SpriteKit physics in Swift - Ball slides against wall instead of reflecting

Question

I have been creating my own very simple test game based on Breakout while learning SpriteKit (using iOS Games by Tutorials by Ray Wenderlich et al.) to see if I can apply co

Answer 1

I came up with a temporary solution that is working surprisingly well. Simply apply a very small impulse opposite of the border. You may need to change the strength based on the masses in your system.

func didBeginContact(contact: SKPhysicsContact) {

    let otherNode = contact.bodyA.node == ball.sprite ? contact.bodyB.node : contact.bodyA.node

    if let obstacle = otherNode as? Obstacle {
        ball.onCollision(obstacle)
    }
    else if let border = otherNode as? SKSpriteNode {

        assert(border.name == "border", "Bad assumption")

        let strength = 1.0 * (ball.sprite.position.x < frame.width / 2 ? 1 : -1)
        let body = ball.sprite.physicsBody!
        body.applyImpulse(CGVector(dx: strength, dy: 0))
    }
}

In reality, this should not be necessary, since as described in the question, frictionless, fully elastic collision dictates that the ball should rebound by inverting the x velocity (assuming side borders) no matter how small the collision angle is.

Instead, what is happening in the game is as if sprite kit ignores the X velocity if it is smaller than a certain value, making the ball slide against the wall without rebound.

Final Note

After reading this and this, it's obvious to me that the real answer is for any serious physics game you have, you should be using Box2D instead. You get way too many perks from the migration.