透明 SCNFloor 上的 SceneKit 阴影()

我有一个floor node，我需要在其上投射阴影directional light。该节点需要是透明的（用于AR环境）。 当我使用时这效果很好ARKit，但使用相同的设置SceneKit没有显示任何阴影或反射。我怎样才能投下阴影SceneKit像这样？ SceneKit 的问题是由我设置的事实引起的sceneView.backgroundColor = .clear- 但我需要这个应用程序中的这种行为。这可以通过某种方式避免吗？

演示此问题的示例代码（仅适用于设备，不适用于模拟器）：

@IBOutlet weak var sceneView: SCNView! {
    didSet {

        sceneView.scene = SCNScene()

        let cameraNode = SCNNode()
        cameraNode.camera = SCNCamera()
        sceneView.pointOfView = cameraNode

        let testNode = SCNNode(geometry: SCNBox(width: 1, height: 1, length: 1, chamferRadius: 0))
        testNode.position = SCNVector3(x: 0, y: 0, z: -5)
        sceneView.scene!.rootNode.addChildNode(testNode)

        let animation = SCNAction.rotateBy(x: 0, y: .pi, z: 0, duration: 3.0)
        testNode.runAction(SCNAction.repeatForever(animation), completionHandler: nil)

        let floor = SCNFloor()
        floor.firstMaterial!.colorBufferWriteMask = []
        floor.firstMaterial!.readsFromDepthBuffer = true
        floor.firstMaterial!.writesToDepthBuffer = true
        floor.firstMaterial!.lightingModel = .constant
        let floorNode = SCNNode(geometry: floor)
        floorNode.position = SCNVector3(x: 0, y: -2, z: 0)
        sceneView.scene!.rootNode.addChildNode(floorNode)

        let light = SCNLight()
        light.type = .directional
        light.shadowColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.5)
        light.color = UIColor.white
        light.castsShadow = true
        light.automaticallyAdjustsShadowProjection = true
        light.shadowMode = .deferred
        let sunLightNode = SCNNode()
        sunLightNode.position = SCNVector3(x: 1_000, y: 1_000, z: 0)
        sunLightNode.rotation = SCNVector4(x: 1, y: 0, z: 0, w: .pi * 1.5)
        sunLightNode.light = light
        sceneView.scene!.rootNode.addChildNode(sunLightNode)

        let omniLightNode: SCNNode = {
            let omniLightNode = SCNNode()
            let light: SCNLight = {
                let light = SCNLight()
                light.type = .omni
                return light
            }()
            omniLightNode.light = light
            return omniLightNode
        }()
        sceneView.scene!.rootNode.addChildNode(omniLightNode)
    }
}

override func viewDidLoad() {
    super.viewDidLoad()
    let tapGR = UITapGestureRecognizer(target: self, action: #selector(toggleTransparent))
    view.addGestureRecognizer(tapGR)
}

@objc func toggleTransparent() {
    transparent = !transparent
}

var transparent = false {
    didSet {
        sceneView.backgroundColor = transparent ? .clear : .white
    }
}

以下是 macOS 的相同示例，构建在 SceneKit 游戏项目之上：

import SceneKit
import QuartzCore

class GameViewController: NSViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // create a new scene
        let scene = SCNScene(named: "art.scnassets/ship.scn")!

        // create and add a camera to the scene
        let cameraNode = SCNNode()
        cameraNode.camera = SCNCamera()
        scene.rootNode.addChildNode(cameraNode)

        // place the camera
        cameraNode.position = SCNVector3(x: 0, y: 0, z: 15)

        let testNode = SCNNode(geometry: SCNBox(width: 1, height: 1, length: 1, chamferRadius: 0))
        testNode.position = SCNVector3(x: 0, y: 0, z: -5)
        scene.rootNode.addChildNode(testNode)

        let animation = SCNAction.rotateBy(x: 0, y: .pi, z: 0, duration: 3.0)
        testNode.runAction(SCNAction.repeatForever(animation), completionHandler: nil)

        let floor = SCNFloor()
        floor.firstMaterial!.colorBufferWriteMask = []
        floor.firstMaterial!.readsFromDepthBuffer = true
        floor.firstMaterial!.writesToDepthBuffer = true
        floor.firstMaterial!.lightingModel = .constant
        let floorNode = SCNNode(geometry: floor)
        floorNode.position = SCNVector3(x: 0, y: -2, z: 0)
        scene.rootNode.addChildNode(floorNode)

