Air Hockey circle-circle impulse on collision in Swift/SpriteKit? - swift

Question

Background: I'm working on a simple game/application in SpriteKit (Swift). It's similar to Air Hockey but with magnets (like tabletop game called Klask). I have already spent a lot of time adding a store, ads, menu, etc. It's been a fun learning project for me so far.
Current method: I am applying an impulse to a ball when the player/mallet strikes the ball. This impulse (which takes in a CGVector(dx:.., dy:..)) is calculated by the touch movement/position frame to frame. So for instance, if the player moved the mallet in the north east direction and a collision between the ball and the player is detected, the ball will move in that northeast direct (up and to the right).
Issue: This doesn't take into account when the player clips the ball, which causes a warpy effect.The player would expect the ball to move in a direction based on where the ball strikes on the players mallet (a round circle) rather than the direction of the touch (which does usually work pretty well).
Desired implementation (demo from acceleroto's Air Hockey):
Current implementation/code:
// In player class
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?)
{
bottomTouchIsActive = true
var releventTouch:UITouch!
//convert set to known type
let touchSet = touches
//get array of touches so we can loop through them
let orderedTouches = Array(touchSet)
for touch in orderedTouches
{
//if we've not yet found a relevent touch
if releventTouch == nil
{
//look for a touch that is in the activeArea (Avoid touches by opponent)
if activeArea.contains(CGPoint(x: touch.location(in: parent!).x, y: touch.location(in: parent!).y + frame.height * 0.24))
{
isUserInteractionEnabled = true
releventTouch = touch
}
else
{
releventTouch = nil
}
}
}
if (releventTouch != nil) && lastTouchTimeStamp != nil
{
//get touch position and relocate player
let location = CGPoint(x: releventTouch!.location(in: parent!).x, y: releventTouch!.location(in: parent!).y + frame.height * 0.24)
position = location
//find old location and use pythagoras to determine length between both points
let oldLocation = CGPoint(x: releventTouch!.previousLocation(in: parent!).x, y: releventTouch!.previousLocation(in: parent!).y + frame.height * 0.24)
let xOffset = location.x - oldLocation.x
let yOffset = location.y - oldLocation.y
let vectorLength = sqrt(xOffset * xOffset + yOffset * yOffset)
let seconds = releventTouch.timestamp - lastTouchTimeStamp!
let velocity = 0.015 * Double(vectorLength) / seconds
//to calculate the vector, the velcity needs to be converted to a CGFloat
let velocityCGFloat = CGFloat(velocity)
// NSUserDefaults for more direct access in collision detection
let forceSaveDX = UserDefaults.standard
forceSaveDX.set(velocityCGFloat * xOffset / vectorLength, forKey: "BottomForceDX")
forceSaveDX.synchronize()
let forceSaveDY = UserDefaults.standard
forceSaveDY.set(velocityCGFloat * yOffset / vectorLength, forKey: "BottomForceDY")
forceSaveDY.synchronize()
//Only apply an impulse if the touch is active.
delegate?.bottomTouchIsActive(bottomTouchIsActive, fromBottomPlayer: self)
//update latest touch time for next calculation
lastTouchTimeStamp = releventTouch.timestamp
}
else if (releventTouch != nil) && lastTouchTimeStamp == nil
{
//get touch position and relocate player
let location = CGPoint(x: releventTouch!.location(in: parent!).x, y: releventTouch!.location(in: parent!).y + frame.height * 0.24)
position = location
//find old location and use pythagoras to determine length between both points
let oldLocation = CGPoint(x: releventTouch!.previousLocation(in: parent!).x, y: releventTouch!.previousLocation(in: parent!).y + frame.height * 0.24)
let xOffset = location.x - oldLocation.x
let yOffset = location.y - oldLocation.y
let vectorLength = sqrt(xOffset * xOffset + yOffset * yOffset)
//update latest touch time for next calculation
lastTouchTimeStamp = releventTouch.timestamp
}
}
// In main gameScene
func didBegin(_ contact: SKPhysicsContact)
{
if (contact.bodyA.categoryBitMask == BodyType.ball.rawValue && contact.bodyB.categoryBitMask == BodyType.player.rawValue) && (contact.bodyA.contactTestBitMask == 25 || contact.bodyB.contactTestBitMask == 25) && bottomTouchForCollision == true
{
ball!.physicsBody!.applyImpulse(CGVector(dx: CGFloat(UserDefaults.standard.float(forKey: "BottomForceDX")), dy: CGFloat(UserDefaults.standard.float(forKey: "BottomForceDY"))))
}
}
I apologize for the long question, it's hard to explain what the issue is. But essentially I just need to make the impulse be calculated using where the ball hits the player mallet rather than by the direction of the touch. If this can be done directly in the collision detection function, that would be even better as there would be no extra frame dedicated to calculating the touch direction. I've been stuck for a while.
I think it would be best to incorporate the speed of the touch and the position where the ball strikes the mallet to have the most realistic impulse. I just don't know how to calculate the vector this way. I'm open to all ideas!