Swift OpenGL未解析的标识符kCGImageAlphaPremultipliedLast [英] Swift OpenGL unresolved identifier kCGImageAlphaPremultipliedLast

问题描述

我收到'kCGImageAlphaPremultipliedLast'的未解决的标识符错误。斯威夫特找不到它。这在Swift中可用吗？

I am getting a unresolved identifier error for 'kCGImageAlphaPremultipliedLast'. Swift can't find it. Is this available in Swift?

var gc = CGBitmapContextCreate(&pixelData, width: width, height: height, bitsPerComponent: 8, bytesPerRow: width*4, imageCS, bitmapInfo: kCGImageAlphaPremultipliedLast);

推荐答案

CGBitmapContextCreate的最后一个参数（）被定义为结构

struct CGBitmapInfo : RawOptionSetType {
    init(_ rawValue: UInt32)
    init(rawValue: UInt32)

    static var AlphaInfoMask: CGBitmapInfo { get }
    static var FloatComponents: CGBitmapInfo { get }
    // ...
}

其中可能的alpha info位被单独定义为枚举：

where the possible "alpha info" bits are defined separately as an enumeration:

enum CGImageAlphaInfo : UInt32 {
    case None /* For example, RGB. */
    case PremultipliedLast /* For example, premultiplied RGBA */
    case PremultipliedFirst /* For example, premultiplied ARGB */
    // ...
}

因此，您必须将枚举转换为其基础 UInt32 价值
，然后从中创建一个 CGBitmapInfo ：

Therefore you have have to convert the enum to its underlying UInt32 value and then create a CGBitmapInfo from it:

let bitmapInfo = CGBitmapInfo(CGImageAlphaInfo.PremultipliedLast.rawValue)
let gc = CGBitmapContextCreate(..., bitmapInfo)

Swift 2更新： CGBitmapInfo 定义更改为

public struct CGBitmapInfo : OptionSetType

并且可以用

let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.PremultipliedLast.rawValue)

这篇关于Swift OpenGL未解析的标识符kCGImageAlphaPremultipliedLast的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！