swift – 获取节点scenekit中顶点的位置

概述我有一个以编程方式创建的平面,我想获得该平面所具有的一个顶点的坐标.像这样的东西：print(Plane.vertices [1] .position)它可能会打印类似：(x：1,y：1)和print(Plane.vertices [2] .position)打印(x – 1, y：1) 这就是我创造飞机的方式： let positions = [SCNVector3Make( 0, -0.1, 我有一个以编程方式创建的平面,我想获得该平面所具有的一个顶点的坐标.像这样的东西：print(Plane.vertices [1] .position)它可能会打印类似：(x：1,y：1)和print(Plane.vertices [2] .position)打印(x – 1,y：1)

这就是我创造飞机的方式：

let positions = [SCNVector3Make(  0,-0.1,0),SCNVector3Make(  0.3,SCNVector3Make(  0,0.1,]        let indices :[UInt16] = [            0,1,2,3,]        let vertexSource = SCNGeometrySource(vertices: positions,count: 4)        let indexData = NSData(bytes: indices,length: MemoryLayout<CInt>.size * indices.count)        let newElement = SCNGeometryElement(data: NSData(bytes: indices,length: indices.count * MemoryLayout<Int16>.size) as Data,primitiveType: .triangles,primitiveCount: 2,bytesPerIndex: MemoryLayout<Int16>.size)        let geometry = SCNGeometry(sources: [vertexSource],elements: [newElement])        custom = SCNNode(geometry: geometry)        scene.rootNode.addChildNode(custom!)        custom?.position = SCNVector3Make(0,0)

我认为这可以通过变换完成,但是自定义变换有很多奇怪的东西,比如m11,m12,m13,我不明白.

解决方法 这是一个比初看起来更复杂的问题.

SceneKit将存储用于以原始比例/基础生成节点的几何体的坐标.创建对象后,这些不会更改.对于像SCNPlane或SCNBox这样的原语,这些几何在场景中共享.因此,如果您有一堆不同的平面或框,所有处于不同的位置,旋转和缩放,当您查询SCNGeometrySource时,您将获得相同的顶点.这里有一个很好的讨论检索：Extracting vertices from scenekit.但是这种方法不会给你本地坐标空间的角落.

我们有两个适用于SCNNode和SCNGeometry的函数：boundingBox和boundingSphere(它们在协议SCNBoundingVolume中定义). boundingBox为您提供两个点,最小值和最大值.从立方体的两个相对角,您可以找出平面的角顶点.但是还有另一个复杂因素.这两个函数都在本地坐标(节点本身使用的坐标系)中返回它们的答案.所以我们仍然卡住了：我的每架飞机或箱子都有相同的边界框.

我想出的答案是使用SCNNode的convertposition(_,to：node),传递场景的根节点.这最终给了我根节点坐标空间中的边界框.

for node in [custom1,custom2,plainPlane1,plainPlane2] {    print(node.name!)    print(node.boundingBox.max)    print(node.boundingBox.min)    print(node.convertposition(node.boundingBox.min,to: scene.rootNode))    print(node.convertposition(node.boundingBox.max,to: scene.rootNode))}

生产

custom 1SCNVector3(x: 0.300000011920929,y: 0.100000001490116,z: 0.0)SCNVector3(x: 0.0,y: -0.100000001490116,z: -1.0)SCNVector3(x: 0.300000011920929,z: -1.0)custom 2SCNVector3(x: 0.300000011920929,z: 0.0)SCNVector3(x: 0.200000002980232,y: 0.429289322037836,z: -1.07071067796216)SCNVector3(x: 0.500000014901161,y: 0.570710677962164,z: -0.929289322037836)plain plane 1SCNVector3(x: 0.5,y: 1.0,z: 0.0)SCNVector3(x: -0.5,y: -1.0,z: -2.0)SCNVector3(x: 0.5,z: -2.0)plain plane 2SCNVector3(x: 0.5,z: 0.0)SCNVector3(x: -9.18485139438876e-18,y: -0.300000011920929,z: -1.84999999403954)SCNVector3(x: 9.18485139438876e-18,y: 0.300000011920929,z: -2.15000000596046)

对于这个场景：

这是下面的完整macOS游乐场：

//: Playground - noun: a place where people can playimport Cocoaimport SceneKitimport PlaygroundSupportlet positions = [SCNVector3Make(  0,]let indices :[UInt16] = [    0,]let vertexSource = SCNGeometrySource(vertices: positions,count: 4)let indexData = NSData(bytes: indices,length: MemoryLayout.size * indices.count)let newElement = SCNGeometryElement(data: NSData(bytes: indices,length: indices.count * MemoryLayout.size) as Data,bytesPerIndex: MemoryLayout.size)let sceneVIEw = SCNVIEw(frame: CGRect(x: 0,y: 0,wIDth: 600,height: 400))sceneVIEw.allowsCameraControl = truesceneVIEw.autoenablesDefaultlighting = truesceneVIEw.backgroundcolor = NScolor.darkGraysceneVIEw.showsstatistics = truePlaygroundPage.current.liveVIEw = sceneVIEwlet scene = SCNScene()sceneVIEw.scene = scenelet geometry = SCNGeometry(sources: [vertexSource],elements: [newElement])geometry.firstMaterial?.diffuse.contents = NScolor.redgeometry.firstMaterial?.isDoubleSIDed = truelet custom1 = SCNNode(geometry: geometry)custom1.position = SCNVector3Make(0,-1)custom1.name = "custom 1"scene.rootNode.addChildNode(custom1)let custom2 = SCNNode(geometry: geometry)custom2.position = SCNVector3Make(0.2,0.5,-1)custom2.rotation = SCNVector4Make(1,CGfloat(M_PI_4))custom2.name = "custom 2"scene.rootNode.addChildNode(custom2)let plainPlaneGeometry = SCNPlane(wIDth: 1,height: 2)plainPlaneGeometry.firstMaterial?.diffuse.contents = NScolor.yellowplainPlaneGeometry.firstMaterial?.isDoubleSIDed = truelet plainPlane1 = SCNNode(geometry: plainPlaneGeometry)plainPlane1.position = SCNVector3Make(0,-2)plainPlane1.name = "plain plane 1"scene.rootNode.addChildNode(plainPlane1)let plainPlane2 = SCNNode(geometry: plainPlaneGeometry)plainPlane2.position = SCNVector3Make(0,-2)plainPlane2.rotation = SCNVector4Make(0,CGfloat(M_PI_2))plainPlane2.scale = SCNVector3Make(0.3,0.3,0.3)plainPlane2.name = "plain plane 2"scene.rootNode.addChildNode(plainPlane2)for node in [custom1,plainPlane2] {    print(node.name!)    print(node.boundingBox.max)    print(node.boundingBox.min)//  print(node.transform)    print(node.convertposition(node.boundingBox.min,to: scene.rootNode))}

你提到了转换矩阵.有一个很好的解释它看起来是什么样的,它是如何在Need better and simpler understanding of CATransform3D工作的(引用了两篇优秀的维基百科文章),以及一个易于理解的概述于http://sketchytech.blogspot.com/2014/12/explaining-catransform3d-matrix.html.

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