Orienting a directional light towards the camera in ARKit

Question

I'm trying to place a directional light oriented towards the camera to simulate a sun (as in the user points the camera towards the sun, and presses a button to place the directional light source).

So far, I have tried to take the quaternion conjugate of the camera point of view and assigning it to the lights rotation. However, this method does not seem to work and the resulting position of the light seems fairly random. Any suggestion on how this usually would be handled is greatly appreciated. This is my code:

 //Disable the default lightning updates
 sceneView.autoenablesDefaultLighting = false
 sceneView.automaticallyUpdatesLighting = false

 var sunLight = SCNLight()
 sunLight.intensity = 1000
 sunLight.type = .directional
 sunLight.color = UIColor.white
 sunLight.castsShadow = true
 sunLight.shadowMode = .forward
 sunLight.automaticallyAdjustsShadowProjection = true

 var sunNode = SCNNode()
 sunNode.light = sunLight
 sunNode.castsShadow = true

 guard let cameraNode = self.sceneView.pointOfView else { return }
 let q = cameraNode.orientation
 let qConjugate = SCNVector4(x: -q.x, y: -q.y, z: -q.z, w: q.w)
 sunNode.rotation = qConjugate
 sceneView.scene.rootNode.addChildNode(sunNode)

By placing a sphere I can see from which direction the light is coming from:

 let sphere = SCNSphere(radius: 0.3)
 sphere.firstMaterial?.diffuse.contents = UIColor.green.withAlphaComponent(1)
 let sphereNode = SCNNode(geometry: sphere)
 sphereNode.position = SCNVector3(0,0,0)
 sceneView.scene.rootNode.addChildNode(sphereNode)

Andy Jazz Andy Jazz · Accepted Answer · 2019-04-28T10:49:45

This is the case when you should use a SCNConstraint. A constraint that orients a node to always point toward the current camera is SCNBillboardConstraint.

An SCNBillboardConstraint object automatically adjusts a node’s orientation so that its local z-axis always points toward the pointOfView node currently being used to render the scene. For example, you can use a billboard constraint to efficiently render parts of a scene using two-dimensional sprite images instead of three-dimensional geometry – by mapping sprites onto planes affected by a billboard constraint, the sprites maintain their orientation with respect to the viewer.

let sunNode = SCNNode()
sunNode.light = SCNLight()
sunNode.light!.type = .directional
sunNode.light!.color = UIColor.yellow
sunNode.light!.intensity = 5000

let sunConstraint = SCNBillboardConstraint()
sunNode.constraints = [SCNBillboardConstraint()]
sunNode.constraints?.append(sunConstraint)

Orienting a directional light towards the camera in ARKit

1 Answers