swift - 如何在 SceneKit 中的两点之间画一条线？

Question

如果我在 SceneKit 中有两个点(例如 (1,2,3) 和 (-1,-1,-1))。如何在两者之间划清界线？

我看到有一个我可以使用的 SCNBox 对象，但它只允许我指定中心(例如通过 simdPosition)。修改它的其他方法是变换(我不知道如何使用)或欧拉角(我不确定如何计算我需要使用哪些)。

Answer 1

You can draw a line between two points using the following approach:

import SceneKit

extension SCNGeometry {

    class func line(vector1: SCNVector3,
                    vector2: SCNVector3) -> SCNGeometry {

        let sources = SCNGeometrySource(vertices: [vector1,
                                                   vector2])
        let index: [Int32] = [0,1]

        let elements = SCNGeometryElement(indices: index,
                                    primitiveType: .line)

        return SCNGeometry(sources: [sources],
                          elements: [elements])
    }
}

...然后将其提供给 ViewController 中的 addLine 函数:

class ViewController: UIViewController { 

    // Some code...

    func addLine(start: SCNVector3, end: SCNVector3) {
        let lineGeo = SCNGeometry.line(vector1: start,
                                       vector2: end)
        let lineNode = SCNNode(geometry: lineGeo)
        sceneView.scene.rootNode.addChildNode(lineNode)
    }
}

As we all know line's width can't be changed (cause there's no property to do it), so you can use cylinder primitive geometry instead of a line:

extension SCNGeometry {

    class func cylinderLine(from: SCNVector3, 
                              to: SCNVector3,
                        segments: Int) -> SCNNode {

        let x1 = from.x
        let x2 = to.x

        let y1 = from.y
        let y2 = to.y

        let z1 = from.z
        let z2 = to.z

        let distance =  sqrtf( (x2-x1) * (x2-x1) +
                               (y2-y1) * (y2-y1) +
                               (z2-z1) * (z2-z1) )

        let cylinder = SCNCylinder(radius: 0.005,
                                   height: CGFloat(distance))

        cylinder.radialSegmentCount = segments

        cylinder.firstMaterial?.diffuse.contents = UIColor.green

        let lineNode = SCNNode(geometry: cylinder)

        lineNode.position = SCNVector3(x: (from.x + to.x) / 2,
                                       y: (from.y + to.y) / 2,
                                       z: (from.z + to.z) / 2)

        lineNode.eulerAngles = SCNVector3(Float.pi / 2,
                                          acos((to.z-from.z)/distance),
                                          atan2((to.y-from.y),(to.x-from.x)))

        return lineNode
    }
}

...然后以相同的方式将其提供给 ViewController:

class ViewController: UIViewController { 

    // Some code...

    func addLine(start: SCNVector3, end: SCNVector3) {

        let cylinderLineNode = SCNGeometry.cylinderLine(from: start, 
                                                          to: end, 
                                                    segments: 3)

        sceneView.scene.rootNode.addChildNode(cylinderLineNode)
    }
}