swift - 当我在上面绘制文本时，NSImage 会调整大小

Question

我有以下代码在 NSImage 上绘制文本。但是当我将生成的图像保存到磁盘时，生成的图像被调整为较小的图像。

我做错了什么？请指教

func drawText(image :NSImage) ->NSImage
{
    let text = "Sample Text"
    let font = NSFont.boldSystemFont(ofSize: 18)
    let imageRect = CGRect(x: 0, y: 0, width: image.size.width, height: image.size.height)

    let textRect = CGRect(x: 5, y: 5, width: image.size.width - 5, height: image.size.height - 5)
    let textStyle = NSMutableParagraphStyle.default().mutableCopy() as! NSMutableParagraphStyle
    let textFontAttributes = [
        NSFontAttributeName: font,
        NSForegroundColorAttributeName: NSColor.white,
        NSParagraphStyleAttributeName: textStyle
    ]

    let im:NSImage = NSImage(size: image.size)

    let rep:NSBitmapImageRep = NSBitmapImageRep(bitmapDataPlanes: nil, pixelsWide: Int(image.size.width), pixelsHigh: Int(image.size.height), bitsPerSample: 8, samplesPerPixel: 4, hasAlpha: true, isPlanar: false, colorSpaceName: NSCalibratedRGBColorSpace, bytesPerRow: 0, bitsPerPixel: 0)!

    im.addRepresentation(rep)

    im.lockFocus()

    image.draw(in: imageRect)
    text.draw(in: textRect, withAttributes: textFontAttributes)

    im.unlockFocus()

    return im
}

Answer 1

这是一种不同的方法，使用临时 NSView 绘制图像和文本并将结果缓存在新图像中(代码为 Swift 4)。好处是你不需要处理像素

class ImageView : NSView  {

    var image : NSImage
    var text : String

    init(image: NSImage, text: String)
    {
        self.image = image
        self.text = text
        super.init(frame: NSRect(origin: NSZeroPoint, size: image.size))
    }

    required init?(coder decoder: NSCoder) { fatalError() }

    override func draw(_ dirtyRect: NSRect) {
        let font = NSFont.boldSystemFont(ofSize: 18)
        let textRect = CGRect(x: 5, y: 5, width: image.size.width - 5, height: image.size.height - 5)
        image.draw(in: dirtyRect)
        text.draw(in: textRect, withAttributes: [.font: font, .foregroundColor: NSColor.white])
    }

    var outputImage : NSImage  {
        let imageRep = bitmapImageRepForCachingDisplay(in: frame)!
        cacheDisplay(in: frame, to:imageRep)
        let tiffData = imageRep.tiffRepresentation!
        return NSImage(data : tiffData)!
    }
}

要使用它，初始化一个 View

let image = ... // get some image
let view = ImageView(image: image, text: "Sample Text")

并获取新图像

let imageWithText = view.outputImage

---

注意:

根本没有使用段落样式，但是如果你想创建一个可变的段落样式，就写

let textStyle = NSMutableParagraphStyle()