如何绘制梯形（或圆形）的文字？
假设我有一些文字：“一些归属于梯形的文字。”
我有NSAttributedString扩展名，它将UIImage返回给属性文本：
extension NSAttributedString {
func asImage() -> UIImage? {
defer {
UIGraphicsEndImageContext()
}
let size = boundingRect(with: CGSize.zero, options: [.usesLineFragmentOrigin, .truncatesLastVisibleLine], context: nil).size
UIGraphicsBeginImageContext(size)
draw(at: CGPoint.zero)
return UIGraphicsGetImageFromCurrentImageContext()
}
}
但是由于使用了boundingRect ，这个函数返回了一行文本。
------------------------------------
|Some attributed text in trapezoid.|
------------------------------------
如果我使用自定义矩形来绘制文本，它将不会有太大帮助......
UIGraphicsBeginImageContext(CGRect(x: 0, y: 0, width: 100, height: 30))
draw(at: CGPoint.zero)
...因为文本将在矩形中：
--------------
|Some attribu|
|ted text in |
|trapezoid. |
--------------
我需要的是以已知角落位置（或已知半径的圆圈）绘制梯形文本。 因此，每一行新文本都应以小偏移量开始，请参阅示例： 
所以我想看到这样的事情：
---------------
Some attribut/
ed text in /
trapezoid/
---------
我怎样才能达到这个结果？
你必须在这里下拉到CoreText级别。 好的新功能是，你将能够以任何你想要的形状绘制文本！
extension NSAttributedString {
public func draw(in path: CGPath) {
let context = UIGraphicsGetCurrentContext()!
let transform = CGAffineTransform(scaleX: +1, y: -1)
let flippedPath = CGMutablePath()
flippedPath.addPath(path, transform: transform)
let range = CFRange(location: 0, length: 0)
let framesetter = CTFramesetterCreateWithAttributedString(self)
let frame = CTFramesetterCreateFrame(framesetter, range, flippedPath, nil)
context.saveGState()
// Debug: fill path.
context.setFillColor(red: 1.0, green: 0.0, blue: 0.0, alpha: 0.5)
context.beginPath()
context.addPath(path)
context.fillPath()
context.concatenate(transform)
CTFrameDraw(frame, context)
context.restoreGState()
}
}
你可以像这样使用它：
let string = NSAttributedString(string: "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Lorem ipsum dolor sit amet, consectetur adipiscing elit.")
let bounds = CGRect(x: 0, y: 0, width: 120, height: 120)
let path = CGMutablePath()
path.move(to: CGPoint(x: 10, y: 10))
path.addLine(to: CGPoint(x: 110, y: 10))
path.addLine(to: CGPoint(x: 90, y: 110))
path.addLine(to: CGPoint(x: 30, y: 110))
path.closeSubpath()
UIGraphicsBeginImageContextWithOptions(bounds.integral.size, true, 0)
defer { UIGraphicsEndImageContext() }
let context = UIGraphicsGetCurrentContext()!
context.setFillColor(UIColor.white.cgColor)
context.fill(.infinite)
string.draw(in: path)
let image = UIGraphicsGetImageFromCurrentImageContext()!
坏消息是，这个解决方案最后并没有给你省略号。 如果你确实想要这样做，你可能需要对制版机给你的最后一行进行一些调整。
随着基督教Schnorr答案为我的目的：
import PlaygroundSupport
import UIKit
extension NSAttributedString {
/// Draws attributed string in selected CGPath.
func draw(in path: CGPath) {
guard let context = UIGraphicsGetCurrentContext() else { return }
let transform = CGAffineTransform(scaleX: 1.0, y: -1.0)
let flippedPath = CGMutablePath()
flippedPath.addPath(path, transform: transform)
let range = CFRange(location: 0, length: 0)
let framesetter = CTFramesetterCreateWithAttributedString(self)
let frame = CTFramesetterCreateFrame(framesetter, range, flippedPath, nil)
context.saveGState()
context.concatenate(transform)
CTFrameDraw(frame, context)
context.restoreGState()
}
/// Renders attributed string.
///
/// - Parameters:
/// - size: A 'CGSize' for rendering string in trapezoid.
/// - degree: A `CGFloat`, representing trapezoid angles in degrees.
/// - Returns: An optional `UIImage` with rendered string.
func asTrapezoidImage(size: CGSize, degree: CGFloat) -> UIImage? {
UIGraphicsBeginImageContextWithOptions(size, false, 0)
defer { UIGraphicsEndImageContext() }
draw(in: size.trapezoidPath(degree))
return UIGraphicsGetImageFromCurrentImageContext()
}
}
extension CGSize {
/// Converts CGSize into trapezoid CGPath.
///
/// - Parameter degree: A `CGFloat`, representing trapezoid angles in degrees.
/// - Returns: A `CGPath` with trapezoid.
func trapezoidPath(_ degree: CGFloat) -> CGPath {
var offset = height * tan(CGFloat.pi * degree / 180.0)
offset = max(0, min(width / 2.0, offset))
let path = CGMutablePath()
path.move(to: CGPoint.zero)
path.addLine(to: CGPoint(x: width, y: 0.0))
path.addLine(to: CGPoint(x: width - offset, y: height))
path.addLine(to: CGPoint(x: offset, y: height))
path.closeSubpath()
return path
}
}
使用：
let string = "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Lorem ipsum dolor sit amet, consectetur adipiscing elit."
let attributes: [NSAttributedStringKey: Any] = [
.foregroundColor: UIColor.blue,
.backgroundColor: UIColor.white,
.font: UIFont.systemFont(ofSize: 24.0)
]
let attrString = NSAttributedString(string: string, attributes: attributes)
let size = CGSize(width: 400.0, height: 120.0)
let image = attrString.asTrapezoidImage(size: size, degree: 12.0)
let imageView = UIImageView(image: image)
imageView.frame = CGRect(origin: CGPoint.zero, size: size)
PlaygroundPage.current.needsIndefiniteExecution = false
PlaygroundPage.current.liveView = imageView
说明允许从0°到90°的角度
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