ios - 在 Swift 3 中绘制 CGImage 的直方图

Question

我在尝试将库从 Swift 2 转换为 Swift 3 版本时遇到了 vImageHistogramCalculation_ARGB8888 方法的问题。问题是该方法仅接受“直方图”参数作为

UnsafeMutablePointer<UnsafeMutablePointer<T>?> 

但 Swift 3 构造

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

返回未包装的值，因此我无法将其转换为正确的类型。

编译错误是:

: Cannot invoke initializer for type 'UnsafeMutablePointer?>' with an argument list of type '(mutating: [UnsafeMutablePointer])'

你有什么想法吗？我试着加“？”直方图常量但随后我收到错误:

'init' is unavailable: use 'withMemoryRebound(to:capacity:_)' to temporarily view memory as another layout-compatible type.

有一些编译器建议，但我不知道如何使用它。

Answer 1

转换为 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