Swift 3.0 - 在图像上绘图用手指查看

Question

我一直在努力使用 swift 3.0 在图像视图上画一条红线，并遇到了一些问题。正如您所猜到的，我正在使用堆栈溢出中的一些代码来帮助我进行第一次初始尝试，并且遇到了一个奇怪的错误。

当我在图像视图上拖动手指时，它确实会画一条红线，但对于每个"帧"，它会将我在屏幕上进一步绘制的所有内容都放下。所以当我画的时候，看起来我画的线正在下降，然后完全离开屏幕。

我正在寻找的是能够简单地在图像视图上绘制，而不是每帧向下移动所有内容，我希望它保持在相同的位置，类似于它在所有绘图应用程序等上的工作方式。

以下是所有代码：

@IBOutlet weak var mainImageView: UIImageView!
var lastPoint = CGPoint.zero
var fromPoint = CGPoint();
var toPoint = CGPoint.zero
var red: CGFloat = 255.0
var green: CGFloat = 0.0
var blue: CGFloat = 0.0
var brushWidth: CGFloat = 10.0
var opacity: CGFloat = 1.0
var swiped = false
override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
}
override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}
func drawLineFrom(fromPoint: CGPoint, toPoint: CGPoint)
{
    UIGraphicsBeginImageContextWithOptions(self.mainImageView.bounds.size, false, 0);
    mainImageView.image?.draw(in: CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height))
    let context = UIGraphicsGetCurrentContext()
    context?.move(to: fromPoint)
    context?.addLine(to: toPoint)
    context?.setLineCap(CGLineCap.round)
    context?.setLineWidth(brushWidth)
    context?.setStrokeColor(red: red, green: green, blue: blue, alpha: 1.0)
    context?.setBlendMode(CGBlendMode.normal)
    context?.strokePath()
    mainImageView.image = UIGraphicsGetImageFromCurrentImageContext()
    mainImageView.alpha = opacity
    UIGraphicsEndImageContext()
}
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    swiped = false;
    if let touch = touches.first {
        lastPoint = touch.location(in: self.mainImageView)
    }
}
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    swiped = true;
    if let touch = touches.first {
        let currentPoint = touch.location(in: mainImageView)
        drawLineFrom(fromPoint: lastPoint, toPoint: currentPoint)
        lastPoint = currentPoint
    }
}
override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
    if(!swiped){
        self.drawLineFrom(fromPoint: lastPoint, toPoint: lastPoint)
    }
}

谢谢你们的帮助！

Answer 1

以下代码您可以使用触摸绘制图像 (Swift 3.0(

func touchesBegan(touches: Set<NSObject>, withEvent event: UIEvent) {
swiped = false
if let touch = touches.first as? UITouch {
    lastPoint = touch.location(in: self.view)
}
 }
 func drawLineFrom(fromPoint: CGPoint, toPoint: CGPoint) {
UIGraphicsBeginImageContext(view.frame.size)
let context = UIGraphicsGetCurrentContext()
tempImageView.image?.draw(in: CGRect(x: 0, y: 0, width:     view.frame.size.width, height: view.frame.size.height))

context?.move(to: fromPoint)
context?.addLine(to: toPoint)
context?.setLineCap(CGLineCap.round)
context?.setLineWidth(brushWidth)
context?.setStrokeColor(red: red, green: green, blue: blue, alpha: 1.0)
context?.setBlendMode(CGBlendMode.normal)
context?.strokePath()

tempImageView.image = UIGraphicsGetImageFromCurrentImageContext()
tempImageView.alpha = opacity
UIGraphicsEndImageContext()
}
 func touchesMoved(touches: Set<NSObject>, withEvent event: UIEvent) {
swiped = true
if let touch = touches.first as? UITouch {
    let currentPoint = touch.location(in: view)
    drawLineFrom(fromPoint: lastPoint, toPoint: currentPoint)
    lastPoint = currentPoint
}
}

