Trying to figure out how I create a SCNGeometry with polygon as primitiveType, My goal is to add polygon shaped node as a child of a sphere node, and make it look like MKPolygon for map kit, like in this example.
My current code is:
//Take an arbitrary array of vectors
let vertices: [SCNVector3] = [
SCNVector3Make(-0.1304485, 0.551937, 0.8236193),
SCNVector3Make(0.01393811, 0.601815, 0.7985139),
SCNVector3Make(0.2971005, 0.5591929, 0.7739732),
SCNVector3Make(0.4516893, 0.5150381, 0.7285002),
SCNVector3Make(0.4629132, 0.4383712, 0.7704169),
SCNVector3Make(0.1333823, 0.5224985, 0.8421428),
SCNVector3Make(-0.1684743, 0.4694716, 0.8667254)]
//Does polygon shape require indices?
let indices: [Int] = [0,1,2,3,4,5,6]
let vertexSource = SCNGeometrySource(vertices: vertices)
let indexData = Data(bytes: indices, count: indices.count * MemoryLayout<Int>.size)
//Note!!! I get compiler error if primitiveCount is greater than 0
let element = SCNGeometryElement(data: indexData, primitiveType: .polygon, primitiveCount: 0, bytesPerIndex: MemoryLayout<Int>.size)
let geometry = SCNGeometry(sources: [vertexSource], elements: [element])
let material = SCNMaterial()
material.diffuse.contents = UIColor.purple.withAlphaComponent(0.75)
material.isDoubleSided = true
geometry.firstMaterial = material
let node = SCNNode(geometry: geometry)
When using SCNGeometryElement like this I get an empty node.
You have two problems:
SceneKit (and Metal) only support 32 bit integers as indices (source). So the type of your indices array needs to be
[Int32]
.SceneKit needs two pieces of information for polygons: The number of points in the polygon and the index of the point in the vertex array. From Apple's documentation on
SCNGeometryPrimitiveTypePolygon
(which only exists in Objective-C):You need to change your index array to:
Then, set the
primitiveCount
to 1 (we have one polygon to draw) and change the size of the buffer: