Moving an object along a curve in iPhone development - iphone

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