SracthCard Touch Handling

ScratchCard-TouchHandling.swift

private var previousLocation: CGPoint?
// 0. Line/LineCollection class is a convenience class to store line(s)
private var lineCollection: LineCollection = LineCollection()

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    // 1. If there is no touch point or if the point did not move, ignore
    guard let touch = touches.first else {
        return
    }
    let location = touch.location(in: self)  
    if location == previousLocation {
        return
    }

    if previousLocation == nil{
        // 2. If this is the first touch point, then create first line with the point
        let line = Line().lineByAdding(point: location)
        lineCollection = lineCollection.lineCollectionByAddingLine(line: line)    
    } else {
        // 3. If this is the second touch point and on, just add the point to the line collection
        lineCollection = lineCollection.lineCollectionByAddingPoint(point: location)
    }
    previousLocation = location
}

override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
    // 4. reset previousLocation
    previousLocation = nil
}