How do I draw on an image in Swift?

Question

I need to be able to programmatically draw on an image, and save that image for later use. Say, draw a line on specific x and y coordinates on the image, save the image, and

Answer 1

Details

Xcode 9.1, Swift 4

Solution

extension UIImage

extension UIImage {

    typealias RectCalculationClosure = (_ parentSize: CGSize, _ newImageSize: CGSize)->(CGRect)

    func with(image named: String, rectCalculation: RectCalculationClosure) -> UIImage {
        return with(image: UIImage(named: named), rectCalculation: rectCalculation)
    }

    func with(image: UIImage?, rectCalculation: RectCalculationClosure) -> UIImage {

        if let image = image {
            UIGraphicsBeginImageContext(size)

            draw(in: CGRect(origin: .zero, size: size))
            image.draw(in: rectCalculation(size, image.size))

            let newImage = UIGraphicsGetImageFromCurrentImageContext()
            UIGraphicsEndImageContext()
            return newImage!
        }
        return self
    }
}

extension UIImageView

    extension UIImageView {

    enum ImageAddingMode {
        case changeOriginalImage
        case addSubview
    }

    func drawOnCurrentImage(anotherImage: UIImage?, mode: ImageAddingMode, rectCalculation: UIImage.RectCalculationClosure) {

        guard let image = image else {
            return
        }

        switch mode {
        case .changeOriginalImage:
            self.image = image.with(image: anotherImage, rectCalculation: rectCalculation)

        case .addSubview:
            let newImageView = UIImageView(frame: rectCalculation(frame.size, image.size))
            newImageView.image = anotherImage
            addSubview(newImageView)
        }
    }
}

---

Images samples

Parent Image:

Child Image:

---

Usage example 1

func sample1(imageView: UIImageView) {
    imageView.contentMode = .scaleAspectFit
    imageView.image = UIImage(named: "parent")?.with(image: "child") { parentSize, newImageSize in
        print("parentSize = \(parentSize)")
        print("newImageSize = \(newImageSize)")
        return CGRect(x: 50, y: 50, width: 90, height: 90)
    }
}

Result 1

---

Usage example 2

func sample2(imageView: UIImageView) {
    imageView.contentMode = .scaleAspectFit
    imageView.image = UIImage(named: "parent")
    imageView.drawOnCurrentImage(anotherImage: UIImage(named: "child"), mode: .changeOriginalImage) { parentSize, newImageSize in
        print("parentSize = \(parentSize)")
        print("newImageSize = \(newImageSize)")
        let sideLength:CGFloat = 90
        let indent:CGFloat = 50
        return CGRect(x: parentSize.width-sideLength-indent, y: parentSize.height-sideLength-indent, width: sideLength, height: sideLength)
    }
}

Result 2

---

Usage example 3

func sample3(imageView: UIImageView) {
    imageView.contentMode = .scaleAspectFill
    imageView.clipsToBounds = true
    imageView.image = UIImage(named: "parent")
    imageView.drawOnCurrentImage(anotherImage: UIImage(named: "child"), mode: .addSubview) { parentSize, newImageSize in
        print("parentSize = \(parentSize)")
        print("newImageSize = \(newImageSize)")
        let sideLength:CGFloat = 90
        let indent:CGFloat = 15
        return CGRect(x: parentSize.width-sideLength-indent, y: indent, width: sideLength, height: sideLength)
    }
}

Result 3

Full sample code

Don't forget to add Solution code here

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        let imageView = UIImageView(frame: UIScreen.main.bounds)
        view.addSubview(imageView)
        sample1(imageView: imageView)
       // sample2(imageView: imageView)
       // sample3(imageView: imageView)
    }

    func sample1(imageView: UIImageView) {
        imageView.contentMode = .scaleAspectFit
        imageView.image = UIImage(named: "parent")?.with(image: "child") { parentSize, newImageSize in
            print("parentSize = \(parentSize)")
            print("newImageSize = \(newImageSize)")
            return CGRect(x: 50, y: 50, width: 90, height: 90)
        }
    }

    func sample2(imageView: UIImageView) {
        imageView.contentMode = .scaleAspectFit
        imageView.image = UIImage(named: "parent")
        imageView.drawOnCurrentImage(anotherImage: UIImage(named: "child"), mode: .changeOriginalImage) { parentSize, newImageSize in
            print("parentSize = \(parentSize)")
            print("newImageSize = \(newImageSize)")
            let sideLength:CGFloat = 90
            let indent:CGFloat = 50
            return CGRect(x: parentSize.width-sideLength-indent, y: parentSize.height-sideLength-indent, width: sideLength, height: sideLength)
        }
    }

    func sample3(imageView: UIImageView) {
        imageView.contentMode = .scaleAspectFill
        imageView.clipsToBounds = true
        imageView.image = UIImage(named: "parent")
        imageView.drawOnCurrentImage(anotherImage: UIImage(named: "child"), mode: .addSubview) { parentSize, newImageSize in
            print("parentSize = \(parentSize)")
            print("newImageSize = \(newImageSize)")
            let sideLength:CGFloat = 90
            let indent:CGFloat = 15
            return CGRect(x: parentSize.width-sideLength-indent, y: indent, width: sideLength, height: sideLength)
        }
    }
}