Slow CPU-based Drawing

SlowCPU-based.swift

class FreedrawingImageViewCG: UIImageView {
    
    var currentTouchPosition: CGPoint?
    
    override func layoutSubviews() {
        super.layoutSubviews()
        isUserInteractionEnabled = true
    }
    
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        super.touchesBegan(touches, with: event)
        guard let newTouchPoint = touches.first?.location(in: self) else { return }
        currentTouchPosition = newTouchPoint
    }
    
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let newTouchPoint = touches.first?.location(in: self) else { return }
        guard let previousTouchPoint = currentTouchPosition else { return }
        
        let renderer = UIGraphicsImageRenderer(size: bounds.size)
        
        image = renderer.image { ctx in
            image?.draw(in: bounds)
            UIColor.red.setStroke()
            ctx.cgContext.setLineCap(.round)
            ctx.cgContext.setLineWidth(5)
            ctx.cgContext.move(to: previousTouchPoint)
            ctx.cgContext.addLine(to: newTouchPoint)
            ctx.cgContext.strokePath()
        }
        
        currentTouchPosition = newTouchPoint
    }
    
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        currentTouchPosition = nil
    }
}