Answer 2

以下代码，您可以使用触摸绘制图像

override func touchesBegan(touches: Set<NSObject>, withEvent event: UIEvent) {

if let touch = touches.first as? UITouch{
    prevPoint1 = touch.previousLocationInView(self.view)
    prevPoint2 = touch.previousLocationInView(self.view)
    lastPoint = touch.locationInView(self.view)
}
}

 override func touchesMoved(touches: Set<NSObject>, withEvent event: UIEvent) {

if let touch = touches.first as? UITouch{
    let currentPoint = touch.locationInView(view)

    prevPoint2 = prevPoint1
    prevPoint1 = touch.previousLocationInView(self.view)


    UIGraphicsBeginImageContext(view.frame.size)
    let context = UIGraphicsGetCurrentContext()
    TempImage.image?.drawInRect(CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height))

    var mid1 = CGPointMake((prevPoint1.x + prevPoint2.x)*0.5, (prevPoint1.y + prevPoint2.y)*0.5)
    var mid2 = CGPointMake((currentPoint.x + prevPoint1.x)*0.5, (currentPoint.y + prevPoint1.y)*0.5)

    CGContextMoveToPoint(context, mid1.x, mid1.y)
    CGContextAddQuadCurveToPoint(context, prevPoint1.x, prevPoint1.y, mid2.x, mid2.y)
    //CGContextAddLineToPoint(context, toPoint.x, toPoint.y)

    CGContextSetLineCap(context, kCGLineCapRound)
    CGContextSetLineWidth(context, brushWidth)
    CGContextSetRGBStrokeColor(context, red, green,blue, 1.0)
    CGContextSetBlendMode(context, kCGBlendModeNormal)

    CGContextStrokePath(context)

    TempImage.image = UIGraphicsGetImageFromCurrentImageContext()
    TempImage.alpha = opacity
    UIGraphicsEndImageContext()

    lastPoint = currentPoint
}
 }

 override func touchesEnded(touches: Set<NSObject>, withEvent event: UIEvent) {

UIGraphicsBeginImageContext(MainImage.frame.size)
MainImage.image?.drawInRect(CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height), blendMode: kCGBlendModeNormal, alpha: 1.0)
TempImage.image?.drawInRect(CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height), blendMode: kCGBlendModeNormal, alpha: opacity)
MainImage.image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()

TempImage.image = nil
}

Answer 3

Swift 5.7.2 的解决方案

import UIKit
class DrawerViewController: UIViewController {
    
    enum Spec {
        static let brushColor = UIColor.green
        static var brushWidth: CGFloat = 10.0
        static var opacity: CGFloat = 1.0
    }
    
    var lastPoint = CGPoint.zero
    var swiped = false
        
    private var maskView = UIImageView()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // MaskView
        view.addSubview(maskView)
        maskView.translatesAutoresizingMaskIntoConstraints = false
        maskView.backgroundColor = .white
        NSLayoutConstraint.activate([
            maskView.topAnchor.constraint(equalTo: view.topAnchor),
            maskView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            maskView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            maskView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
        ])
    }
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        swiped = false
        if let touch = touches.first {
            lastPoint = touch.location(in: self.view)
        }
    }
    
    func drawLineFrom(fromPoint: CGPoint, toPoint: CGPoint) {
        UIGraphicsBeginImageContext(view.frame.size)
        let context = UIGraphicsGetCurrentContext()
        maskView.image?.draw(in: CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height))
        context?.move(to: fromPoint)
        context?.addLine(to: toPoint)
        context?.setLineCap(CGLineCap.round)
        context?.setLineWidth(Spec.brushWidth)
        context?.setStrokeColor(Spec.brushColor.cgColor)
        context?.setBlendMode(CGBlendMode.normal)
        context?.strokePath()

        maskView.image = UIGraphicsGetImageFromCurrentImageContext()
        maskView.alpha = Spec.opacity
        UIGraphicsEndImageContext()
    }
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        swiped = true
        if let touch = touches.first {
            let currentPoint = touch.location(in: view)
            drawLineFrom(fromPoint: lastPoint, toPoint: currentPoint)
            lastPoint = currentPoint
        }
    }
}