Problem with collision detection in Spritekit

You haven't specified that player nodes can also collide with each other (lines 58-60):

        playerNode.physicsBody?.categoryBitMask = CollisionBitMask.playerCategory 
        playerNode.physicsBody?.collisionBitMask = CollisionBitMask.foregroundCategory 
        playerNode.physicsBody?.contactTestBitMask = CollisionBitMask.foregroundCategory

This says that players can only collide with the foreground.

Hello Quincey, I only have one player so this doesn't solve anything. The thing I want is the player to bounce on the foreground. Kr

If you set your GameViewController to showsPhysics to true, when you view the foreground node does it actually have the body you think it does? Always worth checking to make sure that isn't the issue.

As suspected by CartoonSmart, your physics body for the tiles was the wrong shape. This is so often the cause of this kind of issue, therefore, you should always enable showsPhysics on yoru SKView during development. There are additional problems:

1) SKSpriteNode anchorPoint is not used in the manner in which you attempted. It's valid range is [0..1] and refers to its placement with respect to *its* coordinate system, not its parent's.

2) You attempted to create one physics body for all tiles, but creating a physics body for each tile is a better practice for scalability.

the updated code:

import SpriteKit
class GameScene: SKScene {

    struct CollisionBitMask {
        static let playerCategory:UInt32 = 0x1 << 0
        static let foregroundCategory:UInt32 = 0x1 << 1
    }

    var foregroundNode: SKNode!
    var foregroundNode2: SKNode!

    var player: SKNode!
    let scaleFactorPlayer: CGFloat = 10
    let scaleFactorForeground: CGFloat = 4

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override init( size: CGSize ) {
        super.init(size: size)      
    }

    override func didMove(to view: SKView) {
        super.didMove(to: view)     
        physicsWorld.gravity = CGVector(dx: 0.0, dy: -5.0)          
        let positionForeGroundNode = CGPoint(x: 0, y:0);
        foregroundNode = createForegroundNode(position: positionForeGroundNode)
        foregroundNode.zPosition = 2
        addChild(foregroundNode)            
        player = createPlayer()
        player.zPosition = 2
        addChild(player)                    
        player.physicsBody?.applyImpulse(CGVector(dx: 0.0, dy: 0.0))
     
    }

    func createPlayer() -> SKNode {
        let playerNode = SKNode()
        playerNode.position = CGPoint(x: self.size.width * 0.5, y: self.size.height * 0.5)     
        let sprite = SKSpriteNode( texture: nil, color: .blue, size: CGSize( width: 50, height: 50 ) )
        sprite.setScale( scaleFactorPlayer / 10.0)
        playerNode.addChild(sprite)             
        playerNode.physicsBody = SKPhysicsBody(circleOfRadius: sprite.size.width / 2)
        playerNode.physicsBody!.isDynamic = true
        playerNode.physicsBody!.allowsRotation = false
        playerNode.physicsBody!.categoryBitMask = CollisionBitMask.playerCategory
        playerNode.physicsBody!.collisionBitMask = CollisionBitMask.foregroundCategory     
        return playerNode
    }

    func createForegroundNode( position : CGPoint ) -> SKNode {
        let foregroundNode = SKNode()
        let tilesize: CGFloat = 50
        let origin = CGPoint( x: tilesize / 2.0, y: tilesize / 2.0 )
        let tilesWide = Int( UIScreen.main.bounds.size.width / tilesize )
        for index in 0...tilesWide {          
            var color: SKColor!
            if index % 2 == 0 { color = .brown } else { color = .green }
            let node = SKSpriteNode( texture: nil, color: color, size: CGSize( width: tilesize, height: tilesize ) )                      
            node.position = CGPoint(x: origin.x + position.x + node.size.width * CGFloat(index), y: origin.y + position.y + 0) /          
            node.physicsBody = SKPhysicsBody(rectangleOf: CGSize(width: node.size.width, height: node.size.height))
            node.physicsBody!.isDynamic = false
            node.physicsBody!.categoryBitMask = CollisionBitMask.foregroundCategory
            node.physicsBody!.collisionBitMask = CollisionBitMask.playerCategory
            foregroundNode.addChild( node )
        }
        return foregroundNode
    }
}