DrawView.swift

import UIKit
import CoreGraphics

public class DrawView: UIView {
    
    @IBInspectable public var drawColor: UIColor = .black
    @IBInspectable public var lineWidth: CGFloat = 3
    
    private lazy var lastPoint: CGPoint = .zero
    
    private lazy var bezierPath: UIBezierPath = {
        let path = UIBezierPath()
        path.lineCapStyle = .round
        path.lineJoinStyle = .round
        return path
    }()
    
    // MARK: - Lifecycle Methods
    
    override public func draw(_ rect: CGRect) {
        super.draw(rect)
        
        drawColor.setStroke()
        
        bezierPath.lineWidth = lineWidth
        bezierPath.stroke()
    }
    
    // MARK: - Touch Handling Methods
    
    public override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        super.touchesBegan(touches, with: event)
        guard let point = touches.first?.location(in: self) else { return }
        lastPoint = point
    }
    
    public override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        super.touchesMoved(touches, with: event)
        guard let newPoint = touches.first?.location(in: self) else { return }
        
        bezierPath.move(to: lastPoint)
        bezierPath.addLine(to: newPoint)
        lastPoint = newPoint
        
        setNeedsDisplay()
    }
    
    public override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        super.touchesEnded(touches, with: event)
        setNeedsDisplay()
    }

    public override func touchesCancelled(_ touches: Set<UITouch>, with event: UIEvent?) {
        super.touchesCancelled(touches, with: event)
        setNeedsDisplay()
    }
    
    // MARK: - Public Methods
    
    public func clear() {
        bezierPath.removeAllPoints()
        setNeedsDisplay()
    }
    
    public func hasDraw() -> Bool {
        return !bezierPath.isEmpty
    }
    
    public func renderToImage() -> UIImage? {
        UIGraphicsBeginImageContext(frame.size)
        defer {
            UIGraphicsEndImageContext()
        }
        
        drawColor.setStroke()
        
        bezierPath.lineWidth = lineWidth
        bezierPath.stroke()
        
        return UIGraphicsGetImageFromCurrentImageContext()
    }
    
    public func renderFitToImage() -> UIImage? {
        UIGraphicsBeginImageContext(bezierPath.bounds.size)
        defer {
            UIGraphicsEndImageContext()
        }
        
        let origin = bezierPath.bounds.origin
        bezierPath.apply(CGAffineTransform(
            translationX: -origin.x,
            y: -origin.y
        ))
        
        drawColor.setStroke()
        
        bezierPath.lineWidth = lineWidth
        bezierPath.stroke()
        
        return UIGraphicsGetImageFromCurrentImageContext()
    }
    
}