Lab 101 – Exploring Extrusion Methods
We can use linear, tracePositions, and traceTransforms to extrude meshes.
Overview
We recently took a look at extruding 3D meshes from paths. There are number of ShapeExtrusionOptions we can customize. This lab takes a quick look at extrusionMethod. There are three options.
linear: simplify provide a depth value in meterstracePositions: this will create segments for each position in an arraytraceTransforms: this will create segments for each transform matrix in an array
When can use tracePositions when we need to extrude a uniform shape along a path of positions. We can do something similar with traceTransforms, but we can also scale and rotate each segment connection, resulting in more complex shapes.
This lab uses two helper functions to generate traces along a slight arc.
var extrusionOptions = MeshResource.ShapeExtrusionOptions()
switch example {
case .linear:
extrusionOptions.extrusionMethod = .linear(depth: 0.05) // in meters
case .tracePositions:
extrusionOptions.extrusionMethod = .tracePositions(
arcTracePositions(count: 12)
)
case .traceTransforms:
extrusionOptions.extrusionMethod = .traceTransforms(
arcTraceMatrices(count: 24, startScale: .one, endScale: [2, 2, 2])
)
}Video Demo
Lab Code
struct Lab101: View {
private enum ExtrusionExample: String, CaseIterable, Identifiable {
case linear = "Linear"
case tracePositions = "Trace Positions"
case traceTransforms = "Trace Transforms"
var id: String { rawValue }
}
@State private var example: ExtrusionExample = .tracePositions
@State private var subject: ModelEntity?
@State private var appliedExample: ExtrusionExample?
var body: some View {
RealityView { content in
// Create and add the subject once.
let entity = ModelEntity()
subject = entity
content.add(entity)
// Initial build.
let built = await buildSubject(example: example)
if let model = built.model {
entity.model = model
}
appliedExample = example
spinSubject(entity: entity)
}
.onChange(of: example) { _, newValue in
guard let subject else { return }
guard appliedExample != newValue else { return }
Task { @MainActor in
let built = await buildSubject(example: newValue)
if let model = built.model {
subject.model = model
}
appliedExample = newValue
}
}
.toolbar {
ToolbarItem(placement: .bottomOrnament) {
Picker("Extrusion", selection: $example) {
ForEach(ExtrusionExample.allCases) { item in
Text(item.rawValue).tag(item)
}
}
.pickerStyle(.menu)
}
}
.realityViewLayoutBehavior(.centered)
}
@MainActor
private func buildSubject(example: ExtrusionExample) async -> ModelEntity {
// Materials
let mat1 = SimpleMaterial(color: .stepGreen, roughness: 0.2, isMetallic: false)
let mat2 = SimpleMaterial(color: .stepRed, roughness: 0.2, isMetallic: false)
let mat3 = SimpleMaterial(color: .stepBlue, roughness: 0.2, isMetallic: false)
let mat4 = SimpleMaterial(color: .stepBackgroundPrimary, roughness: 0.2, isMetallic: false)
// Extrusion options
var extrusionOptions = MeshResource.ShapeExtrusionOptions()
switch example {
case .linear:
extrusionOptions.extrusionMethod = .linear(depth: 0.05) // in meters
case .tracePositions:
extrusionOptions.extrusionMethod = .tracePositions(
arcTracePositions(count: 12)
)
case .traceTransforms:
extrusionOptions.extrusionMethod = .traceTransforms(
arcTraceMatrices(count: 24, startScale: .one, endScale: [2, 2, 2])
)
}
extrusionOptions.chamferRadius = 0.01
extrusionOptions.materialAssignment = .init(front: 0, back: 1, extrusion: 2, frontChamfer: 3, backChamfer: 3)
// Generate mesh
let mesh = try! await MeshResource(extruding: simplePath(), extrusionOptions: extrusionOptions)
// Build and return a new entity
return ModelEntity(mesh: mesh, materials: [mat1, mat2, mat3, mat4])
}
func arcTracePositions(
count n: Int,
radius: Float = 0.35,
height: Float = 0.05,
z: Float = 0
) -> [SIMD3<Float>] {
guard n >= 2 else { return [] }
let startX: Float = -0.25
let endX: Float = 0.25
return (0..<n).map { i in
let t = Float(i) / Float(n - 1) // 0 → 1
let x = simd_mix(startX, endX, t)
// Smooth arc using sine (peaks at center)
let y = sin(t * .pi) * height
return SIMD3<Float>(x, y, z)
}
}
func arcTraceMatrices(
count n: Int,
height: Float = 0.05,
x: Float = 0,
startZ: Float = -0.25,
endZ: Float = 0.25,
startScale: SIMD3<Float> = .one,
endScale: SIMD3<Float> = SIMD3<Float>(repeating: 1.12)
) -> [simd_float4x4] {
guard n >= 2 else { return [] }
return (0..<n).map { i in
let t = Float(i) / Float(n - 1) // 0 → 1
let z = simd_mix(startZ, endZ, t)
// Smooth arc using sine (peaks at center)
let y = sin(t * .pi) * height
let translation = SIMD3<Float>(x, y, z)
let scale = simd_mix(startScale, endScale, SIMD3<Float>(repeating: t))
let transform = Transform(
scale: scale,
rotation: simd_quatf(angle: 0, axis: SIMD3<Float>(0, 1, 0)),
translation: translation
)
return transform.matrix
}
}
// Just a helper function to create a Path
func simplePath() -> Path {
let points = 5
let outerRadius: CGFloat = 0.12
let innerRadius: CGFloat = 0.05
let center = CGPoint(x: 0, y: 0)
var path = Path()
let angleStep = .pi * 2 / CGFloat(points * 2)
for i in 0..<(points * 2) {
let radius = (i % 2 == 0) ? outerRadius : innerRadius
let angle = CGFloat(i) * angleStep - .pi / 2
let point = CGPoint(
x: center.x + cos(angle) * radius,
y: center.y + sin(angle) * radius
)
if i == 0 {
path.move(to: point)
} else {
path.addLine(to: point)
}
}
path.closeSubpath()
return path
}
// A helper function to spin the subject to showcase the extrusion
func spinSubject(entity: Entity) {
Task {
let action = SpinAction(revolutions: 1,
localAxis: [-0.25, 1, 0.25],
timingFunction: .easeInOut,
isAdditive: false)
let animation = try AnimationResource.makeActionAnimation(for: action,
duration: 3,
bindTarget: .transform,
repeatMode: .autoReverse)
entity.playAnimation(animation)
}
}
}Support our work so we can continue to bring you new examples and articles.
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