在Swift 3中绘制CGImage的直方图

Question

vImageHistogramCalculation_ARGB8888尝试将库从Swift 2转换为Swift 3版本时,我遇到了方法问题.问题是该方法仅接受"histogram"参数

UnsafeMutablePointer<UnsafeMutablePointer<T>?> 

但是Swift 3的构造

let histogram = UnsafeMutablePointer<UnsafeMutablePointer<vImagePixelCount>>(mutating: rgba)  

返回unwrapped值,所以我无法将其强制转换为正确的类型.

编译器错误是:

:无法使用类型'(mutating:[UnsafeMutablePointer])'的参数列表调用类型'UnsafeMutablePointer？>'的初始值设定项

你有什么想法吗？我试着添加"？" 到直方图常数,但后来我收到错误:

'init'不可用:使用'withMemoryRebound(to:capacity:_)'临时查看内存作为另一种布局兼容类型.

有一些编译器建议,但我不知道如何使用它.

Answer 1

演员UnsafeMutablePointer<vImagePixelCount>?:

let alphaPtr = UnsafeMutablePointer<vImagePixelCount>(mutating: alpha) as UnsafeMutablePointer<vImagePixelCount>?

完整的编译示例:

var inBuffer = vImage_Buffer() // set your buffer here

let alpha = [UInt](repeating: 0, count: 256)
let red = [UInt](repeating: 0, count: 256)
let green = [UInt](repeating: 0, count: 256)
let blue = [UInt](repeating: 0, count: 256)

let alphaPtr = UnsafeMutablePointer<vImagePixelCount>(mutating: alpha) as UnsafeMutablePointer<vImagePixelCount>?
let redPtr = UnsafeMutablePointer<vImagePixelCount>(mutating: red) as UnsafeMutablePointer<vImagePixelCount>?
let greenPtr = UnsafeMutablePointer<vImagePixelCount>(mutating: green) as UnsafeMutablePointer<vImagePixelCount>?
let bluePtr = UnsafeMutablePointer<vImagePixelCount>(mutating: blue) as UnsafeMutablePointer<vImagePixelCount>?

let rgba = [redPtr, greenPtr, bluePtr, alphaPtr]

let histogram = UnsafeMutablePointer<UnsafeMutablePointer<vImagePixelCount>?>(mutating: rgba)
let error = vImageHistogramCalculation_ARGB8888(&inBuffer, histogram, UInt32(kvImageNoFlags))

// alpha, red, green, blue are set now