safe' to get a pointer and directly manipulate the array
17.  
18.         return verts;
19.     }

The reason I ask is that I am hoping to generate thousands of irregular meshes, all with MeshColliders.

 

@roryo mind, that using tons of different meshes in SCD, will cause entities, to be scattered across different chunks.
Which may potentially lead, into loosing benefits of ECS.