rulilg rulilg - 2 years ago 471
Swift Question

Swift: UIBezierPath Stroke Animation from Center

I've been making a simple UIBezierPath animation with Swift. This path consists on creating a rounded rectangle with a colored border. The animation must be the drawing of the colored border. To do this, I've created a CAShapeLayer with a UIBezierPath(roundedRect:, cornerRadius: )` let layer = CAShapeLayer()
var viewPrueba = UIView()

override func viewDidLoad() {
// Do any additional setup after loading the view, typically from a nib.

viewPrueba = UIView(frame: CGRectMake(self.view.frame.width/2-100, self.view.frame.height/2 - 100, 200, 200))
let path = UIBezierPath(roundedRect: CGRectMake(0, 0, 200, 200), cornerRadius: 40.0)
layer.path = path.CGPath
layer.fillColor = UIColor.clearColor().CGColor
layer.strokeColor = UIColor.blueColor().CGColor
layer.strokeStart = 0.0
layer.strokeEnd = 0.0
layer.lineWidth = 4.0
layer.lineJoin = kCALineJoinRound
let tapGR = UITapGestureRecognizer(target: self, action: #selector(ViewController.anim))

func anim() {
let anim1 = CABasicAnimation(keyPath: "strokeEnd")
anim1.fromValue = 0.0
anim1.toValue = 1.0
anim1.duration = 4.0
anim1.repeatCount = 0
anim1.autoreverses = false
anim1.removedOnCompletion = false
anim1.additive = true
anim1.fillMode = kCAFillModeForwards
self.layer.addAnimation(anim1, forKey: "strokeEnd")

It works well. The only problem is that the animation starts from the top-left part of the square and not from the top-center. How can I do that?

The only thing I've found in order to achieve this is by doing it with a circle and not a rectangle, which is not what we want.

This is where the animation starts


Answer Source

CoreAnimate animated as the same order as which the UIBezierPath was drawn.
The system method

+ (instancetype)bezierPathWithRoundedRect:(CGRect)rect cornerRadius:(CGFloat)cornerRadius;     

return a UIBezierPath which was drawn from the top-left,so your animation started from the top-left.
But you can create your own UIBezierPath drawn form top-center:

func centerStartBezierPath(frame:CGRect,cornerRadius:CGFloat) -> UIBezierPath {
    let path = UIBezierPath()
    path.moveToPoint(CGPointMake(frame.width/2.0, 0))
    path.addLineToPoint(CGPointMake(frame.width-cornerRadius, 0))
    path.addArcWithCenter(CGPointMake(frame.width-cornerRadius, cornerRadius),
                          radius: cornerRadius,
                          startAngle: CGFloat(-M_PI/2),
                          endAngle: 0,
                          clockwise: true)
    path.addLineToPoint(CGPointMake(frame.width, frame.height-cornerRadius))
    path.addArcWithCenter(CGPointMake(frame.width-cornerRadius, frame.height-cornerRadius),
                          radius: cornerRadius,
                          startAngle: 0,
                          endAngle: CGFloat(M_PI/2),
                          clockwise: true)
    path.addLineToPoint(CGPointMake(cornerRadius, frame.height))
    path.addArcWithCenter(CGPointMake(cornerRadius, frame.height-cornerRadius),
                          radius: cornerRadius,
                          startAngle: CGFloat(M_PI/2),
                          endAngle: CGFloat(M_PI),
                          clockwise: true)
    path.addLineToPoint(CGPointMake(0, cornerRadius))
    path.addArcWithCenter(CGPointMake(cornerRadius, cornerRadius),
                          radius: cornerRadius,
                          startAngle: CGFloat(M_PI),
                          endAngle: CGFloat(M_PI*3/2),
                          clockwise: true)

    path.applyTransform(CGAffineTransformMakeTranslation(frame.origin.x, frame.origin.y))

    return path;

And it works like this: top-center start animation
You can also change the code,and start from any point you want.

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