ios - 线程 1 : EXC_BAD_ACCESS (code=EXC_I386_GPFLT)

Question

在我的 swift 项目中，我有两个类一起工作来保存图像的像素值，以便能够修改红色、绿色、蓝色和 alpha 值。安UnsafeMutableBufferPointer包含许多由 Pixel 类对象组成的咬合。

我可以与持有 UnsafeMutableBufferPointer<Pixel> 的类进行交互属性(property)。我可以访问该对象的所有属性，并且一切正常。我遇到的唯一问题是 UnsafeMutableBufferPoint<Pixel>试图用我的 Pixel 对象循环遍历它，但线程 1 一直崩溃:EXC_BAD_ACCESS (code=EXC_I386_GPFLT)异常。

init!(image: UIImage)
{
    _width = Int(image.size.width)
    _height = Int(image.size.height)

    guard let cgImage = image.cgImage else { return nil }

    _width = Int(image.size.width)
    _height = Int(image.size.height)
    let bitsPerComponent = 8

    let bytesPerPixel = 4
    let bytesPerRow = _width * bytesPerPixel
    let imageData = UnsafeMutablePointer<Pixel>.allocate(capacity: _width * _height)
    let colorSpace = CGColorSpaceCreateDeviceRGB()

    var bitmapInfo: UInt32 = CGBitmapInfo.byteOrder32Big.rawValue
    bitmapInfo |= CGImageAlphaInfo.premultipliedLast.rawValue & CGBitmapInfo.alphaInfoMask.rawValue
    guard let imageContext = CGContext(data: imageData, width: _width, height: _height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo) else { return nil }
    imageContext.draw(cgImage, in: CGRect(origin: CGPoint.zero, size: image.size))

    _pixels = UnsafeMutableBufferPointer<Pixel>(start: imageData, count: _width * _height)
}

该函数是导致程序崩溃的部分。崩溃的确切部分是循环遍历 rgba.pixels 的 for 循环。 rgba.pixels 是 UnsafeMutableBufferPointer。

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any])
{
    let image: UIImage = info[UIImagePickerControllerEditedImage] as! UIImage!

    let rgba = RGBA(image: image)!

    for pixel in rgba.pixels
    {
        print(pixel.red)
    }

    self.dismiss(animated: true, completion: nil);
}

这是我创建 UnsafeMutableBufferPointer<Pixel> 的构造函数。有没有更简单的方法来做到这一点，并且仍然能够获取 RBGA 值并轻松更改它们。

Pixel 类是 UInt32值被分成四个 UInt 8值。

我是否使用了错误的构造来保存这些值，如果是，是否有更安全或更容易使用的构造？或者我在访问像素值时做错了什么？

Answer 1

这就是我获取图像像素的方法 -

// Grab and set up variables for the original image
    let inputCGImage = inputImage.CGImage
    let inputWidth: Int = CGImageGetWidth(inputCGImage)
    let inputHeight: Int = CGImageGetHeight(inputCGImage)

    // Get the colorspace that will be used for image processing (RGB/HSV)
    let colorSpace: CGColorSpaceRef = CGColorSpaceCreateDeviceRGB()!

    // Hardcode memory variables
    let bytesPerPixel = 4 // 32 bits = 4 bytes
    let bitsPerComponent = 8 // 32 bits div. by 4 components (RGBA) = 8 bits per component
    let inputBytesPerRow = bytesPerPixel * inputWidth

    // Get a pointer pointing to an allocated array to hold all the pixel data of the image
    let inputPixels = UnsafeMutablePointer<UInt32>(calloc(inputHeight * inputWidth, sizeof(UInt32)))

    // Create a context to draw the original image in (aka put the pixel data into the above array)
    let context: CGContextRef = CGBitmapContextCreate(inputPixels, inputWidth, inputHeight, bitsPerComponent, inputBytesPerRow, colorSpace, CGImageAlphaInfo.PremultipliedLast.rawValue | CGBitmapInfo.ByteOrder32Big.rawValue)!

    CGContextDrawImage(context, CGRect(x: 0, y: 0, width: inputWidth, height: inputHeight), inputCGImage)

请记住，这不是 Swift 3 语法(如果您使用的是 Swift 3 语法)，但这是基本算法。现在要获取每个像素的单独颜色值，您必须实现这些函数 -

func Mask8(x: UInt32) -> UInt32
{
    return x & 0xFF
}

func R(x: UInt32) -> UInt32
{
    return Mask8(x)
}

func G(x: UInt32) -> UInt32
{
    return Mask8(x >> 8)
}

func B(x: UInt32) -> UInt32
{
    return Mask8(x >> 16)
}

func A(x: UInt32) -> UInt32
{
    return Mask8(x >> 24)
}

要在处理 RGBA 值后创建全新的颜色，请使用此函数 -

func RGBAMake(r: UInt32, g: UInt32, b: UInt32, a: UInt32) -> UInt32
{
    return (Mask8(r) | Mask8(g) << 8 | Mask8(b) << 16 | Mask8(a) << 24)
}

要迭代像素数组，您可以这样做 -

var currentPixel = inputPixels
for _ in 0..<height
    {
        for i in 0..<width
        {
            let color: UInt32 = currentPixel.memory
            if i < width - 1
            {
                print(NSString(format: "%3.0f", R(x: color), terminator: " "))
            }
            else
            {
                print(NSString(format: "%3.0f", R(x: color)))
            }
            currentPixel += 1
        }
    }