使用UIBezierPath和iOS绘制矩形填充圆动画

Question

I have this on github: https://github.com/evertoncunha/EPCSpinnerView

It does this animations:

There is a glitch in the animation, when the circle is filling and the view is resizing, and I wan't to fix that.

The glitch happens because the way I fill the circle by setting the layer corners, so it looks like a circle, and I increase the lineWidth with the animation progress, and it looks likes it's filling from outside in. From EPCDrawnIconSpinner.swift file:

let ovalPath = UIBezierPath()
ovalPath.addArc(withCenter: CGPoint(x: ovalRect.midX, y: ovalRect.midY),
                radius: ovalRect.width / 2,
                startAngle: start * CGFloat.pi/180,
                endAngle: end * CGFloat.pi/180, clockwise: true)
layer.cornerRadius = rect.size.height/2
ovalPath.lineWidth = 14 + ((frame.size.width) * progress)

Is there a better way that I can achieve this animation without doing the layer cornerRadius thing? If I could only draw this

Answer 1

I can think of two ways to get away from using cornerRadius :

1. Use a mask to round the corners, and use a shape layer to fill

You can create a CAShapeLayer of a filled circle, and with a frame set to your view's bounds, then assign it to your layer's mask property. You can animate the size of this mask as you animate the size of your view. Secondly, you will need to create an additional shape later (probably similar to your spinning circle), and do the line width animation on this layer. The mask will ensure that the line does not grow outwards, but only inwards.

2. Animate the line width and radius of the fill shape

You will need to create a circle shape layer similar to the one described in the first option, but instead of just animating the line width, you'll also need to animate the radius. For example: Let's say your view size is 40x40. Of course, at the start of the fill animation, your shape layer will also need to be 40x40. You will then animate the line width to 20pts, and animate the radius of the circle from 20pts to 10pts. A circle with a radius of 10pts and a line width of 20pts will appear to be a filled circle with a radius of 20pts.

Hope this helps.

Answer 2

I ended up with the following solution:

fileprivate func drawPathCompleted(_ ovalRect: CGRect) {

     var size: CGFloat = ovalRect.size.width

     var current = size*(1-progress)

     var pos: CGFloat = lineWidth/2

     while size > current {
       let ovalPath = UIBezierPath(ovalIn: CGRect(x: pos, y: pos, width: size, height: size))
       ovalPath.lineCapStyle = .round
       ovalPath.lineWidth = lineWidth
       ovalPath.stroke()
       let decr = lineWidth/2
       size -= decr
       pos += decr/2
     }
}

At this commit, line 243: https://github.com/evertoncunha/EPCSpinnerView/commit/87d968846d92aa97e85ff4c58b6664ad7b03f00b#diff-8dc22814328ed859a00acfcf2909854bR242