Swift iOSの場合、円形パスに沿ってテキストを描画します

Question

_Swift2_ for _iOS9_を使用して、円の端に単純な単一行の文字列を描画する方法に関する最新のヘルプ/ヒントを探しています。古いObjCフラグメントを含むかなり古い例があり、_OS X_のみに制限されていることがよくあります。これは、カスタムUIViewサブクラスのdrawRect()メソッド内のiOSでも可能ですか？

Answer 1

「何を試してみましたか？」と言っていましたが、金曜日の午後であり、早めに仕事を辞めたので、古いObjCコードを翻訳する機会を得ました。ここでは、遊び場に適しています。 UIViewに配置するのは簡単です。

スイフト2
Swift 3＆Swift 4つの更新...

import UIKit

func centreArcPerpendicularText(str: String, context: CGContextRef, radius r: CGFloat, angle theta: CGFloat, colour c: UIColor, font: UIFont, clockwise: Bool){
    // *******************************************************
    // This draws the String str around an arc of radius r,
    // with the text centred at polar angle theta
    // *******************************************************

    let l = str.characters.count
    let attributes = [NSFontAttributeName: font]

    var characters: [String] = [] // This will be 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 {
        characters += [String(str[str.startIndex.advancedBy(i)])]
        arcs += [chordToArc(characters[i].sizeWithAttributes(attributes).width, radius: r)]
        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(M_PI_2) : CGFloat(M_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 = theta - direction * totalArc / 2

    for i in 0 ..< l {
        thetaI += direction * arcs[i] / 2
        // Call centerText with each character in turn.
        // Remember to add +/-90º to the slantAngle otherwise
        // the characters will "stack" round the arc rather than "text flow"
        centreText(characters[i], context: context, radius: r, angle: thetaI, colour: c, font: font, 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))
}

func centreText(str: String, context: CGContextRef, radius r:CGFloat, angle theta: CGFloat, colour c: UIColor, font: UIFont, slantAngle: CGFloat) {
    // *******************************************************
    // This draws the String str centred at the position
    // specified by the polar coordinates (r, theta)
    // i.e. the x= r * cos(theta) y= r * sin(theta)
    // and rotated by the angle slantAngle
    // *******************************************************

    // Set the text attributes
    let attributes = [NSForegroundColorAttributeName: c,
        NSFontAttributeName: font]
    // Save the context
    CGContextSaveGState(context)
    // Undo the inversion of the Y-axis (or the text goes backwards!)
    CGContextScaleCTM(context, 1, -1)
    // Move the Origin to the centre of the text (negating the y-axis manually)
    CGContextTranslateCTM(context, r * cos(theta), -(r * sin(theta)))
    // Rotate the coordinate system
    CGContextRotateCTM(context, -slantAngle)
    // Calculate the width of the text
    let offset = str.sizeWithAttributes(attributes)
    // Move the Origin by half the size of the text
    CGContextTranslateCTM (context, -offset.width / 2, -offset.height / 2) // Move the Origin to the centre of the text (negating the y-axis manually)
    // Draw the text
    str.drawAtPoint(CGPointZero, withAttributes: attributes)
    // Restore the context
    CGContextRestoreGState(context)
}

// *******************************************************
// Playground code to test
// *******************************************************
let size = CGSize(width: 256, height: 256)

UIGraphicsBeginImageContextWithOptions(size, true, 0.0)
let context = UIGraphicsGetCurrentContext()!
// *******************************************************************
// Scale & translate the context to have 0,0
// at the centre of the screen maths convention
// Obviously change your Origin to suit...
// *******************************************************************
CGContextTranslateCTM (context, size.width / 2, size.height / 2)
CGContextScaleCTM (context, 1, -1)

centreArcPerpendicularText("Hello round world", context: context, radius: 100, angle: 0, colour: UIColor.redColor(), font: UIFont.systemFontOfSize(16), clockwise: true)
centreArcPerpendicularText("Anticlockwise", context: context, radius: 100, angle: CGFloat(-M_PI_2), colour: UIColor.redColor(), font: UIFont.systemFontOfSize(16), clockwise: false)
centreText("Hello flat world", context: context, radius: 0, angle: 0 , colour: UIColor.yellowColor(), font: UIFont.systemFontOfSize(16), slantAngle: CGFloat(M_PI_4))


let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()

