Cocoa：在Swift中保存時捕獲螢屏并縮放影像

下面的代碼我用來在 macOS 應用程式中捕獲螢屏，

let img = CGDisplayCreateImage(CGMainDisplayID())

guard let destination = FileManager.default.urls(for: .downloadsDirectory,
    in: .userDomainMask).first?.appendingPathComponent("shot.jpg", isDirectory: false)
else {
    print("Unable to save captured image!")
    return
}
            
let properties: CFDictionary = [
    kCGImagePropertyPixelWidth: "900",
    kCGImagePropertyPixelHeight: "380"
] as CFDictionary
            
if let dest = CGImageDestinationCreateWithURL(destination as CFURL, kUTTypeJPEG, 1, properties) {
    CGImageDestinationAddImage(dest, img!, properties)
    CGImageDestinationFinalize(dest)
}
else {
    print("Unable to create captured image to the destination!")
}

我必須在保存時將影像縮放到特定大小。所以，我使用CFDictionary了width, heigh影像的屬性。但似乎我做錯了。請幫我找出正確的解決方案。謝謝！

uj5u.com熱心網友回復：

首先，您不能使用CGImageDestinationCreateWithURLor調整大小CGImageDestinationAddImage。如果您查看此處和此處的檔案，您會注意到既不支持kCGImagePropertyPixelWidth也不kCGImagePropertyPixelHeight支持。

您將需要手動調整大小。如果您覺得它有幫助，您可以使用此工具或對其進行修改。它支持填充（拉伸）和適合（在保持原始縱橫比的同時縮放）內容模式。如果您指定.fit它將使繪圖在結果影像中居中。如果您指定.fill，它將填充整個空間，拉伸它需要的任何尺寸。

enum ImageResizer {

    enum ContentMode {
        case fill
        case fit
    }

    enum Error: Swift.Error {
        case badOriginal
        case resizeFailed
    }

    static func resize(_ source: CGImage, to targetSize: CGSize, mode: ContentMode) throws -> CGImage {

        let context = CGContext(
            data: nil,
            width: Int(targetSize.width),
            height: Int(targetSize.height),
            bitsPerComponent: source.bitsPerComponent,
            bytesPerRow: 0,
            space: source.colorSpace ?? CGColorSpace(name: CGColorSpace.sRGB)!,
            bitmapInfo: source.bitmapInfo.rawValue
        )

        guard let context = context else {
            throw Error.badOriginal
        }

        let drawingSize: CGSize
        switch mode {
        case .fill:
            drawingSize = targetSize
        case .fit:
            drawingSize = CGSize(width: source.width, height: source.height)
                .scaledToFit(target: targetSize)
        }

        let drawRect = CGRect(origin: .zero, size: targetSize)
            .makeCenteredRect(withSize: drawingSize)

        context.interpolationQuality = .high
        context.draw(source, in: drawRect)

        guard let result = context.makeImage() else {
            throw Error.resizeFailed
        }

        return result
    }
}

ImageResizer 依賴于這些 CG 擴展來縮放源影像和居中縮放影像：

extension CGSize {

    var maxDimension: CGFloat {
        Swift.max(width, height)
    }

    var minDimension: CGFloat {
        Swift.min(width, height)
    }

    func scaled(by scalar: CGFloat) -> CGSize {
        CGSize(width: width * scalar, height: height * scalar)
    }

    func scaleFactors(to target: CGSize) -> CGSize {
        CGSize(
            width: target.width / width,
            height: target.height / height
        )
    }

    func scaledToFit(target: CGSize) -> CGSize {
        return scaled(by: scaleFactors(to: target).minDimension)
    }
}

extension CGRect {
    func makeCenteredRect(withSize size: CGSize) -> CGRect {
        let origin = CGPoint(
            x: midX - size.width / 2.0,
            y: midY - size.height / 2.0
        )
        return CGRect(origin: origin, size: size)
    }
}

此外，如果您要保存到.downloadsDirectory.

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