Use case of convexSweepTest(with:from:to:options) - ios

Question

The Apple Documentation gave a seemingly straightforward example of how to use the convexSweepTest in Objective C. Unfortunately the example code in the documentation does not (as of now) exist in Swift.
I can move it over to Swift and compile without error, but I cannot get the 'contacts.count' to ever be anything other than zero no matter how many objects (all with a physicsBody) I add to the scene, including the one I'm doing the convexSweepTest with.
I have a layer of static objects with a physicsBody along the x-z axis, with my object I'm doing the convexSweepTest with a positive y value.
For some reason I'm required to add a custom physicsShape in the SCNPhysicsBody(type:shape) constructor (opposed to leaving it as nil as described in the documentation should work) in order to get the convexSweepTest to recognize the physicsShape so it will compile.
Here's a snippet of the code that compiles without compile error but does not work:
let physicsShape = SCNPhysicsShape(node: selectedBlock, options: nil)
selectedBlock.physicsBody = SCNPhysicsBody(type: .dynamic, shape: physicsShape) // why can't I use nil? who knows
// note: 'selectedBlock' has a positive y value ... and there are objects that can be collided with at every y=0 point
let current = selectedBlock.transform
let downBelow = SCNMatrix4Translate(current, 0, -selectedBlock.position.y, 0)
let physicsWorld = SCNPhysicsWorld()
let physicsContacts = physicsWorld.convexSweepTest(with: (selectedBlock.physicsBody?.physicsShape)!, from: current, to: downBelow, options: nil)
print("count \(physicsContacts.count)") // ALWAYS prints zero
I'm looking for a working use case example in Swift with the convexSweepTest method.

Answer 1

You can't create SCNPhysicsWorld yourself, but use the one in the current scene (scene.physicsWorld).

