ios - 以更高的分辨率将UILabel渲染为UIImage

Question

我正在使用下面的功能来将UILabel渲染为UIImage

func labelToImage(_ label: UILabel) -> UIImage {           
    UIGraphicsBeginImageContextWithOptions(CGSize(width: label.frame.size.width*10, height: label.frame.size.height*10), false, 0)
    guard let context = UIGraphicsGetCurrentContext() else { return UIImage() }
    defer { UIGraphicsEndImageContext() }
    label.layer.render(in: context)
    return UIGraphicsGetImageFromCurrentImageContext() ?? UIImage()
}

但是生成的图像分辨率太低，无法满足我的需要，我需要将其分辨率提高大约10倍。我不想缩放生成的图像，因为它将像素化。

我想缩放UILabel，然后将其渲染为图像。我已经尝试过CGAffinTransform Scale，但是没有做任何事情。

Answer 1

您需要先缩放标签的框架和字体大小，然后再将其绘制到新的图像上下文中:

func labelToImage(_ label: UILabel) -> UIImage? {
    let size = label.frame.size.applying(.init(scaleX: 10, y: 10))
    UIGraphicsBeginImageContextWithOptions(size, false, 0)
    label.frame.size = size
    label.font = label.font.withSize(label.font.pointSize * 10)
    defer { UIGraphicsEndImageContext() }
    label.draw(.init(origin: .zero, size: size))
    return UIGraphicsGetImageFromCurrentImageContext()
}

您还可以扩展UILabel以将其缩放到特定大小或百分比:

extension UILabel {
    func scaledImage(to size: CGSize) -> UIImage {
        let format = UIGraphicsImageRendererFormat()
        format.opaque = false
        let aspectRatio = size.width/frame.size.width
        frame = frame.applying(.init(scaleX: aspectRatio, y: aspectRatio))
        font = font.withSize(font.pointSize * aspectRatio)
        return UIGraphicsImageRenderer(size: size, format: format).image { _ in
            draw(.init(origin: .zero, size: size))
        }
    }
    func scaledImage(by percentage: CGFloat) -> UIImage {
        let format = UIGraphicsImageRendererFormat()
        format.opaque = false
        frame = frame.applying(.init(scaleX: percentage, y: percentage))
        font = font.withSize(font.pointSize * percentage)
        return UIGraphicsImageRenderer(size: frame.size, format: format).image { _ in
            draw(.init(origin: .zero, size: frame.size))
        }
    }
}

游乐场测试:

let label = UILabel(frame: .init(origin: .zero, size: .init(width: 200, height: 30)))
label.text = "StackOverflow"
label.scaledImage(by: 10)