调整 NSImage 的大小会改变它的起源并产生错误的结果

Question

我正在使用以下代码调整图像大小（保持纵横比）。当我尝试将大小为 2432X3648 像素的图像调整为 1800X2700 像素 输出图像原点发生偏移。

extension NSImage {   


  func resizeTo(width: CGFloat, height: CGFloat) -> NSImage {
    let ratioX = width / size.width
    let ratioY = height / size.height
    var ratio = ratioX < ratioY ? ratioX : ratioY
    let newHeight = size.height * ratio
    let newWidth = size.width * ratio
    let canvasSize = CGSize(width: newWidth, height: newHeight)
    let img = NSImage(size: canvasSize)
    img.lockFocus()
    let context = NSGraphicsContext.current()
    context?.imageInterpolation = .high
    draw(in: NSRect(origin: .zero, size: NSSize(width: newWidth,height: newHeight)), from: NSRect(origin: .zero, size: size) , operation: .copy, fraction: 1)
    img.unlockFocus()
    return img
    }


}

请查看调整大小的示例图像。我已经标记了图像。调整大小的代码在其他情况下似乎可以正常工作。请建议..

更新： @LeoDabus我已经使用了你的代码，它为输出大小1084X2086像素产生了类似的结果。我不得不稍微修改你的代码 - 只在一行上，因为它不会编译。编译器自动建议它。 NSGraphicsContext.current()?.imageInterpolation = .high

 func resizeTo(width: CGFloat, height: CGFloat) -> NSImage {
        let ratioX = width / size.width
        let ratioY = height / size.height
        let ratio = ratioX < ratioY ? ratioX : ratioY
        let newHeight = size.height * ratio
        let newWidth = size.width * ratio
        let canvasSize = CGSize(width: width, height: CGFloat(ceil(width/size.width * size.height)))
        let img = NSImage(size: canvasSize)
        img.lockFocus()
        NSGraphicsContext.current()?.imageInterpolation = .high
        draw(in: NSRect(origin: CGPoint(x: (canvasSize.width - (size.width * ratio)) / 2, y: (canvasSize.height - (size.height * ratio)) / 2), size: NSSize(width: newWidth,height: newHeight)), from: NSRect(origin: .zero, size: size), operation: .copy, fraction: 1)
        img.unlockFocus()
        return img

}

Answer 1

真正的错误只是画布大小应该使用新的宽度和高度：

extension NSImage {
    func resizedTo(width: CGFloat, height: CGFloat) -> NSImage {
        let ratio = min(canvas.width/size.width, canvas.height/size.height)
        let canvasSize = NSSize(width: size.width * ratio, height: size.height * ratio)
        let img = NSImage(size: canvasSize)
        img.lockFocus()
        NSGraphicsContext.current?.imageInterpolation = .high
        draw(in: NSRect(origin: CGPoint(x: (canvasSize.width - (size.width * ratio)) / 2, y: (canvasSize.height - (size.height * ratio)) / 2), size: canvasSize), from: NSRect(origin: .zero, size: size), operation: .copy, fraction: 1)
        img.unlockFocus()
        return img
    }
}