出力は：

更新 時計回り/反時計回りおよび直線の例を追加しました。

更新Swift 3

func centreArcPerpendicular(text str: String, context: CGContext, radius r: CGFloat, angle theta: CGFloat, colour c: UIColor, font: UIFont, clockwise: Bool){
    // *******************************************************
    // This draws the String str around an arc of radius r,
    // with the text centred at polar angle theta
    // *******************************************************

    let l = str.characters.count
    let attributes = [NSFontAttributeName: 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: r)]
        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(M_PI_2) : CGFloat(M_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 = theta - direction * totalArc / 2

    for i in 0 ..< l {
        thetaI += direction * arcs[i] / 2
        // Call centerText 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: r, angle: thetaI, colour: c, font: font, 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))
}

func centre(text str: String, context: CGContext, radius r:CGFloat, angle theta: CGFloat, colour c: UIColor, font: UIFont, slantAngle: CGFloat) {
    // *******************************************************
    // This draws the String str centred at the position
    // specified by the polar coordinates (r, theta)
    // i.e. the x= r * cos(theta) y= r * sin(theta)
    // and rotated by the angle slantAngle
    // *******************************************************

    // Set the text attributes
    let attributes = [NSForegroundColorAttributeName: c,
                      NSFontAttributeName: font]
    // Save the context
    context.saveGState()
    // Undo the inversion of the Y-axis (or the text goes backwards!)
    context.scaleBy(x: 1, y: -1)
    // 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()
}

// *******************************************************
// Playground code to test
// *******************************************************
let size = CGSize(width: 256, height: 256)

UIGraphicsBeginImageContextWithOptions(size, true, 0.0)
let context = UIGraphicsGetCurrentContext()!
// *******************************************************************
// Scale & translate the context to have 0,0
// at the centre of the screen maths convention
// Obviously change your Origin to suit...
// *******************************************************************
context.translateBy (x: size.width / 2, y: size.height / 2)
context.scaleBy (x: 1, y: -1)

centreArcPerpendicular(text: "Hello round world", context: context, radius: 100, angle: 0, colour: UIColor.red, font: UIFont.systemFont(ofSize: 16), clockwise: true)
centreArcPerpendicular(text: "Anticlockwise", context: context, radius: 100, angle: CGFloat(-M_PI_2), colour: UIColor.red, font: UIFont.systemFont(ofSize: 16), clockwise: false)
centre(text: "Hello flat world", context: context, radius: 0, angle: 0 , colour: UIColor.yellow, font: UIFont.systemFont(ofSize: 16), slantAngle: CGFloat(M_PI_4))


let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()

スイフト4
さらに小さな変更、今回はM_PIの廃止、.charactersのStringの放棄、.size(withAttributes...のパラメーターラベルの変更、およびテキスト属性の変更を修正しました。 NSAttributedStringKey enum ...

import UIKit

func centreArcPerpendicular(text str: String, context: CGContext, radius r: CGFloat, angle theta: CGFloat, colour c: UIColor, font: UIFont, clockwise: Bool){
    // *******************************************************
    // This draws the String str around an arc of radius r,
    // with the text centred at polar angle theta
    // *******************************************************

    let characters: [String] = str.map { String($0) } // An array of single character strings, each character in str
    let l = characters.count
    let attributes = [NSAttributedStringKey.font: font]

    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(withAttributes: attributes).width, radius: r)]
        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: CGFloat = clockwise ? -.pi / 2 : .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 = theta - direction * totalArc / 2

    for i in 0 ..< l {
        thetaI += direction * arcs[i] / 2
        // Call centerText 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: r, angle: thetaI, colour: c, font: font, 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))
}

func centre(text str: String, context: CGContext, radius r: CGFloat, angle theta: CGFloat, colour c: UIColor, font: UIFont, slantAngle: CGFloat) {
    // *******************************************************
    // This draws the String str centred at the position
    // specified by the polar coordinates (r, theta)
    // i.e. the x= r * cos(theta) y= r * sin(theta)
    // and rotated by the angle slantAngle
    // *******************************************************

