image - 在 Swift 3 中使用 CGPoint 从图像中获取像素颜色

Question

我在 Swift 3 中尝试这个 PixelExtractor 类，得到一个错误；
无法使用类型为“(UnsafeMutableRawPointer?)”的参数列表调用类型“UnsafePointer”的初始化程序

class PixelExtractor: NSObject {

let image: CGImage
let context: CGContextRef?

var width: Int {
    get {
        return CGImageGetWidth(image)
    }
}

var height: Int {
    get {
        return CGImageGetHeight(image)
    }
}

init(img: CGImage) {
    image = img
    context = PixelExtractor.createBitmapContext(img)
}

class func createBitmapContext(img: CGImage) -> CGContextRef {

    // Get image width, height
    let pixelsWide = CGImageGetWidth(img)
    let pixelsHigh = CGImageGetHeight(img)

    let bitmapBytesPerRow = pixelsWide * 4
    let bitmapByteCount = bitmapBytesPerRow * Int(pixelsHigh)

    // Use the generic RGB color space.
    let colorSpace = CGColorSpaceCreateDeviceRGB()

    // Allocate memory for image data. This is the destination in memory
    // where any drawing to the bitmap context will be rendered.
    let bitmapData = malloc(bitmapByteCount)
    let bitmapInfo = CGBitmapInfo(rawValue:   CGImageAlphaInfo.PremultipliedFirst.rawValue)
    let size = CGSizeMake(CGFloat(pixelsWide), CGFloat(pixelsHigh))
    UIGraphicsBeginImageContextWithOptions(size, false, 0.0)
    // create bitmap
    let context = CGBitmapContextCreate(bitmapData, pixelsWide, pixelsHigh, 8,
    bitmapBytesPerRow, colorSpace, bitmapInfo.rawValue)

    // draw the image onto the context
    let rect = CGRect(x: 0, y: 0, width: pixelsWide, height: pixelsHigh)
    CGContextDrawImage(context, rect, img)

    return context!
}

func colorAt(x x: Int, y: Int)->UIColor {

    assert(0<=x && x<width)
    assert(0<=y && y<height)

    let uncastedData = CGBitmapContextGetData(context)
    let data = UnsafePointer<UInt8>(uncastedData)

    let offset = 4 * (y * width + x)

    let alpha: UInt8 = data[offset]
    let red: UInt8 = data[offset+1]
    let green: UInt8 = data[offset+2]
    let blue: UInt8 = data[offset+3]

    let color = UIColor(red: CGFloat(red)/255.0, green: CGFloat(green)/255.0, blue: CGFloat(blue)/255.0, alpha: CGFloat(alpha)/255.0)

    return color
}

}

修复这个错误。

let data = UnsafePointer<UInt8>(uncastedData)

->

let data = UnsafeRawPointer(uncastedData)

得到其他错误； '输入'UnsafeRawPointer？'没有下标成员的

如何修改这个错误？

Answer 1

当你有 UnsafeRawPointer 时，你可以写这样的东西在您的 data :

    let alpha = data.load(fromByteOffset: offset, as: UInt8.self)
    let red = data.load(fromByteOffset: offset+1, as: UInt8.self)
    let green = data.load(fromByteOffset: offset+2, as: UInt8.self)
    let blue = data.load(fromByteOffset: offset+3, as: UInt8.self)

否则，您可以获得 UnsafeMutablePointer<UInt8>来自您的 uncastedData (假设它是 UnsafeMutableRawPointer ):

    let data = uncastedData.assumingMemoryBound(to: UInt8.self)