RealityKit – Material's Alpha transparency

Is it possible to have alpha transparency with textures?

I have png file that contains 8 bit RGBA, but for some reason, the supposed-to-be-transparent parts are simply black.

I assign the material like this:

private func setupLightMeshes(_ scene: Entity) {
    let lightEntity = scene.findEntity(named: "LightWindow_Plane")!
    var lightMaterial = UnlitMaterial()
    
    lightMaterial.baseColor = try! MaterialColorParameter.texture(
    TextureResource.load(named: "light.png")) // this is 8bpc RGBA
    var modelComponent = lightEntity.components[ModelComponent] as! ModelComponent
    modelComponent = ModelComponent(mesh: modelComponent.mesh, materials: [lightMaterial])
    lightEntity.components.set(modelComponent)
}

iOS RealityKit 1.0

.tintColor is a multiplier for .baseColor

If you have a .png file with a premultiplied alpha (RGB*A). all you need to do is to additionally use a tintColor instance property with alpha equal to 0.9999.

material.tintColor = UIColor(white: 1.0, alpha: 0.9999)

Here's how it looks like in a real code:

fileprivate func material() -> UnlitMaterial {

    var material = UnlitMaterial()
    material.baseColor = try! .texture(.load(named: "transparent.png"))
    material.tintColor = UIColor(white: 1.0, alpha: 0.9999)
    return material
}

override func viewDidLoad() {
    super.viewDidLoad()
    
    let sphere: MeshResource = .generateSphere(radius: 0.5)

    let entity = ModelEntity(mesh: sphere,
                        materials: [material()])

    let anchor = AnchorEntity()
    anchor.orientation = simd_quatf(angle: .pi, axis: [0, 1, 0])

    anchor.addChild(entity)
    arView.scene.anchors.append(anchor)
}

Seems like a bug in RealityKit for iOS – why png transparency doesn't work as expected?!

iOS RealityKit 2.0

The same story about partially transparent textures is in RealityKit 2.0:

var material = SimpleMaterial()

material.color = try! .init(tint: .white.withAlphaComponent(0.9999),
                         texture: .init(.load(named: "semi.png", in: nil)))

tint parameter is a multiplier for texture as well.

RealityKit for visionOS

In visionOS app, to create a transparent material has become easier with OpacityComponent:

modelEntity.components[OpacityComponent.self] = .init(opacity: 0.25)