    // Set the text attributes
    let attributes = [NSAttributedStringKey.foregroundColor: c, NSAttributedStringKey.font: font]
    //let attributes = [NSForegroundColorAttributeName: c, NSFontAttributeName: font]
    // Save the context
    context.saveGState()
    // Undo the inversion of the Y-axis (or the text goes backwards!)
    context.scaleBy(x: 1, y: -1)
    // 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(withAttributes: 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()
}

// *******************************************************
// Playground code to test
// *******************************************************
let size = CGSize(width: 256, height: 256)

UIGraphicsBeginImageContextWithOptions(size, true, 0.0)
let context = UIGraphicsGetCurrentContext()!
// *******************************************************************
// Scale & translate the context to have 0,0
// at the centre of the screen maths convention
// Obviously change your Origin to suit...
// *******************************************************************
context.translateBy (x: size.width / 2, y: size.height / 2)
context.scaleBy(x: 1, y: -1)

centreArcPerpendicular(text: "Hello round ???? world", context: context, radius: 100, angle: 0, colour: UIColor.red, font: UIFont.systemFont(ofSize: 16), clockwise: true)
centreArcPerpendicular(text: "Anticlockwise", context: context, radius: 100, angle: CGFloat(-M_PI_2), colour: UIColor.red, font: UIFont.systemFont(ofSize: 16), clockwise: false)
centre(text: "Hello flat world", context: context, radius: 0, angle: 0 , colour: UIColor.yellow, font: UIFont.systemFont(ofSize: 16), slantAngle: .pi / 4)


let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()

UIViewでの使用を表示するための更新

コメンテーター@RitvikUpadhyayaは、UIViewでこれを行う方法を尋ねます-初心者には明らかですが、初心者にはおそらくわかりません。秘Theは、UIGraphicsGetCurrentContextを使用して正しいコンテキストを取得することですwithoutUIGraphicsBeginImageContextWithOptionsの呼び出し（UIViewのコンテキストをcurrentコンテキストとしてオーバーライドします）-したがって、UIViewは次のようになります。

class MyView: UIView {
    override func draw(_ rect: CGRect) {
        guard let context = UIGraphicsGetCurrentContext() else { return }
        let size = self.bounds.size

        context.translateBy (x: size.width / 2, y: size.height / 2)
        context.scaleBy (x: 1, y: -1)

        centreArcPerpendicular(text: "Hello round world", context: context, radius: 100, angle: 0, colour: UIColor.red, font: UIFont.systemFont(ofSize: 16), clockwise: true)
        centreArcPerpendicular(text: "Anticlockwise", context: context, radius: 100, angle: CGFloat(-M_PI_2), colour: UIColor.red, font: UIFont.systemFont(ofSize: 16), clockwise: false)
        centre(text: "Hello flat world", context: context, radius: 0, angle: 0 , colour: UIColor.yellow, font: UIFont.systemFont(ofSize: 16), slantAngle: CGFloat(M_PI_4))
    }
}

Answer 2

円形パス上のUILabelの@IBDesignable

まず第一に、@ GrimxnがTHE MANであることに全員が同意できると思います！彼の解決策はおしりを蹴る。私は彼の作品を取り上げ、それをストーリーボードで設定および編集できるカスタムUILabelコントロールにリファクタリングしました。あなたが私のビデオを見るなら、あなたは私がこのことをするのがどれだけ大好きか知っています！ ????

