Is it possible to project light on a transparent SCNFloor in ARKit?

Question

I want to put a SCNLight node and project a light to transparent SCNFloor? This will give the effect of light projection on real surface. Similar to shadowOnly lighting model that cast shadow. Is this possible?

Answer 1

Yes, you can do that by casting a white (or bleeded color) shadow instead of a black one. For that you have to use deferred shadows type that are rendered in a post-processing pass.

Consider, you must use two separate lights in your scene – first one for white shadows casting, and a second one for lighting objects that cast these white shadows. You're able to include and exclude objects from lighting scheme implementing categoryBitMask property.

// SETTING A SHADOW CATCHER
let plane = SCNPlane(width: 10, height: 10)
plane.firstMaterial?.isDoubleSided = true
plane.firstMaterial?.lightingModel = .shadowOnly
let planeNode = SCNNode(geometry: plane)
planeNode.eulerAngles.x = -.pi / 2
scene.rootNode.addChildNode(planeNode)

// SETTING A LIGHT
let lightNode = SCNNode()
lightNode.light = SCNLight()
lightNode.light?.type = .directional
lightNode.light?.intensity = 50
lightNode.light?.color = UIColor.black
lightNode.eulerAngles.x = -.pi / 2
scene.rootNode.addChildNode(lightNode)
    
// DEFERRED SHADOWS
lightNode.light?.castsShadow = true
lightNode.light?.shadowMode = .deferred          // important
lightNode.light?.forcesBackFaceCasters = true    // important
lightNode.light?.shadowRadius = 10
lightNode.light?.shadowColor = UIColor.white