弯曲的文本代码修改

我有这个UILabel子类，创build一个文本在一个圆圈。
我有3个主要的问题： 在Swift for iOS中沿着圆形path绘制文本

1. 我无法弄清楚，如何dynamic地将半径设置为一个圆弧，而不是一个完整的圆（现在是基于最小宽度/高度的半径）。

2. dynamic地将其重新变成平面文本。 （=实时设置半径0）

3. 你不能label.sizeToFit() ，它label.sizeToFit()了一切。

所以我需要创build一些属性半径，可以在旅途中改变它。

 var angle: CGFloat = 1.6 var clockwise: Bool = true var curveRadius:CGFloat = 32.0 override func draw(_ rect: CGRect) { centreArcPerpendicular() } func centreArcPerpendicular() { guard let context = UIGraphicsGetCurrentContext() else { return } let str = self.text ?? "" let size = self.bounds.size context.translateBy(x: size.width / 2, y: size.height / 2) let radius = getRadiusForLabel() let l = str.characters.count let attributes: [String : Any] = [NSFontAttributeName: self.font] let characters: [String] = str.characters.map { String($0) } // An array of single character strings, each character in str var arcs: [CGFloat] = [] // This will be the arcs subtended by each character var totalArc: CGFloat = 0 // ... and the total arc subtended by the string // Calculate the arc subtended by each letter and their total for i in 0 ..< l { arcs += [chordToArc(characters[i].size(attributes: attributes).width, radius: radius)] totalArc += arcs[i] } // Are we writing clockwise (right way up at 12 o'clock, upside down at 6 o'clock) // or anti-clockwise (right way up at 6 o'clock)? let direction: CGFloat = clockwise ? -1 : 1 let slantCorrection = clockwise ? -CGFloat.pi / 2 : CGFloat.pi / 2 // The centre of the first character will then be at // thetaI = theta - totalArc / 2 + arcs[0] / 2 // But we add the last term inside the loop var thetaI = angle - direction * totalArc / 2 for i in 0 ..< l { thetaI += direction * arcs[i] / 2 // Call centre with each character in turn. // Remember to add +/-90º to the slantAngle otherwise // the characters will "stack" round the arc rather than "text flow" centre(text: characters[i], context: context, radius: radius, angle: thetaI, slantAngle: thetaI + slantCorrection) // The centre of the next character will then be at // thetaI = thetaI + arcs[i] / 2 + arcs[i + 1] / 2 // but again we leave the last term to the start of the next loop... thetaI += direction * arcs[i] / 2 } } func chordToArc(_ chord: CGFloat, radius: CGFloat) -> CGFloat { // ******************************************************* // Simple geometry // ******************************************************* return 2 * asin(chord / (2 * radius)) } /** This draws the String str centred at the position specified by the polar coordinates (r, theta) ie the x= r * cos(theta) y= r * sin(theta) and rotated by the angle slantAngle */ func centre(text str: String, context: CGContext, radius r:CGFloat, angle theta: CGFloat, slantAngle: CGFloat) { // Set the text attributes let attributes = [NSForegroundColorAttributeName: self.textColor, NSFontAttributeName: self.font] as [String : Any] // Save the context context.saveGState() // Move the origin to the centre of the text (negating the y-axis manually) context.translateBy(x: r * cos(theta), y: -(r * sin(theta))) // Rotate the coordinate system context.rotate(by: -slantAngle) // Calculate the width of the text let offset = str.size(attributes: attributes) // Move the origin by half the size of the text context.translateBy(x: -offset.width / 2, y: -offset.height / 2) // Move the origin to the centre of the text (negating the y-axis manually) // Draw the text str.draw(at: CGPoint(x: 0, y: 0), withAttributes: attributes) // Restore the context context.restoreGState() } func getRadiusForLabel() -> CGFloat { // Imagine the bounds of this label will have a circle inside it. // The circle will be as big as the smallest width or height of this label. // But we need to fit the size of the font on the circle so make the circle a little // smaller so the text does not get drawn outside the bounds of the circle. let smallestWidthOrHeight = min(self.bounds.size.height, self.bounds.size.width) let heightOfFont = self.text?.size(attributes: [NSFontAttributeName: self.font]).height ?? 0 // Dividing the smallestWidthOrHeight by 2 gives us the radius for the circle. return (smallestWidthOrHeight/2) - heightOfFont + 5 } [1]: https://stackoverflow.com/questions/32771864/draw-text-along-circular-path-in-swift-for-ios/32785652