カスタムUILabel用のSwift 3コード

import UIKit

@IBDesignable
class UILabelX: UILabel {
    // *******************************************************
    // DEFINITIONS (Because I'm not brilliant and I'll forget most this tomorrow.)
    // Radius: A straight line from the center to the circumference of a circle.
    // Circumference: The distance around the Edge (outer line) the circle.
    // Arc: A part of the circumference of a circle. Like a length or section of the circumference.
    // Theta: A label or name that represents an angle.
    // Subtend: A letter has a width. If you put the letter on the circumference, the letter's width
    //          gives you an arc. So now that you have an arc (a length on the circumference) you can
    //          use that to get an angle. You get an angle when you draw a line from the center of the
    //          circle to each end point of your arc. So "subtend" means to get an angle from an arc.
    // Chord: A line segment connecting two points on a curve. If you have an arc then there is a
    //          start point and an end point. If you draw a straight line from start point to end point
    //          then you have a "chord".
    // sin: (Super simple/incomplete definition) Or "sine" takes an angle in degrees and gives you a number.
    // asin: Or "asine" takes a number and gives you an angle in degrees. Opposite of sine.
    //          More complete definition: http://www.mathsisfun.com/sine-cosine-tangent.html
    // cosine: Also takes an angle in degrees and gives you another number from using the two radiuses (radii).
    // *******************************************************

    @IBInspectable var angle: CGFloat = 1.6
    @IBInspectable var clockwise: Bool = true

    override func draw(_ rect: CGRect) {
        centreArcPerpendicular()
    }

    /**
     This draws the self.text around an arc of radius r,
     with the text centred at polar angle theta
     */
    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(M_PI_2) : CGFloat(M_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)
     i.e. 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
    }
}

ストーリーボードでの使用例

行った変更

• ラベルから直接取得できるパラメーターを削除しました。
• 私は確かに三角法で最も賢くなく、私の年齢でたくさん忘れていたので、関連するすべての定義を含めて、@ Grimxnの輝きを理解し始めました。
• angleおよびclockwise設定は、Attributes Inspectorで調整できるプロパティになりました。
• ここで、ラベルのサイズから半径を作成します。
• 関数のコメントの一部を標準形式で配置すると、OPTION + CLICK関数が表示されるポップアップが表示されます。

私が見た問題

上記を編集して改善することをお勧めします。

• 理由はわかりませんが、ドキュメントのアウトラインでラベルが背後にあるにもかかわらず、ラベルが他のコントロール上でレンダリングし続けることがありました。

Answer 3

常に同じ実装ですが、Swift 4に合わせて調整されています

import UIKit

@IBDesignable
class CircularLabel: UILabel {
    // *******************************************************
    // DEFINITIONS (Because I'm not brilliant and I'll forget most this tomorrow.)
    // Radius: A straight line from the center to the circumference of a circle.
    // Circumference: The distance around the Edge (outer line) the circle.
    // Arc: A part of the circumference of a circle. Like a length or section of the circumference.
    // Theta: A label or name that represents an angle.
    // Subtend: A letter has a width. If you put the letter on the circumference, the letter's width
    //          gives you an arc. So now that you have an arc (a length on the circumference) you can
    //          use that to get an angle. You get an angle when you draw a line from the center of the
    //          circle to each end point of your arc. So "subtend" means to get an angle from an arc.
    // Chord: A line segment connecting two points on a curve. If you have an arc then there is a
    //          start point and an end point. If you draw a straight line from start point to end point
    //          then you have a "chord".
    // sin: (Super simple/incomplete definition) Or "sine" takes an angle in degrees and gives you a number.
    // asin: Or "asine" takes a number and gives you an angle in degrees. Opposite of sine.
    //          More complete definition: http://www.mathsisfun.com/sine-cosine-tangent.html
    // cosine: Also takes an angle in degrees and gives you another number from using the two radiuses (radii).
    // *******************************************************

    @IBInspectable var angle: CGFloat = 1.6
    @IBInspectable var clockwise: Bool = true

    override func draw(_ rect: CGRect) {
        centreArcPerpendicular()
    }
    /**
    This draws the self.text around an arc of radius r,
    with the text centred at polar angle theta
    */
    func centreArcPerpendicular() {
        guard let context = UIGraphicsGetCurrentContext() else { return }
        let string = text ?? ""
        let size   = bounds.size
        context.translateBy(x: size.width / 2, y: size.height / 2)

        let radius = getRadiusForLabel()
        let l = string.count
        let attributes = [NSAttributedStringKey.font : self.font!]

