Swift 3中CGImage的绘制直方图 [英] Drawing histogram of CGImage in Swift 3

问题描述

尝试将库从Swift 2版本转换为Swift 3版本时， vImageHistogramCalculation_ARGB8888 方法有问题。问题在于该方法仅接受

I have a problem with vImageHistogramCalculation_ARGB8888 method while trying to convert library from Swift 2 to Swift 3 version. The problem is that the method accepts "histogram" argument only as

UnsafeMutablePointer<UnsafeMutablePointer<T>?> 

但是Swift 3构造

but Swift 3 construction

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

返回未包装的值，因此无法将其强制转换为正确的类型。

return unwrapped value, so I can't cast it to properly type.

编译器错误是：

：无法为类型$ b调用初始化程序$ b'UnsafeMutablePointer？>'和
类型为'（muting：
[UnsafeMutablePointer]）'的参数列表'

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

您有一些想法吗？我试图添加？到直方图常量，但随后收到错误：

Have you some ideas? I tried to add "?" to histogram constant but then I receive error:

'init'不可用：对$使用$ withMemoryRebound（to：capacity：_） b $ b暂时将内存视为另一种与布局兼容的类型。

'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。

there is some compiler suggestion but I have no idea how can use it.

推荐答案

是否已转换为 UnsafeMutablePointer< vImagePixelCount>？：

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

完成，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

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