Answer 2

Old post but while I was playing with convexSweepTest I found out that if the collisionBitMask of the other physicbody doesn't have the first bit set it won't return the contact, which makes no sense as the convexSweepTest doesn't have a categorymask or it's defaulted to 1 without saying?
Run the code below in playground
First static node, green, is with a physic body, with its category NOT matching the collisionBitMask of the convexSweep option
Second static node, orange, is with a physic body, with its category matching the collisionBitMask of the convexSweep option
One node is in movement with no physic body, just to visually show where is the shape used in the convexSweep as I'm using the coordinate of the moving node
I move the 'moving' node that represent the convexSweep shape across the 2 static shapes, if it passes through both without contact I set the first bit of the collision mask of the 2nd node and rerun the movement, if it does contact I reset to what the values should be, runs for ever so that you can see the convexSweep in action. You'll see that the convexSweep honor it's collisionBitMask option as only the 2nd node gets a contact (only if the contact node has the first bit).
import SceneKit
import SpriteKit
import PlaygroundSupport
import simd
let sceneView = SCNView(frame: CGRect(x: 0, y: 0, width: 800, height: 600))
PlaygroundPage.current.liveView = sceneView
var scene = SCNScene()
sceneView.scene = scene
sceneView.backgroundColor = SKColor.lightGray
sceneView.debugOptions = .showPhysicsShapes
sceneView.allowsCameraControl = true
sceneView.autoenablesDefaultLighting = true
// a camera
var cameraNode = SCNNode()
cameraNode.camera = SCNCamera()
cameraNode.position = SCNVector3(x: 0, y: 5, z: 5)
scene.rootNode.addChildNode(cameraNode)
// setup a plane just for contrast and look at
let planeNode = SCNNode(geometry: SCNPlane(width: 10, height: 10))
planeNode.geometry?.firstMaterial?.diffuse.contents = UIColor.blue
planeNode.position = SCNVector3(0, -0.5, 0)
planeNode.rotation = SCNVector4Make(1, 0, 0, -.pi/2);
scene.rootNode.addChildNode(planeNode)
// add cmaera constraint to look at the center of the plane
let centerConstraint = SCNLookAtConstraint(target: planeNode)
cameraNode.constraints = [centerConstraint]
let BitMaskContact = 0x0010
let BitMaskMoving = 0x0100 // To show that this needs to be with first bit set to 1
let BitMaskPassThrough = 0x1000
// Add a box to be a contact body
var passthroughNode = SCNNode(geometry: SCNBox(width: 0.5, height: 1.0, length: 1.0, chamferRadius: 5))
passthroughNode.geometry?.firstMaterial?.diffuse.contents = SKColor.green
passthroughNode.name = "passthroughNode static"
passthroughNode.position = SCNVector3(x: 0, y: 0.5, z: 0)
passthroughNode.physicsBody = SCNPhysicsBody(type: .static, shape: nil)
passthroughNode.physicsBody?.categoryBitMask = BitMaskPassThrough
passthroughNode.physicsBody?.collisionBitMask = BitMaskMoving
scene.rootNode.addChildNode(passthroughNode)
// Add a box to be a contact body
var contactNode = SCNNode(geometry: SCNBox(width: 0.5, height: 1.0, length: 1.0, chamferRadius: 5))
contactNode.geometry?.firstMaterial?.diffuse.contents = SKColor.orange
contactNode.name = "contactNode static"
contactNode.position = SCNVector3(x: 1, y: 0.5, z: 0)
contactNode.physicsBody = SCNPhysicsBody(type: .static, shape: nil)
contactNode.physicsBody?.categoryBitMask = BitMaskContact
contactNode.physicsBody?.collisionBitMask = BitMaskMoving
scene.rootNode.addChildNode(contactNode)
// Add a box just to visually see the shape to be used with convexSweepTest
let sweepOriginalPosition = SCNVector3(x: -1, y: 0.5, z: 0)
let sweepGeo = SCNBox(width: 1, height: 0.5, length: 0.5, chamferRadius: 5)
let sweepNode = SCNNode(geometry: sweepGeo)
sweepNode.name = "sweepNode moving"
sweepNode.position = sweepOriginalPosition
let sweepShape = SCNPhysicsShape(geometry: sweepGeo, options: nil)
scene.rootNode.addChildNode(sweepNode)
//let rendererDelegate = RendererDelegate( sweepNode, physicsWorld:scene.physicsWorld)
//sceneView.delegate = rendererDelegate
//scene.physicsWorld.contactDelegate = rendererDelegate
let timer = Timer.scheduledTimer(withTimeInterval: 0.5, repeats: true) { _ in
let start = sweepNode.simdWorldPosition
let velocityX:Float = 0.1
// Where the shape stands now
var from = matrix_identity_float4x4
from.position = start
// Where the shape should move to
var to: matrix_float4x4 = matrix_identity_float4x4
to.position = start + SIMD3<Float>(velocityX, 0, 0)
let options: [SCNPhysicsWorld.TestOption: Any] = [
SCNPhysicsWorld.TestOption.collisionBitMask: BitMaskContact
]
let contacts = scene.physicsWorld.convexSweepTest(
with: sweepShape,
from: SCNMatrix4(from),
to: SCNMatrix4(to),
options: options)
if !contacts.isEmpty {
print( "contact found. reseting contact node collision to normal")
contactNode.physicsBody?.collisionBitMask = BitMaskMoving // 4 <-- set it back to what it should be
passthroughNode.physicsBody?.collisionBitMask = BitMaskPassThrough // 8 <-- set it back to what it should be
sweepNode.position = sweepOriginalPosition
} else {
sweepNode.position.x = sweepNode.position.x + velocityX
if sweepNode.position.x > 2 {
print( "contact missed. reseting contact node collision to | x0001")
contactNode.physicsBody?.collisionBitMask = BitMaskMoving | 0x0001 // 5 <-- have the first bit to 1
passthroughNode.physicsBody?.collisionBitMask = BitMaskPassThrough | 0x0001 // 9 <-- have the first bit to 1, but with convexSweep opion set it won't matter
sweepNode.position = sweepOriginalPosition
}
}
}