Moving an object along a curve in iPhone development

Question

I wanted to animate an image object by moving it along a particular curve. It is not a general or random curve but rather a curve which follows a particular path on screen.

Currently, Im manually specifying the list of x and y co-ordinates of the path along which i want the image object to move by setting its frame each time. This is a laborious process in the sense that im setting the specific x and y coordinates of the path and moving the image along it. Is there a more efficient way to do this?

Is there a way that i can specify,say, just about 15 - 20 points and have a curve traced along those to move the object? Any other way to acheive this? Any help would be much appreciated. Thanks.

Answer 1

You could use a combination of UIBezierPath and CAKeyFrameAnimation. I found a very useful blog post dealing with this subject.

http://oleb.net/blog/2010/12/animating-drawing-of-cgpath-with-cashapelayer/

Here's a simplified version of what I used (it just animates the drawing of a square):

UIBezierPath *customPath = [UIBezierPath bezierPath];
[customPath moveToPoint:CGPointMake(100,100)];
[customPath addLineToPoint:CGPointMake(200,100)];
[customPath addLineToPoint:CGPointMake(200,200)];
[customPath addLineToPoint:CGPointMake(100,200)];
[customPath addLineToPoint:CGPointMake(100,100)];

UIImage *movingImage = [UIImage imageNamed:@"foo.png"];
CALayer *movingLayer = [CALayer layer];
movingLayer.contents = (id)movingImage.CGImage;
movingLayer.anchorPoint = CGPointZero;
movingLayer.frame = CGRectMake(0.0f, 0.0f, movingImage.size.width, movingImage.size.height);
[self.view.layer addSublayer:movingLayer];

CAKeyframeAnimation *pathAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
pathAnimation.duration = 4.0f;
pathAnimation.path = customPath.CGPath;
pathAnimation.calculationMode = kCAAnimationLinear;
[movingLayer addAnimation:pathAnimation forKey:@"movingAnimation"];

Answer 2

In Swift-3 version of @Jilouc :-

    override func viewDidLoad() {
        super.viewDidLoad()
        addAdditiveAnimation()
        initiateAnimation()
     }

    //curve which follows a particular path  
    func pathToTrace() -> UIBezierPath {
            let path =  UIBezierPath(ovalIn: CGRect(x: 120  , y: 120, width: 100, height: 100))
            let shapeLayer = CAShapeLayer()
            shapeLayer.path = path.cgPath
            shapeLayer.strokeColor = UIColor.red.cgColor
            shapeLayer.lineWidth = 1.0
            self.view.layer.addSublayer(shapeLayer)
            return path
        }

func addAdditiveAnimation() {
        let movement = CAKeyframeAnimation(keyPath: "position")
        movement.path = pathToTrace().cgPath
        movement.duration = 5
        movement.repeatCount = HUGE
        movement.calculationMode = kCAAnimationPaced
        movement.timingFunctions = [CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseOut)]
        self.movement = movement
}

func createLayer() -> CALayer {
        let layer = CALayer()
        let image = UIImage(named: "launch.png")
        layer.frame = CGRect(x: 0 , y: 0, width: (image?.size.width),height: (image?.size.height))
        layer.position = CGPoint(x: 5, y: 5)
        layer.contents = image?.cgImage
        layer.anchorPoint =  .zero
        layer.backgroundColor =  UIColor.red.cgColor
        //layer.cornerRadius =  5
        self.view.layer.addSublayer(layer)
        return layer
    }

func initiateAnimation() {
        let layer = createLayer()
        layer.add(self.movement, forKey: "Object Movement")
     }

Github Demo