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Creating a mesh programatically
Given an array of vertices, normals, texture coordinates, and a triangle index list, how do I create a mesh that that I can load into an ECS Entity?
Hi!
There are a couple of different pieces of this, so I will break them down in two parts.
Creating a custom SceneMesh
The SceneMesh is the actual object that represents the geometry that we are rendering. It is usually managed for you when interacting with the ECS but behind the scenes, we are creating SceneMeshes and SceneObjects in Systems.
If you just want to create the mesh, you can use SceneMesh.meshWithMaterials(). This let's you set the positions, normals, UVs, vertex colors, indices, material ranges, and SceneMaterials as arrays.
Alternatively, you can create a SceneMesh using our TriangleMesh API (which is used in our Media Player Sample: https://github.com/meta-quest/Meta-Spatial-SDK-Samples/blob/1931b9d04f2e4979f005316127c39e926e44a1fe/MediaPlayerSample/app/src/main/java/com/meta/spatial/samples/mediaplayersample/MediaPlayerSampleActivity.kt#L316). This has a very similar API with meshWithMaterials() but is a little more verbose.
Attaching the SceneMesh to ECS
Once we know how to create a SceneMesh, there are a number of ways to add it to our ECS.One of the more simple ways is to use mesh creators. These allow you to create your mesh on-demand when you add a Mesh component to your entity with a matching "mesh://..." URI. For example, in your case, you can register a mesh creator like this:// in the app's onCreate() registerMeshCreator("mesh://myCustomMesh") { SceneMesh.meshWithMaterials(...) } // later in your code, we create an instance of it val myEntity = Entity.create(Mesh(Uri.parse("mesh://myCustomMesh"))Alternatively, you can use the MeshManager.setMeshForEntityDirectly() although it is less recommended. Your code would look something like this:
systemManager .findSystem<MeshCreationSystem>() .meshManager .setMeshForEntityDirectly(myEntity, mySceneMesh)Hope this helps!
Hi!
There are a couple of different pieces of this, so I will break them down in two parts.
Creating a custom SceneMesh
The SceneMesh is the actual object that represents the geometry that we are rendering. It is usually managed for you when interacting with the ECS but behind the scenes, we are creating SceneMeshes and SceneObjects in Systems.
If you just want to create the mesh, you can use SceneMesh.meshWithMaterials(). This let's you set the positions, normals, UVs, vertex colors, indices, material ranges, and SceneMaterials as arrays.
Alternatively, you can create a SceneMesh using our TriangleMesh API (which is used in our Media Player Sample: https://github.com/meta-quest/Meta-Spatial-SDK-Samples/blob/1931b9d04f2e4979f005316127c39e926e44a1fe/MediaPlayerSample/app/src/main/java/com/meta/spatial/samples/mediaplayersample/MediaPlayerSampleActivity.kt#L316). This has a very similar API with meshWithMaterials() but is a little more verbose.
Attaching the SceneMesh to ECS
Once we know how to create a SceneMesh, there are a number of ways to add it to our ECS.
One of the more simple ways is to use mesh creators. These allow you to create your mesh on-demand when you add a Mesh component to your entity with a matching "mesh://..." URI. For example, in your case, you can register a mesh creator like this:
// in the app's onCreate()
registerMeshCreator("mesh://myCustomMesh") {
SceneMesh.meshWithMaterials(...)
}
// later in your code, we create an instance of it
val myEntity = Entity.create(Mesh(Uri.parse("mesh://myCustomMesh"))Alternatively, you can use the MeshManager.setMeshForEntityDirectly() although it is less recommended. Your code would look something like this:
systemManager
.findSystem<MeshCreationSystem>()
.meshManager
.setMeshForEntityDirectly(myEntity, mySceneMesh)Hope this helps!
The meshWithMaterials method also takes the following parameters:
colors: IntArray (is this 3 or 4 channels; what is the range of each channel)
materialRanges: IntArray (not sure how this is encoded? must be indexes for materials array?)
indices: IntArray : are these triangle indices or triangle-strip?
I also must admit I don't know how to create a simple SceneMaterial (e.g. an unlit yellow surface).