        let characters: [String] = string.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(withAttributes: 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)
    i.e. 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 : [NSAttributedStringKey : Any] = [
            NSAttributedStringKey.foregroundColor: textColor!,
            NSAttributedStringKey.font: font!
            ]
        // 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(withAttributes: 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(bounds.size.height, bounds.size.width)
        let heightOfFont = text?.size(withAttributes: [NSAttributedStringKey.font: self.font]).height ?? 0

        // Dividing the smallestWidthOrHeight by 2 gives us the radius for the circle.
        return (smallestWidthOrHeight/2) - heightOfFont + 5
    }
}

Answer 4

@IBDesignable for UILabel for Circular Path for Swift 2

@Grimxnと@ mark-moeykensの両方に、本当に素晴らしい仕事をしてくれてありがとう。 Markの作業に小さなリファクタリングを行ったので、Swift 3.に更新するのに時間がかからないプロジェクトで使用できるようになりました。役に立ちました。

カスタムUILabel用のSwift 2コード

import UIKit

@IBDesignable
class ArcUILabel: UILabel
{
    // *******************************************************
    // DEFINITIONS (Because I'm not brilliant and I'll forget most this tomorrow.)
    // Radius: A straight line from the center to the circumference of a circle.
    // Circumference: The distance around the Edge (outer line) the circle.
    // Arc: A part of the circumference of a circle. Like a length or section of the circumference.
    // Theta: A label or name that represents an angle.
    // Subtend: A letter has a width. If you put the letter on the circumference, the letter's width
    //          gives you an arc. So now that you have an arc (a length on the circumference) you can
    //          use that to get an angle. You get an angle when you draw a line from the center of the
    //          circle to each end point of your arc. So "subtend" means to get an angle from an arc.
    // Chord: A line segment connecting two points on a curve. If you have an arc then there is a
    //          start point and an end point. If you draw a straight line from start point to end point
    //          then you have a "chord".
    // sin: (Super simple/incomplete definition) Or "sine" takes an angle in degrees and gives you a number.
    // asin: Or "asine" takes a number and gives you an angle in degrees. Opposite of sine.
    //          More complete definition: http://www.mathsisfun.com/sine-cosine-tangent.html
    // cosine: Also takes an angle in degrees and gives you another number from using the two radiuses (radii).
    // *******************************************************

    @IBInspectable var angle: CGFloat = 1.6
    @IBInspectable var clockwise: Bool = true

    override func drawRect(rect: CGRect)
    {
        centreArcPerpendicular()
    }

    /**
     This draws the self.text around an arc of radius r,
     with the text centred at polar angle theta
     */
    func centreArcPerpendicular() {
        guard let context = UIGraphicsGetCurrentContext() else { return }
        let str = self.text ?? ""
        let size = self.bounds.size
        CGContextTranslateCTM(context, size.width / 2, size.height / 2)

        let radius = getRadiusForLabel()
        let l = str.characters.count
        let attributes: [String : AnyObject] = [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].sizeWithAttributes(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(M_PI_2) : CGFloat(M_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)
     i.e. 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 : AnyObject]
        // Save the context
        CGContextSaveGState(context)
        // Move the Origin to the centre of the text (negating the y-axis manually)
        CGContextTranslateCTM(context, r * cos(theta), -(r * sin(theta)))
        // Rotate the coordinate system
        CGContextRotateCTM(context, -slantAngle)

        // Calculate the width of the text
        let offset: CGSize = str.sizeWithAttributes(attributes)
        // Move the Origin by half the size of the text
        CGContextTranslateCTM(context, -offset.width / 2, -offset.height / 2)

        // Draw the text
        let txtStr = NSString(string: str)
        txtStr.drawAtPoint(CGPoint(x: 0, y: 0), withAttributes: attributes)

        // Restore the context
        CGContextRestoreGState(context)
    }

    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?.sizeWithAttributes([NSFontAttributeName: self.font]).height ?? 0

        // Dividing the smallestWidthOrHeight by 2 gives us the radius for the circle.
        return (smallestWidthOrHeight/2) - heightOfFont + 5
    }
}