Drawing a line between two points using SceneKit

Question

I have two points (let\'s call them pointA and pointB) of type SCNVector3. I want to draw a line between them. Seems like it should be easy, but can\'t find a way to do it.<

Answer 1

Here's a solution using triangles that works independent of the direction of the line. It's constructed using the cross product to get points perpendicular to the line. So you'll need a small SCNVector3 extension, but it'll probably come in handy in other cases, too.

private func makeRect(startPoint: SCNVector3, endPoint: SCNVector3, width: Float ) -> SCNGeometry {
    let dir = (endPoint - startPoint).normalized()
    let perp = dir.cross(SCNNode.localUp) * width / 2

    let firstPoint = startPoint + perp
    let secondPoint = startPoint - perp
    let thirdPoint = endPoint + perp
    let fourthPoint = endPoint - perp
    let points = [firstPoint, secondPoint, thirdPoint, fourthPoint]

    let indices: [UInt16] = [
        1,0,2,
        1,2,3
    ]
    let geoSource = SCNGeometrySource(vertices: points)
    let geoElement = SCNGeometryElement(indices: indices, primitiveType: .triangles)

    let geo = SCNGeometry(sources: [geoSource], elements: [geoElement])
    geo.firstMaterial?.diffuse.contents = UIColor.blue.cgColor
    return geo
}

SCNVector3 extension:

import Foundation
import SceneKit

extension SCNVector3
{
    /**
     * Returns the length (magnitude) of the vector described by the SCNVector3
     */
    func length() -> Float {
        return sqrtf(x*x + y*y + z*z)
    }

    /**
     * Normalizes the vector described by the SCNVector3 to length 1.0 and returns
     * the result as a new SCNVector3.
     */
    func normalized() -> SCNVector3 {
        return self / length()
    }

    /**
      * Calculates the cross product between two SCNVector3.
      */
    func cross(_ vector: SCNVector3) -> SCNVector3 {
        return SCNVector3(y * vector.z - z * vector.y, z * vector.x - x * vector.z, x * vector.y - y * vector.x)
    }
}