CODEWITHSUNDEEP
iosswiftscenekitmetalarkit
Pop Flamingo
Pop Flamingo

Reputation: 2191

Model I/O mesh from custom data

I am trying to create a MDLMesh from my own custom data that I parsed from a file. The file only contains vertices positions and triangles indexes ; I extract them into two Swift Data objects, float3 format for vertices and uint32 format for indexes.

My problem is that my MDLMesh doesn't seem to work properly as I can't import it to SceneKit (the resulting SCNGeometry seems "empty") nor create normals from it (crashes).

Now here is the code for MDLMesh: 

 let mesh = MDLMesh()
        mesh.vertexBuffers = [MDLMeshBufferData(type: .vertex, data: vertexData)]
        mesh.vertexCount = floats.count/3
        let vertexDescriptor = MDLVertexDescriptor()
        let attribute = MDLVertexAttribute(name: MDLVertexAttributePosition, format: .float3, offset: 0, bufferIndex: 0)
        let layout = MDLVertexBufferLayout(stride: MemoryLayout<float3>.stride)
        vertexDescriptor.attributes = [attribute]
        vertexDescriptor.layouts = [layout]

Then I create a sub mesh (that describes the triangles) : 

let submesh = MDLSubmesh(indexBuffer:  MDLMeshBufferData(type: MDLMeshBufferType.index, data: indexData),
           indexCount: uint32Indexes.count-uint32Indexes.count/4,
           indexType: .uint32,
           geometryType: .triangles,
           material: nil)

mesh.submeshes = [submesh]

Do you see anything wrong ? Or could it just be that my data isn't correct ?
Thank you

NB: Note that indexCount and vertexCount are both right even tough their definition seems weird without more context :)

EDIT: When trying to make normals:

mesh.addNormals(withAttributeNamed: MDLVertexAttributeNormal, creaseThreshold: 0)

Here is the error I get:

2017-08-04 09:39:24.078436+0200 MyAppName[506:70657] * Terminating app due to uncaught exception 'NSRangeException', reason: '* -[__NSArrayM objectAtIndexedSubscript:]: index 1 beyond bounds [0 .. 0]'

Upvotes: 1

Views: 1535

Answers (2)

nightwill
nightwill

Reputation: 818

You should remove layout from VertexDescriptor:

these lines:

let layout = MDLVertexBufferLayout(stride: MemoryLayout<float3>.stride)
vertexDescriptor.layouts = [layout]

And add these lines at the end of setting VertexDescriptor:

vertexDescriptor.setPackedOffsets()
vertexDescriptor.setPackedStrides()

Upvotes: 1

elmon
elmon

Reputation: 21

Apple documentation on this method states: "Calling this method on a mesh that does not contain vertex position data raises an exception.", and I believe that it is exactly the issue here: your vertexData seems to have no elements in it.

Upvotes: 0

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