SceneKit particleSystem.handle Swift3 implementation of Objective-C code @ https://developer.apple.com/documentation/scenekit/scnparticleeventblock

gistfile1.txt

/*
 dataStride property notes
 16  color              color[0] color[1] color[2] color[3] RGBA array of four float values
 16  angle              angle[0] -- single float value
 12  rotationAxis       rotationAxis[0], rotationAxis[1], rotationAxis[2] array of three float values
 16  angularVelocity    angularVeclocity[0] -- single float value
 16  velocity           velocity[0], velocity[1], velocity[2] -- array of three float values
 12  contactNormal      contactNormal[0], contactNormal[1], contactNormal[2] -- array of three float values
*/
particleSystem.handle(SCNParticleEvent.collision, forProperties:
            [SCNParticleSystem.ParticleProperty.angle,          // data[0]
                SCNParticleSystem.ParticleProperty.rotationAxis,   // data[1]
                SCNParticleSystem.ParticleProperty.angularVelocity,// data[2]
                SCNParticleSystem.ParticleProperty.velocity,       // data[3]
                SCNParticleSystem.ParticleProperty.contactNormal]  // data[4]
        ) { (data:UnsafeMutablePointer<UnsafeMutableRawPointer>, dataStride:UnsafeMutablePointer<Int>, indicies:UnsafeMutablePointer<UInt32>?, count:Int) in
            
            for i in 0..<count {
                
                // fix orientation
                let anglePointer = data[0] + dataStride[0] * Int(indicies![i])
                let floatPtr0 = anglePointer.bindMemory(to: Float.self, capacity: dataStride[0])
                let angleBuffer = UnsafeMutableBufferPointer(start: floatPtr0, count: dataStride[0])
                
                let rotationAxisPointer = data[1] + dataStride[1] * Int(indicies![i])
                let floatPointer1 = rotationAxisPointer.bindMemory(to: Float.self, capacity: dataStride[1])
                let rotationAxisBuffer = UnsafeMutableBufferPointer(start: floatPointer1, count: dataStride[1]);
                
                let contactNormalPointer = data[4] + dataStride[4] * Int(indicies![i])
                let floatPointer4 = contactNormalPointer.bindMemory(to: Float.self, capacity: dataStride[4])
                let contactNormalBuffer = UnsafeMutableBufferPointer(start: floatPointer4, count: dataStride[4]);
                
                let collisionNormal = SCNVector3Make(contactNormalBuffer[0], contactNormalBuffer[1], contactNormalBuffer[2])
                let crossProduct = SCNVector3CrossProduct(left: collisionNormal, right: SCNVector3Make(0,0,1));
                let crossProductLength = SCNVector3Length(vector: crossProduct)
                angleBuffer[0] = asin(crossProductLength)
                
                rotationAxisBuffer[0] = crossProduct.x / crossProductLength;
                rotationAxisBuffer[1] = crossProduct.y / crossProductLength;
                rotationAxisBuffer[2] = crossProduct.z / crossProductLength;
                
                // kill the angular rotation
                let angularVelocityPointer = data[2] + dataStride[2] * Int(indicies![i])
                let floatPointer2 = angularVelocityPointer.bindMemory(to: Float.self, capacity: dataStride[2])
                let angularVelocityBuffer = UnsafeMutableBufferPointer(start: floatPointer2, count: dataStride[2]);
                angularVelocityBuffer[0] = 0;
                
                if(contactNormalBuffer[1] > 0.4) {
                    let velocityPointer = data[3] + dataStride[3] * Int(indicies![i])
                    let floatPointer3 = velocityPointer.bindMemory(to: Float.self, capacity: dataStride[3])
                    let velocityBuffer = UnsafeMutableBufferPointer(start: floatPointer3, count: dataStride[3]);
                    velocityBuffer[0] = 0
                    velocityBuffer[1] = 0
                    velocityBuffer[2] = 0
                }
            }
        }