Question

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：print(Plane.vertices[1].position)它可能会打印如下：（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, -0.1,  0),

                         SCNVector3Make(  0,  0.1,  0),
                         SCNVector3Make(  0.3,  0.1,  0),
                         ]
        let indices :[UInt16] = [

            0, 1, 2,
            1, 3, 2,
            ]

        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, 0)

我认为这可以通过变换以某种方式完成，但是自定义变换有很多奇怪的东西，比如m11，m12，m13，我不明白。

Answer 1

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。一旦创建了对象，那些就不会改变。对于SCNPlane或SCNBox等基元，这些几何在场景中共享。因此，如果您有一堆不同的平面或方框，所有位于不同的位置，旋转和缩放，当您查询SCNGeometrySource时，您将获得相同的顶点。这里有一个关于该检索的很好的讨论：Extracting vertices from scenekit。但是这种方法不会给你当地坐标空间的角落。

我们有两个适用于SCNNode和SCNGeometry的功能：boundingBox和boundingSphere（它们在协议SCNBoundingVolume中定义）。 boundingBox为您提供两点，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。所以我们仍然陷入困境：我的每一架飞机或箱子都有相同的边界框。

我想出的答案是使用SCNNode＆＃39; convertPosition(_, to: node)，传递场景的根节点。这最终给了我在根节点的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))
}

制造

custom 1
SCNVector3(x: 0.300000011920929, y: 0.100000001490116, z: 0.0)
SCNVector3(x: 0.0, y: -0.100000001490116, z: 0.0)
SCNVector3(x: 0.0, y: -0.100000001490116, z: -1.0)
SCNVector3(x: 0.300000011920929, y: 0.100000001490116, z: -1.0)
custom 2
SCNVector3(x: 0.300000011920929, y: 0.100000001490116, z: 0.0)
SCNVector3(x: 0.0, y: -0.100000001490116, 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 1
SCNVector3(x: 0.5, y: 1.0, z: 0.0)
SCNVector3(x: -0.5, y: -1.0, z: 0.0)
SCNVector3(x: -0.5, y: -1.0, z: -2.0)
SCNVector3(x: 0.5, y: 1.0, z: -2.0)
plain plane 2
SCNVector3(x: 0.5, y: 1.0, z: 0.0)
SCNVector3(x: -0.5, y: -1.0, 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)

这个场景：

以下是完整的macOS游乐场：

//: Playground - noun: a place where people can play

import Cocoa
import SceneKit
import PlaygroundSupport

let positions = [SCNVector3Make(  0, -0.1,  0),
                 SCNVector3Make(  0.3, -0.1,  0),
                 SCNVector3Make(  0,  0.1,  0),
                 SCNVector3Make(  0.3,  0.1,  0),
]
let indices :[UInt16] = [
    0, 1, 2,
    1, 3, 2,
]

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,
                                    primitiveType: .triangles ,
                                    primitiveCount: 2, 
                                    bytesPerIndex: MemoryLayout.size)

let sceneView = SCNView(frame: CGRect(x: 0, y: 0, width: 600, height: 400))
sceneView.allowsCameraControl = true
sceneView.autoenablesDefaultLighting = true
sceneView.backgroundColor = NSColor.darkGray
sceneView.showsStatistics = true
PlaygroundPage.current.liveView = sceneView

let scene = SCNScene()
sceneView.scene = scene

let geometry = SCNGeometry(sources: [vertexSource], elements: [newElement])
geometry.firstMaterial?.diffuse.contents = NSColor.red
geometry.firstMaterial?.isDoubleSided = true
let custom1 = SCNNode(geometry: geometry)
custom1.position = SCNVector3Make(0, 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, 0, 0, CGFloat(M_PI_4))
custom2.name = "custom 2"
scene.rootNode.addChildNode(custom2)

let plainPlaneGeometry = SCNPlane(width: 1, height: 2)
plainPlaneGeometry.firstMaterial?.diffuse.contents = NSColor.yellow
plainPlaneGeometry.firstMaterial?.isDoubleSided = true
let plainPlane1 = SCNNode(geometry: plainPlaneGeometry)
plainPlane1.position = SCNVector3Make(0, 0, -2)
plainPlane1.name = "plain plane 1"
scene.rootNode.addChildNode(plainPlane1)

let plainPlane2 = SCNNode(geometry: plainPlaneGeometry)
plainPlane2.position = SCNVector3Make(0, 0, -2)
plainPlane2.rotation = SCNVector4Make(0, 1, 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, custom2, plainPlane1, plainPlane2] {
    print(node.name!)
    print(node.boundingBox.max)
    print(node.boundingBox.min)
//  print(node.transform)
    print(node.convertPosition(node.boundingBox.min, to: scene.rootNode))
    print(node.convertPosition(node.boundingBox.max, to: scene.rootNode))
}

您提到了转换矩阵。在Need better and simpler understanding of CATransform3D处可以很好地解释它的外观及其工作方式（引用两篇优秀的维基百科文章），以及http://sketchytech.blogspot.com/2014/12/explaining-catransform3d-matrix.html上易于理解的概述。

获取节点scenekit中顶点的位置

1 个答案: