我正在使用iOS上的SceneKit开发一些代码，在我的代码中，我想确定全局z平面上z为0.0时的x和y坐标，并且x和y是从一个触摸手势中确定的。我的设置如下：
override func viewDidLoad() {
super.viewDidLoad()
// create a new scene
let scene = SCNScene()
// create and add a camera to the scene
let cameraNode = SCNNode()
let camera = SCNCamera()
cameraNode.camera = camera
scene.rootNode.addChildNode(cameraNode)
// place the camera
cameraNode.position = SCNVector3(x: 0, y: 0, z: 15)
// create and add an ambient light to the scene
let ambientLightNode = SCNNode()
ambientLightNode.light = SCNLight()
ambientLightNode.light.type = SCNLightTypeAmbient
ambientLightNode.light.color = UIColor.darkGrayColor()
scene.rootNode.addChildNode(ambientLightNode)
let triangleNode = SCNNode()
triangleNode.geometry = defineTriangle();
scene.rootNode.addChildNode(triangleNode)
// retrieve the SCNView
let scnView = self.view as SCNView
// set the scene to the view
scnView.scene = scene
// configure the view
scnView.backgroundColor = UIColor.blackColor()
// add a tap gesture recognizer
let tapGesture = UITapGestureRecognizer(target: self, action: "handleTap:")
let gestureRecognizers = NSMutableArray()
gestureRecognizers.addObject(tapGesture)
scnView.gestureRecognizers = gestureRecognizers
}
func handleTap(gestureRecognize: UIGestureRecognizer) {
// retrieve the SCNView
let scnView = self.view as SCNView
// check what nodes are tapped
let p = gestureRecognize.locationInView(scnView)
// get the camera
var camera = scnView.pointOfView.camera
// screenZ is percentage between z near and far
var screenZ = Float((15.0 - camera.zNear) / (camera.zFar - camera.zNear))
var scenePoint = scnView.unprojectPoint(SCNVector3Make(Float(p.x), Float(p.y), screenZ))
println("tapPoint: (\(p.x), \(p.y)) scenePoint: (\(scenePoint.x), \(scenePoint.y), \(scenePoint.z))")
}
func defineTriangle() -> SCNGeometry {
// Vertices
var vertices:[SCNVector3] = [
SCNVector3Make(-2.0, -2.0, 0.0),
SCNVector3Make(2.0, -2.0, 0.0),
SCNVector3Make(0.0, 2.0, 0.0)
]
let vertexData = NSData(bytes: vertices, length: vertices.count * sizeof(SCNVector3))
var vertexSource = SCNGeometrySource(data: vertexData,
semantic: SCNGeometrySourceSemanticVertex,
vectorCount: vertices.count,
floatComponents: true,
componentsPerVector: 3,
bytesPerComponent: sizeof(Float),
dataOffset: 0,
dataStride: sizeof(SCNVector3))
// Normals
var normals:[SCNVector3] = [
SCNVector3Make(0.0, 0.0, 1.0),
SCNVector3Make(0.0, 0.0, 1.0),
SCNVector3Make(0.0, 0.0, 1.0)
]
let normalData = NSData(bytes: normals, length: normals.count * sizeof(SCNVector3))
var normalSource = SCNGeometrySource(data: normalData,
semantic: SCNGeometrySourceSemanticNormal,
vectorCount: normals.count,
floatComponents: true,
componentsPerVector: 3,
bytesPerComponent: sizeof(Float),
dataOffset: 0,
dataStride: sizeof(SCNVector3))
// Indexes
var indices:[CInt] = [0, 1, 2]
var indexData = NSData(bytes: indices, length: sizeof(CInt) * indices.count)
var indexElement = SCNGeometryElement(
data: indexData,
primitiveType: .Triangles,
primitiveCount: 1,
bytesPerIndex: sizeof(CInt)
)
var geo = SCNGeometry(sources: [vertexSource, normalSource], elements: [indexElement])
// material
var material = SCNMaterial()
material.diffuse.contents = UIColor.redColor()
material.doubleSided = true
material.shininess = 1.0;
geo.materials = [material];
return geo
}
正如你所看到的，我有一个三角形，高度为4个单位，宽度为4个单位，位于z平面上（z = 0），中心点为x，y坐标（0.0, 0.0）。相机是默认SCNCamera，面向负z方向，我将其放置在（0、0、15）处。 zNear和zFar的默认值分别为1.0和100.0。在我的handleTap方法中，我获取点击的x和y屏幕坐标，并尝试找到z = 0.0时的x和y全局场景坐标。我使用unprojectPoint进行调用。
unprojectPoint的文档指出
将z坐标为0.0的点反投影返回近裁剪平面上的点；将z坐标为1.0的点反投影返回远裁剪平面上的点。
虽然它没有明确说明中间点在近平面和远平面之间存在线性关系，但我已经做出了这样的假设，并计算出screenZ的值为z = 0平面位于近裁剪平面和远裁剪平面之间的百分比距离。为了检查我的答案，我可以在三角形的角附近单击，因为我知道它们在全局坐标中的位置。
我的问题是，我没有获得正确的值，并且当我开始更改相机上的zNear和zFar裁剪平面时，我没有获得一致的值。那么我的问题是，我该如何做？最终，我将创建一个新的几何体，并将其放置在对应于用户单击的z平面上。
提前感谢您的帮助。
SCNSceneRenderer.hitTest()？unprojectPoint()的文档甚至提到你应该使用hitTest()处理点击事件。 - bio