在两个圆形UIBezierPaths之间进行动画制作时的奇怪行为

Question

问题
我正在创造爆炸环效果.我正在使用多个CAShapeLayer并UIBezierPath为每个图层创建一个.初始化视图时,所有图层都有一个宽度为的路径0.触发动作时,环会为更大的路径设置动画.

如下面的演示所示,每个图层的右手边缘比每个圆形图层的其余部分的动画效果要慢.

演示

码

绘制图层:

func draw(inView view: UIView) -> CAShapeLayer {

    let shapeLayer = CAShapeLayer()

    // size.width defaults to 0
    let circlePath = UIBezierPath(arcCenter: view.center, radius: size.width / 2, startAngle: 0, endAngle: CGFloat(360.0).toRadians(), clockwise: true)

    shapeLayer.path = circlePath.CGPath
    shapeLayer.frame = view.frame

    return shapeLayer
}

更新图层

func updateAnimated(updatedOpacity: CGFloat, updatedSize: CGSize, duration: CGFloat) {

    let updatePath = UIBezierPath(arcCenter: view.center, radius: updatedSize.width / 2,
                                  startAngle: 0, endAngle: CGFloat(360).toRadians(), clockwise: true)

    let pathAnimation = CABasicAnimation(keyPath: "path")
    pathAnimation.fromValue = layer.path // the current path (initially with width 0)
    pathAnimation.toValue = updatePath.CGPath


    let opacityAnimation = CABasicAnimation(keyPath: "opacity")
    opacityAnimation.fromValue = self.opacity
    opacityAnimation.toValue = updatedOpacity


    let animationGroup = CAAnimationGroup()
    animationGroup.animations = [pathAnimation, opacityAnimation]
    animationGroup.duration = Double(duration)
    animationGroup.fillMode = kCAFillModeForwards
    animationGroup.removedOnCompletion = false

    layer.addAnimation(animationGroup, forKey: "shape_update")

    ... update variables ...

}

Answer 1

避免从路径宽度 0 开始。从 0 开始缩放非常困难，并且微小的浮点误差会放大。非常接近零的值在浮点中不是很连续（嗯......我想这实际上有点像真实的宇宙）。尝试从较大的值开始，看看可以安全地接近零。