Doodle Draw App: lines drawn keep overlapping when (alpha < 1) - ios

Question

My Swift doodle app works, but when I change the alpha below '1.0', then I draw a line on the screen, the lines keeps overlapping. I created a custom Line class, drawView subclass of UIView. I've been messing around all day but can't seem to figure it out. See Below.
DrawView: UIView class
override func touchesBegan(touches: Set<NSObject>, withEvent event: UIEvent) {
var touch = touches.first as! UITouch
lastPoint = touch.locationInView(self)
}
override func touchesMoved(touches: Set<NSObject>, withEvent event: UIEvent) {
var touch = touches.first as! UITouch
var newPoint = touch.locationInView(self)
//from custom Line class: sets width and opacity as well
lines.append(Line(start: lastPoint, end: newPoint, color: drawColor, brushWidth: brushWidth, opacity: opacity))
lastPoint = newPoint
self.setNeedsDisplay()
}
override func touchesEnded(touches: Set<NSObject>, withEvent event: UIEvent){
touchesMoved(touches, withEvent: event) // adds point
}
override func drawRect(rect: CGRect) {
var context = UIGraphicsGetCurrentContext()
CGContextBeginPath(context)
CGContextSetLineCap(context, kCGLineCapRound)
for line in lines {
CGContextSetLineWidth(context, line.brushWidth)
CGContextSetAlpha(context, line.opacity)
CGContextSetStrokeColorWithColor(context, line.color.CGColor)
CGContextMoveToPoint(context, line.start.x, line.start.y)
CGContextAddLineToPoint(context, line.end.x, line.end.y)
CGContextStrokePath(context)
}
}
I don't know why it keeps overlapping. I some how need to track a the path then draw over it or somehow see if my CGPoints are the same while next to each other remove it or ignore it.
Is this possible using just one UIView?
Just now I tried using:
var touchesEnd: Bool = false //global variable
Then in touchesEnded:
touchesEnd = true
Finally in TouchesMoved:
if touchesEnd == true {
self.setNeedsDisplay()
}
This is the most recent things i've tried but hasn't worked.