ios - 如何逐像素创建图像

Question

我想在 swift 3 中逐像素创建一个 UIImage

我搜索过但找不到真正有效的代码

所以让我解释一下，我有一个包含字符的数组

var array = ["w", "x", "y", "x", "y", "y", "y", "x", "x", "x", "w", "x", "y", "w", "y"] //there will be like 26 millions of those

如果是w，像素的颜色将为蓝色

如果是x，像素的颜色会是红色

如果是y，像素的颜色将为绿色

如果是v，像素的颜色将为黑色

我想用这些字符创建图像并将其存储在照片中

有什么想法吗？？

感谢您的回答

Answer 1

您可以创建一个 CGContext，然后检索该图像的 data 缓冲区，然后用与您的字符串值相对应的值填充该缓冲区:

func createImage(width: Int, height: Int, from array: [String], completionHandler: @escaping (UIImage?, String?) -> Void) {
    DispatchQueue.global(qos: .utility).async {
        let colorSpace       = CGColorSpaceCreateDeviceRGB()
        let bytesPerPixel    = 4
        let bitsPerComponent = 8
        let bytesPerRow      = bytesPerPixel * width
        let bitmapInfo       = RGBA32.bitmapInfo

        guard array.count == width * height else {
            completionHandler(nil, "Array size \(array.count) is incorrect given dimensions \(width) x \(height)")
            return
        }

        guard let context = CGContext(data: nil, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo) else {
            completionHandler(nil, "unable to create context")
            return
        }

        guard let buffer = context.data else {
            completionHandler(nil, "unable to get context data")
            return
        }

        let pixelBuffer = buffer.bindMemory(to: RGBA32.self, capacity: width * height)

        for (index, string) in array.enumerated() {
            switch string {
            case "w": pixelBuffer[index] = .blue
            case "x": pixelBuffer[index] = .red
            case "y": pixelBuffer[index] = .green
            case "v": pixelBuffer[index] = .black
            default: completionHandler(nil, "Unexpected value: \(string)"); return
            }
        }

        let cgImage = context.makeImage()!

        let image = UIImage(cgImage: cgImage)

        // or
        //
        // let image = UIImage(cgImage: cgImage, scale: UIScreen.main.scale, orientation: .up)

        completionHandler(image, nil)
    }

}

如果有 2600 万像素，您可能希望使其异步以避免阻塞主队列。

顺便说一句，上面使用了这个struct:

struct RGBA32: Equatable {
    private var color: UInt32

    var redComponent: UInt8 {
        return UInt8((color >> 24) & 255)
    }

    var greenComponent: UInt8 {
        return UInt8((color >> 16) & 255)
    }

    var blueComponent: UInt8 {
        return UInt8((color >> 8) & 255)
    }

    var alphaComponent: UInt8 {
        return UInt8((color >> 0) & 255)
    }

    init(red: UInt8, green: UInt8, blue: UInt8, alpha: UInt8) {
        color = (UInt32(red) << 24) | (UInt32(green) << 16) | (UInt32(blue) << 8) | (UInt32(alpha) << 0)
    }

    static let bitmapInfo = CGImageAlphaInfo.premultipliedLast.rawValue | CGBitmapInfo.byteOrder32Little.rawValue

    static func ==(lhs: RGBA32, rhs: RGBA32) -> Bool {
        return lhs.color == rhs.color
    }

    static let black = RGBA32(red: 0, green: 0, blue: 0, alpha: 255)
    static let red   = RGBA32(red: 255, green: 0, blue: 0, alpha: 255)
    static let green = RGBA32(red: 0, green: 255, blue: 0, alpha: 255)
    static let blue  = RGBA32(red: 0, green: 0, blue: 255, alpha: 255)
}

要保存图像，您可以:

createImage(width: width, height: height, from: array) { image, errorMessage in
    guard let image = image, errorMessage == nil else {
        print(errorMessage!)
        return
    }

    DispatchQueue.main.async {
        self.imageView.image = image
        UIImageWriteToSavedPhotosAlbum(image, self, #selector(self.image(_:didFinishSavingWithError:contextInfo:)), nil)
    }
}

在哪里

func image(_ image: UIImage, didFinishSavingWithError error: Error?, contextInfo: Any?) {
    guard error == nil else {
        print(error!.localizedDescription)
        return
    }

    print("image saved")
}