How to recognize a screen high-five - ios

Question

I have a client that wants to recognize when an user smacks their screen with their whole hand, like a high-five. I suspect that Apple won't approve this, but let's look away from that.
I though of using a four-finger-tap recognizer, but that doesn't really cover it. The best approach would possibly be to check if the user is covering at least 70% of the screen with their hand, but I don't know how to do that.
Can someone help me out here?

Answer 1

You could use the accelerometer to detect the impact of a hand & examine the front camera feed to find a corresponding dark frame due to the hand covering the camera*
* N.B. a human hand might not be big enough to cover the front camera on an iPhone 6+

Answer 2

Sort of solved it. Proximity + accelerometer works good enough. Multitouch doesn't work, as it ignores stuff it doesn't think of as taps.
import UIKit
import CoreMotion
import AVFoundation
class ViewController: UIViewController {
var lastHighAccelerationEvent:NSDate? {
didSet {
checkForHighFive()
}
}
var lastProximityEvent:NSDate? {
didSet {
checkForHighFive()
}
}
var lastHighFive:NSDate?
var manager = CMMotionManager()
override func viewDidLoad() {
super.viewDidLoad()
//Start disabling the screen
UIDevice.currentDevice().proximityMonitoringEnabled = true
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(proximityChanged), name: UIDeviceProximityStateDidChangeNotification, object: nil)
//Check for acceloremeter
manager.startAccelerometerUpdatesToQueue(NSOperationQueue.mainQueue()) { (data, error) in
let sum = abs(data!.acceleration.y + data!.acceleration.z + data!.acceleration.x)
if sum > 3 {
self.lastHighAccelerationEvent = NSDate()
}
}
//Enable multitouch
self.view.multipleTouchEnabled = true
}
func checkForHighFive() {
if let lastHighFive = lastHighFive where abs(lastHighFive.timeIntervalSinceDate(NSDate())) < 1 {
print("Time filter")
return
}
guard let lastProximityEvent = lastProximityEvent else {return}
guard let lastHighAccelerationEvent = lastHighAccelerationEvent else {return}
if abs(lastProximityEvent.timeIntervalSinceDate(lastHighAccelerationEvent)) < 0.1 {
lastHighFive = NSDate()
playBoratHighFive()
}
}
func playBoratHighFive() {
print("High Five")
let player = try! AudioPlayer(fileName: "borat.mp3")
player.play()
}
func proximityChanged() {
if UIDevice.currentDevice().proximityState {
self.lastProximityEvent = NSDate()
}
}
}

Answer 3

You can detect finger count with multi touch event handling. check this answer