Contact physics Gap in SpriteKit (Swift) - ios

Question

I am working on my first swift iOS sprite kit project but I've run into a problem that I just can't find a solution to. My goal is to have a ball land on a moving platform and the ball and platform both stop upon contact.
The issue I am running into is that there is consistently a gap between the platform and ball when the code recognizes they are in contact and makes them stop. See the attached photo:
Image Here
Ball:
//Ball Node
func createPlayer() -> SKNode {
let playerNode = SKNode()
playerNode.position = CGPoint(x: self.size.width / 2, y: self.size.height * 0.25)
let sprite = SKSpriteNode(imageNamed: "ball")
sprite.setScale(scaleFactor)
playerNode.addChild(sprite)
playerNode.physicsBody = SKPhysicsBody(circleOfRadius: sprite.size.width / 2)
playerNode.physicsBody?.dynamic = false
playerNode.physicsBody?.allowsRotation = false
playerNode.physicsBody?.restitution = 0.0
playerNode.physicsBody?.friction = 0.0
playerNode.physicsBody?.angularDamping = 0.0
playerNode.physicsBody?.linearDamping = 0.0
playerNode.physicsBody?.usesPreciseCollisionDetection = true
playerNode.physicsBody?.categoryBitMask = CollisionCategoryBitmask.Player
playerNode.physicsBody?.collisionBitMask = 0
playerNode.physicsBody?.contactTestBitMask = CollisionCategoryBitmask.Platform | CollisionCategoryBitmask.Vortex
return playerNode
Platform:
//Platform
sprite = SKSpriteNode(imageNamed: "platform")
let node = PlatformNode()
let thePosition = CGPoint(x: position.x * scaleFactor - (sprite.size.width / 1.999), y: position.y + (self.size.height * 0.50))
sprite.setScale(scaleFactor)
node.addChild(sprite)
node.physicsBody?.usesPreciseCollisionDetection = true
node.physicsBody = SKPhysicsBody(rectangleOfSize: sprite.size)
node.physicsBody?.dynamic = false
node.physicsBody?.categoryBitMask = CollisionCategoryBitmask.Platform
node.physicsBody?.collisionBitMask = 0
return node
didBeginContact:
func didBeginContact(contact: SKPhysicsContact) {
var updateHUD = true
maxPlayerY = Int(player.position.y)
let whichNode = (contact.bodyA.node != player) ? contact.bodyA.node : contact.bodyB.node
//If the ball is falling
if player.physicsBody?.velocity.dy < 0 {
let other = whichNode as! GameObjectNode
//If the player hits the Platform
if player.physicsBody?.velocity.dy < 0 && whichNode?.name == "NODE_PLATFORM" {
let joint = SKPhysicsJointFixed.jointWithBodyA(player.physicsBody, bodyB:whichNode!.physicsBody, anchor:CGPoint(x: player.position.x, y: ballBottom))
let moveScreen = SKAction.moveToY(-(player.position.y - 200), duration: 0.5)
let moveVortex = SKAction.moveToY((player.position.y - scaleFactor*300), duration: 0.5)
physicsWorld.addJoint(joint
player.physicsBody?.velocity = CGVector(dx: player.physicsBody!.velocity.dx, dy: 0)
player.physicsBody?.affectedByGravity = false
}
}
}

Answer 1

I suspect you can resolve this issue by waiting until after the physics simulation has completed (for the current frame) before connecting the objects. One way to do that is to a set a flag when the ball is in contact with the platform in didBeginContact and then connect the two bodies with a joint in didSimulatePhysics.