        let light = SCNLight()
        light.type = .directional
        light.shadowColor = NSColor(red: 0, green: 0, blue: 0, alpha: 0.5)
        light.color = NSColor.white
        light.castsShadow = true
        light.automaticallyAdjustsShadowProjection = true
        light.shadowMode = .deferred
        let sunLightNode = SCNNode()
        sunLightNode.position = SCNVector3(x: 1_000, y: 1_000, z: 0)
        sunLightNode.rotation = SCNVector4(x: 1, y: 0, z: 0, w: .pi * 1.5)
        sunLightNode.light = light
        scene.rootNode.addChildNode(sunLightNode)

        let omniLightNode: SCNNode = {
            let omniLightNode = SCNNode()
            let light: SCNLight = {
                let light = SCNLight()
                light.type = .omni
                return light
            }()
            omniLightNode.light = light
            return omniLightNode
        }()
        scene.rootNode.addChildNode(omniLightNode)

        // retrieve the SCNView
        let scnView = self.view as! SCNView

        // set the scene to the view
        scnView.scene = scene

        // allows the user to manipulate the camera
        scnView.allowsCameraControl = true

        // configure the view
        scnView.backgroundColor = .clear
//        scnView.backgroundColor = .white // shadow works in this mode, but I need it to be clear
    }
}

示例项目：

MacOS: https://www.dropbox.com/s/1o50mbgzg4gc0fg/Test_macOS.zip?dl=1

iOS: https://www.dropbox.com/s/fk71oay1sopc1vp/Test.zip?dl=1

在 macOS 中，您可以更改 ViewController 最后一行的背景颜色 - 我需要它清晰，这样我就可以在其下显示相机预览。

在下面的图片中，您可以看到 sceneView.backgroundColor 为白色时的样子，而下面的图片为透明。清晰版本没有阴影。

获得透明阴影有两个步骤：

First：您需要将其连接为node to the scene，不作为geometry type.

let floor = SCNNode()
floor.geometry = SCNFloor()
floor.geometry?.firstMaterial!.colorBufferWriteMask = []
floor.geometry?.firstMaterial!.readsFromDepthBuffer = true
floor.geometry?.firstMaterial!.writesToDepthBuffer = true
floor.geometry?.firstMaterial!.lightingModel = .constant
scene.rootNode.addChildNode(floor)

Shadow on invisible SCNFloor():

Shadow on visible SCNPlane() and our camera is under SCNFloor():

为了得到一个transparent shadow你需要设置一个shadow color，不是object's transparency itself.

Second : A shadow color对于 macOS 必须这样设置：

lightNode.light!.shadowColor = NSColor(calibratedRed: 0,
                                               green: 0, 
                                                blue: 0, 
                                               alpha: 0.5)

...对于 iOS 来说，它看起来像这样：

lightNode.light!.shadowColor = UIColor(white: 0, alpha: 0.5)

这里的 Alpha 分量（alpha: 0.5) is an opacity阴影和 RGB 分量（white: 0) 是阴影的黑色。

P.S.

sceneView.backgroundColor之间切换.clear颜色和.white colour.

在这种特殊情况下，我无法捕捉到强大的阴影sceneView.backgroundColor = .clear，因为你需要在之间切换RGBA=1,1,1,1 (白色模式：白色，alpha=1) 和RGBA=0,0,0,0 (清除模式：黑色，alpha=0）。

为了看到背景上的半透明阴影，组件应该是RGB=1,1,1 and A=0.5，但由于 SceneKit 的内部合成机制，这些值会使图像变白。但是当我设置RGB=1,1,1 and A=0.02影子非常微弱。

目前这是一个可以忍受的解决方法（在“解决方案”部分中查找下面的解决方案):

@objc func toggleTransparent() {
    transparent = !transparent
}  
var transparent = false {
    didSet {
        // this shadow is very FEEBLE and it's whitening BG image a little bit
        sceneView.backgroundColor = 
                        transparent ? UIColor(white: 1, alpha: 0.02) : .white
    }
}

let light = SCNLight()
light.type = .directional

if transparent == false {
    light.shadowColor = UIColor(white: 0, alpha: 0.9)
}

如果我设置light.shadowColor = UIColor(white: 0, alpha: 1)我去拿满意的影子在 BG 图像上但是纯黑色阴影在白色。

SOLUTION:

您应该抓取 3D 对象的渲染，以使用其有用的 Alpha 通道预乘 RGBA 图像。之后就可以复合了rgba image of cube and its shadow over image of nature使用经典的OVER在另一个View中进行合成操作。

这是一个公式OVER手术 ：

(RGB1 * A1) + (RGB2 * (1 – A1))